Good evening everyone, thanks for coming. My name is Tom Elliman and I have the pleasure of serving as Greater Portland Landmarks President at the culmination of this, our 50th anniversary year. We gather here this evening to recognize many of you who have contributed to advancing the mission of Greater Portland Landmarks since 1964 and to give special honor to Earl Shuttleworth, who has dedicated his life's work to the history, architecture, and historic preservation of this city and the state of Maine, and with whom I have the honor of serving in the Maine Historic Preservation Commission. Before we get too far into the program, I have a few people I would like to thank. First, the Masonic trustees who donated the use of this space tonight in recognition of the help and interest landmarks has given as they work to preserve this building. Second, to Blue Elephant Catering, who has worked closely with and has tirelessly supported us in the months leading up to this event. And to special supporters this year, including 118 on Munjoy Hill, the Heritage Company Coppersmiths, and Wright Ryan Construction. Also our 50th anniversary year sponsors, including the Danforth Group and JB Brown and Sons. Plus, to Candice Lee, our event chairperson and extraordinary planner for this evening, Candice, could you stand up please? And of course, to our lead 50th anniversary sponsor, the Dead River Company. Our strong programming and educational events are also attributable to all of you in this room who have made this year very successful for greater Portland landmarks. We are very grateful to all of you. Give yourselves a hand. Now it's my pleasure to introduce Sharon Miller, our 50th anniversary chairperson for a few remarks. Sharon. Thank you, Tom. I want to add my thanks to Tom, to everyone who made the 50th anniversary a spectacular success. I look around. I see trustees, former trustees, the people who served on the 50th committee. I wish you'd all stand, the 50th committee. I see, come on guys, you did all the work. We had a terrific team and with former trustees, current members, and the staff of greater Portland landmarks, who got so much extra work dumped on their plate that they weren't expecting and carried it all out with a smile and cheers. So I applaud them as well. We started planning for the 50th more than two years ago and our first visit was to Bob Moore who's the president of Dead River because we had an incredible schedule of events. All we needed was some money. So we went in and had a wonderful visit and I was shocked that we put out an amount that we didn't know that anyone would take. He said, sure, yes. So I said it wasn't just a lead gift, it was really an inspirational gift because it gave us the courage to go and ask others and we were also very grateful to J.B. Brown and the Danforth Group for also signing on the sponsors of the 50th. But also, all of the people who came to all of these events made it a very big financial, educational visibility success and I thank you all. Now, I think I'm here just, I was supposed to be introducing Bob Moore and I was really looking forward to it, but he could not come at the last minute because of an unforeseen issue that he had to deal with. So he called me today and said, could you please read my remarks? I said, well, sure. So instead of introducing him, I know how much Bob loves that part of his job of supporting wonderful causes in the community. He loves going to events and speaking. And they're really committed to doing good in the communities where they work. So he really regrets it, but I know I can't stand in for him. I won't do him justice, but I know you'll be heartened by his words. So instead of changing his whole speech so it made any sense, I'm asking you to just pretend this is a letter from Bob to each of you. Then I don't have to change all the nouns and everything. So here's Bob's letter to you. First, I wanted to spell the notion that the only reason I was asked to speak tonight is because I've lived here long enough and I'm personally old enough to be considered a greater Portland landmark. Longevity does, however, play a role in why I am here and why Dead River Company is so supportive of greater Portland landmarks and its mission. Dead River Company was founded in 1909. There aren't many companies like Dead River left in Maine. Those that have grown for more than 100 years under the guidance and ownership of the founding family. That alone is something for all of us at Dead River Company are very proud of. We have grown and expanded, but we've done so while preserving our core values of service and responsibility to the many communities we serve. Embracing the future is essential for progress and healthy growth. But so is honoring the past.  Supporting this event and honoring those who've served it so well seemed like a natural fit.  In fact, I've lived in just about every neighborhood in Portland. The greater Portland areas where I grew up, it's my home. It's where my children grew up, it's their home. Portland's history is our history. I remember riding the first escalator in Maine at the old Sears and Roebuck store over on Free Street. I've seen the transformation that has occurred here. Many of them exciting and forward looking, others not so much. When I was in Greeley Junior High, avidly pursuing a curriculum of baseball, basketball, and playground fights, my teacher, Gladys Berkeley, took me in hand and whipped me into academic shape. She took me to the town library, showed me how to find books I would like and showed me how to check them out. She led a spark of curiosity and a love of reading. Enough so that by the time I was ready for high school, I was able to get a full scholarship to the Lawrenceville School, a prep school in New Jersey. Now, that's a longer story for another time. But I bring it up because I began taking the train regularly from Portland to Trenton, New Jersey. Back then, the train left from beautiful Union Station. We all know that with the advent of air travel and the proliferation of automobiles, people's travel preferences changed. Why ride for six hours on a train when you could take your own car, stop when you want, where you want? Americans love their cars. Train travel across the country slowed to a trickle and train stations closed. Portland was no exception. Federal money was made available for urban renewal and cities got in line to take advantage. Portland was no different. Union Station was a chiseled pink granite towering Romanesque gem that was replaced with a low-slung concrete and corrugated metal eyesore. Losing that landmark in exchange for a strip mall was not a fair trade. It was an architectural tragedy. In hindsight, it's easy to stand here aghast and say, what were they thinking? But there was no greater Portland landmarks on hand to say, there's a better way. There isn't a city in America that doesn't have a Union Station type story to tell. At least we can say that Portland's Union Station did not die in vain. The destruction of Union Station led a woman named E.S. Sills to form what eventually became greater Portland landmarks. This organization has risen from the rubble of Union Station to not only save other great landmarks from a similar fate, but also to educate and inform the greater public as to the value of historic preservation. It's been a productive 50 years. Here's to 50 more, Bob. So that's from Bob Moore. Thank you, Bob. And thank you, Dead River. And I personally would like to thank Greater Portland Landmarks for the honor of working with so many talented and committed people on a really fun project for the past two years that hopefully will pave the way for an even more successful 50 years looking ahead. Thank you. Good evening. No organization can remain as robust and influential as Greater Portland Landmarks has been for 50 years without the scores and hundreds of strong and influential individuals who have given over their time and talents. We will now honor all of you by reading a very brief summary of each of the five decades challenges and accomplishments. And mentioning each of the presidents and executive directors by name. We do want to applaud each of you, but if you could please hold that applause until the end, I'm sure it'll be much more meaningful for all of us. But when you do hear your name, it would be great if you could just wave to the crowd and we'll try to wave back. 1964 to 1973, creating an organization. The demolition of Union Station in 1961 put in motion a movement under the guidance of Mrs. Edith Sills that created Greater Portland Landmarks in 1964. In those early years, landmarks started architectural surveys, published a newsletter and walking tours, saved the Daniel Howe House and created the advisory service. With an infusion of volunteer hours and funds from the junior league, landmarks hired a part-time executive director, created the Spring Street Historic District, which is listed on the national register and saved the Gothic House by moving it to Spring Street and published the Portland book, just to mention a few things. Those presidents were Carlton Smith, Kinvin Roth, Susan Sewell, and Peter L. Murray. The executive directors were Pamela Plumb and Stephen Snell. And I have to mention a few others, including Franny Peabody, Ursula Byer, Jane Moody, and Sally Rand, who were very active. 1974 to 1983, growing the organization and its muscle. Landmarks steadily built its membership and influence in the community. It established annual awards, started walking tours and a marker program to build public awareness, compiled with the Main Historic Preservation Commission, and historic building inventory, and saved the H.H. Hay Building through the Revolving Fund. It assumed management of the Portland Observatory from the city. Landmarks worked hard, but ultimately unsuccessfully, to pass an historic district ordinance in Portland. Those presidents were Mary Louise Sprague, Pamela Plumb, James Graham, Gordon Grimes, Patricia McGraw-Randerson, and Lee Urban. The executive directors were Will Lee Roberts, Joel Russ, and Paula Craighead. 1984 to 1993, actively engaging in urban planning and design. In 1984, landmarks received a preservation honor award from the National Trust for Historic Preservation. Landmarks participated in the conversion of the Rosa True School to housing, launching a significant trend in the conversion of old school buildings in Portland. Landmarks pushed for more city controls for the protection of historic buildings and areas. It sued the city over the proposed long wharf development for failing to adhere to its own planning policies, and used the demolition of the John B. Carroll block to push for a stronger demolition delay ordinance that saved the Tracy-Couser block. Landmarks published Congress Street, a guide to building rehabilitation and new construction, and worked with the city to prepare the Historic Resources Design Manual to support Portland's historic district ordinance, which had finally passed in 1990. In 1993, it saved the historic interior of City Hall Auditorium by proposing an alternative design, which was expected. Those presidents were Joan French, Derwood Parkinson, Seth Sprague, Laura McDill, Susan Rue, Linda Murnick, and the very reverend Stephen W. Foote. The executive directors were June Lacombe, Deborah Andrews, and Martha DePriese, who's now Martha Blake, who served for 10 years. 1994 to 2003, with the historic preservation ordinance in place, Landmarks turned its attention to strengthening its implementation and played a key role in the expansion of the district boundaries in 1997. At the same time, education programs became a more important part of Landmarks' activities. The first Old House trade show was held in 1996, and Landmarks also expanded school programs, held teacher workshops, and published the first City as a Classroom Student Workbook for third graders. Landmarks took the lead in developing a new docent recruitment program with three other organizations, called Portland's History Docents, the PhDs. Landmarks worked with others in partnerships to preserve local landmarks. In 1997, to restore the Civil War Memorial in Monument Square, and the $1.3 million campaign to save the observatory and install new interpretive exhibits. Landmarks received a preservation honor award from the National Trust for historic preservation for that effort. Those presidents were Victoria Bonnebaker, Lynn Schaefer, Hillary Bassett, Daniel Squire, and Julie Ann Larry. Executive directors were Victoria Loring and Hillary Bassett. In 2004, Landmarks sold the Crockett Hunt House at 165 State Street, which had been our home since 1977. We began an intensive effort to find a new, highly visible location closer to downtown with a strong, civic presence. That dream became a reality in 2009, when we raised over $2 million to purchase and preserve the Stafford House, built in 1858, designed by Charles Alexander, as our new home. As advocates, we celebrated the creation of the Congress Street Historic District in 2010, which was unanimously approved by the city council. In 2009, we collaborated to hire a field representative to strengthen preservation services. And in 2012, we launched Places in Peril, our new endangered properties program. Our advocacy expanded to preserve these places in peril, undo urban renewal, and advocate for new historic districts. We continued our preservation publishing with Deering, a companion to the Portland Book, the energy efficient old house in our award winning new City as a Classroom workbook, which is now required text for all Portland 3rd graders. Those presidents were Jeffrey Melhuis, John Knox, Malcolm Collins, Sally Oldham, Marjorie Getz, and our current Tom Elliman, and the executive director for this entire decade has been none other than Hillary Bassett. And now, if all of those presidents' executive would please stand. Could you please stand, all of you that are here? And we would like to hear your- Hi, I'm Hillary Bassett, the current executive director of Greater Portland Landmarks, and I'd like to introduce three people who are going to pay a tribute to our special guests this evening. They are Seth Sprague, advisory trustee and former president, Pam Plum, advisory trustee, former president and former executive director, and Deb Andrews, former executive director and manager of Portland's Historic Preservation Program. And we'll start with Seth. Thank you, Hillary. And thank you for asking me to, my assignment tonight is to read a letter from none other than Christopher Monkhouse, Earl's lifelong friend, who unfortunately couldn't be here tonight. And those of you who know Christopher will know that my delivery is not going to compare with his, but I did wear a bow tie in his honor. For those who don't know, Christopher is a Portland native who grew up in one of John Calvin Steven's most beautiful homes on Bowdoin Street, and Christopher is the curator of European decorative arts at the Arts Institute of Chicago. He writes, dear Hillary, thank you for inviting me to make remarks about Earl G. Shettleworth Jr. as part of your 50th anniversary celebration of the foundation of Greater Portland Landmarks. As one of the original incorporators, along with Elizabeth Ring, John Pankost, John Calvin Stevens Second, Philip Wadsworth, Robert Albion, and Edith Sills, and the only surviving member of that august group of concerned citizens and ardent preservationists, nobody is more deserving of being honored for his founding role in your organization. I had the good fortune to be introduced to Earl by his Deering High School history teacher, the aforementioned Elizabeth Ring, in spring 1964. The same year, Landmarks was founded. As I often frequented the main historical society's reading room, went home on vacation from Deerfield Academy, Miss Ring then serving as vice president and acting director of the society came over to me one day with the suggestion that I should meet Earl Shettleworth, as she felt we had many interests in common. So it was a range for us to meet in the reading room the very next day. And as they say, the rest is history. For starters, Earl introduced me to the Daniel Howe House and then various sites on the eastern promenade that were terra incognita for somebody who had grown up on the other promenade. And even under my very nose in the western cemetery, Earl showed me the fragmented remains of the headstone for the Portland portraitist Charles Octavius Cole, whose profession was carved into the marble. Somewhat grandly as artiste. What pleasure that final E gave to Earl. As we realized that the headstone was not long for this world, we seriously contemplated taking preservation into our own hands and removing it on the spot. While our law-abiding ways got the better of us, that would not be the only time we contemplated a larseness act especially in the case of vulnerable architectural fragments. However, we invariably made do with a snapshot using my father's polaroid camera. As our friendship stretches over 50 years, I could easily regale you all evening with stories pertaining to our collecting and preserving Maine's cultural past in tandem. However, one in particular stands out. Once I had become a curator of decorative arts at the Museum of Art, Rhode Island School of Design and Providence, and acquired the requisite station wagon for the performance of my job, Earl knew that he could rely on me when time was of the essence to keep important documents out of harm's way. He had only just learned that the former offices of the Maine and New Hampshire Granite Company in J-Maine were going to be destroyed, along with the firm's archive containing literally thousands of Incan linen architectural drawings. So Earl enlisted me and my station wagon for an 11th hour rescue mission on a high foliage weekend in Maine. Needless to say, leaf peeping did not figure into our agenda. Instead, we came away with virtually all of the architectural records that then were deposited in the shed attached to Earl's gardener home. Eventually, the future disposition of the drawings needed to be addressed, with Earl and me agreeing that the drawings should be redistributed geographically, with drawings earmarked for depositories closest to their actual building sites. That way, all Maine projects ended up in Augusta in the architectural archive maintained by the Maine Historic Preservation Commission, while the rest of the projects pertaining to New England went to the Society for the Preservation of New England Antiquities, now Historic New England based in Boston. And as Earl recently reminded me, rolls of blue lines for 12 buildings by Daniel Burnham were donated to the Ryerson and Burnham Library at the Art Institute of Chicago. I was rewarded for my labors and loan of my station wagon with the remainders of the drawings going to the Heinz Architectural Center at the Carnegie Museum of Art in Pittsburgh, where I was the founding curator from 1991 to 1995. That way, the drawings for the nearby buildings of the Carnegie Institute of Technology, now Carnegie Mellon University, literally came home, as their granite foundations originated in the quarry of the Maine and New Hampshire granite company in J. In conclusion, I think it's fair to say that Earl and I have both spent our professional careers, not only as historians, preservationists and curators, but also befitting two boys who grew up in Portland as harbor masters. It has been our mutual goal to get ships into safe ports, and not necessarily our own. Architectural records are most meaningful if they are in the hands of those who appreciate what they have and close to the sites of the buildings they record. The final disposition of the archive of the Maine and New Hampshire granite company is a case in point. Through frequently lecturing on architectural history and preservation, Earl has developed a robust presentation style that can be heard over the din of foghorns, again invoking the analogy to a harbor master. Earl's first public lecture, appropriately enough, was arranged by Miss Ring on Portland architecture for a meeting of the College Club in January 1964. As was often the case, College Club gatherings frequently took place in the living room of Edith Sills on Vaughan Street, where I might add many of the early meetings of greater Portland landmarks also occurred. So if this were London, the Greater London Council would be affixing a circular wedgewood blue ceramic plaque to 134 Vaughan Street, noting its seminal role in the formation of greater Portland landmarks and the site of Earl G. Shettleworth Jr.'s first public lecture on Portland architecture. Fifty years later, Earl is still informing and inspiring audiences about our built environment, with tonight being no exception. Let's end Christopher's remarks. And as I was reading Christopher's remarks and thinking about them, it made me think about how important it is for an organization to find passionate, dedicated people. Everyone here came to be involved in different ways, and we all have different stories to tell. The Messers' Monk House in Shettleworth had the encouragement of the icons Elizabeth Ring and Edith Sills. In my case, my parents imbued in me a love of history, and they introduced their children to historic preservation through the direct method. They handed out paint scrapers and blow torches. But even though my mother, Mary Louise Sprague, devoted countless hours over many years to landmarks, it was ultimately a summons from Franny Peabody that nudged me into my involvement, one that has stretched 30 years plus and has been very rewarding for me, and I'm grateful for that nudge from that most remarkable lady. Among other things, I would hope that this celebration will inspire people young and old to engage with landmarks. Fifty years of dedicated work by landmarks has helped make Portland the wonderful city that we live in today. Imagine what the next 50 years might hold. Thank you. Good evening. My name is Pam Plumb, and I am so happy to be here, and I've been so happy to see so many friends from those very, very early years, along with the ones from all the later years as well. My life was changed forever by Kinvan Roth. Kinvan Roth was showing my husband Peter and myself his house, thinking that we might rent it for one year, for Peter's one year clerkship. And he turned to me and said, what are you going to be doing, my dear? He said, beats me. I'm looking for a job. He said, well, why don't you come apply to be the Executive Director of Greater Portland Landmarks? I was 26 years old. I had just finished graduate school, or at least through a master's, and I was history of art major. That seemed impressive to him, but I told him I was a medievalist. I didn't know anything this side of the Council of Trent, but I was a quick learner. And in an astonishing leap of faith, Kinvan Roth and Sally Sewell, now Susan Thomas and a couple of other folks actually hired me to do that job. I had no idea what to do. Let me describe to you the office of Greater Portland Landmarks. In that moment, it was in the Howe House. It had been painted by the individuals who were willing to repaint the interior of the Howe House. We had an enamel kitchen table.  And we, a membership, was on index cards in a shoebox. So that's where we began. It was a time of great energy, great direct involvement. We were chasing bulldozers and trying to save buildings and trying to promote the value. The volunteer organization before I came along had already done a number of things that were pointed out by Jim Cram and gotten the organization on its way, but we were still in guerrilla warfare mode. The interesting thing to me to watch over all this time is how landmarks grew into having its place at the table, which is what it needed desperately in those early years and didn't have and it grew to have later on. There were monumental moments, the moving of the Gothic house, which started white hair in my head at the age of 27 and things like that, which were dramatic and successful for the organization. But the last thing I want to say about those early and dramatic times and it continues to present day is that whenever we had a question, we would say, where's Earl? Earl will know. What about that building over there? Earl will know. Well, why was that street developed that way? Well, Earl will know. And you know what? That's what we're still saying. Earl will know. In preparing my remarks tonight, I realized that I've known Earl for 30 years this fall. I came to serve as Executive Director of Greater Portland Landmarks, very green, and he was very helpful to me and continues to be an inspiration. I consider an Earl a rock star and so I am very honored to recognize him tonight. Critical to any successful historic preservation effort is an understanding of the place you're trying to preserve. It's pretty difficult to make the case for saving something that people just don't understand. Out of understanding rose appreciation and ultimately the motivation and conviction to save and protect special places. How lucky we are then in a state so rich in historic resources to have Earl Shettleworth. Since his early teens, Earl has been helping the citizens of Maine in communities large and small to understand what they have, what the historic buildings in their community tell them about their community's past and how relevant they are to today. For 50 years, Earl has researched and documented the historic architecture and cultural history of Maine. He's crisscrossed the state, sharing this information in countless talks and presentations. He's authored at least 28 publications, I checked with your staff to see if that's correct, I'm not quite sure, but he's authored at least 28 publications about various aspects of Maine's architectural history and co-authored or contributed to at least as many. Whenever there's a project that involves a significant historic property, the press calls Earl, knowing that he will not only be able to give detailed information about the particular property, but also help the readers understand its role in a larger context. All of this he's done while running a very busy and effective state historic preservation office. As you may or may not know, Earl is the longest serving state historic preservation officer in the country. As director of the Maine Historic Preservation Commission, he has attracted and assembled a very knowledgeable, capable, and committed staff. Indeed, it's the very constancy of Earl's leadership and the continuity within his staff that sets the Maine Historic Preservation Commission apart from its counterparts in other states. In my role with the city of Portland, Earl and his staff at the commission have been inordinately and repeatedly helpful, always helpful. Not only providing information and resources and wise counsel on numerous initiatives, but also providing funding to undertake projects that the city wouldn't have had the resources to do otherwise. A couple of recent examples include an architectural survey of the India Street neighborhood and an historic assessment of the Portland Company. Earl, for the truly extraordinary contribution you have made to the cause of historic preservation in Maine and for your continued passion for the cause, I thank you. Thank you. This is the good thing about trusting all the great people that work with you. They will come through. This has been an extraordinary year for greater Portland landmarks as we've celebrated our 50th anniversary and our guest of honor, Earl Shuttleworth, has been involved throughout. We opened the year with a photography exhibition co-curated by Earl that showed how Portland has evolved through current and vintage images. In March, Earl introduced our keynote speaker, distinguished Metropolitan Museum of Art Curator, Morrison Heckscher, who shared insights about the preservation movement. And Earl played an essential role in developing an installation we are about to mount, telling the story of Portland's preservation movement at our Safford House headquarters. Our guest of honor tonight, Earl Shuttleworth, not only helped start landmarks, but he continues to be with us every step of the way. Earl is a prime example of what we have heard again and again this year. It's the people who make preservation happen, whether it be research, saving buildings, gathering historic images, providing deep background information, sharing advice on a wide array of topics about architecture and history, not to mention public speaking. Earl is there, or I should say everywhere. Earl never says no. He says, how can I help? Earl remembers even buildings that have long since gone. Earl is the institutional memory. Earl has spent his whole career starting at age 14, dedicated to learning about and preserving the authentic historic buildings and landscape that define Greater Portland and Maine. As Greater Portland Landmarks celebrates our 50th anniversary, it's my great pleasure to honor Earl G. Shuttleworth for his founding of Greater Portland Landmarks more than 50 years ago and for his service throughout his life to historic preservation in Maine. So we have a special thing for you before your remarks, and I'm inviting Chris Kloss to our Preservation Services Advisor to join me in revealing. So I wanted to mention this is a photograph of the interior of the Custom House that is by Heath Paley, who is here tonight somewhere, and done recently after the new restoration of the Custom House, which Earl's office and landmarks have been involved in. So we'd like to offer this as a token of our appreciation for your excellent service to all of us in the state of Maine. And now I'd like to invite Earl to make a few remarks. Well, first, I just want to thank everyone for coming. I want to thank the kindness that has been shown to me by Greater Portland Landmarks this evening. This is a very, very special event in my life. Illusion has been made already to the fact that I may be the only surviving member of the group who signed the original incorporation, and I believe that's correct. And I want to just mention very briefly before I get into my prepared remarks that Eva Sills had a wonderful wit about her. And I can remember very vividly at 16 after we went into Peter and Cairo's seniors' law office in this building, which I'll allude to again in a few moments. The papers were signed, and then she turned to me and she said, you know, someday you'll be the only one left to tell about this. And she was right. Now, she's also the Edith Sills who, as Christopher Monkhouse reminded us, hosted my first talk 50 years ago. And at the tea afterwards, Edith, who of course had spent 30 years as the first lady of Bowdoin, a very gracious and yet a very witty and sharp lady, she came up to me and she said, now Mr. Shuttleworth, of course she addressed all the boys at Bowdoin as Mr. And so I was also as a high school student. And she said, now Mr. Shuttleworth, she said, you know, the darkness of your slides was illuminated by the brilliance of your remarks. Had a wonderful cutting edge to it. Now in those early meetings between 1962 and 1964, I believe we may have one person in addition to myself who was in those meetings. Is Mason Smith here tonight? Did Mason make it? I don't see him. I know he was invited. But Mason Philip Smith, who's a very fine photographer now retired, he was very gracious in those days in taking photographs for the various early publications of landmarks, such as the 1965 walking tour.  So I've titled my remarks to save a city. And I'm going to use this illustrations, old postcard views, because I, among other things, I have this passion for old postcards. For most of its history, Portland believed that it was destined to be a great American city. Its motto, resurgum, and its emblem, the phoenix, symbolized its rebirth after each of four major destructions. Its ambitious spirit was noted by the English writer Anthony Trollop, who observed in his 1862 book, North America, few cities have fairer natural advantages than Portland. And I am bound to say that the people of Portland have done much in turning them to account. I doubt whether I will ever see a town with more evident signs of prosperity. And this is the view of Portland in 1865 just before the Great Fire. These evident signs of prosperity sustained Portland during the boom years of World War II shipbuilding. However, the post-World War II Portland, into which I was born in 1948, had begun to perceive itself as a city in decline. Like many of its counterparts across the nation, it viewed its 19th century form and fabric as outdated, impediments to its future, a future increasingly threatened by the automobile which ushered in these residential suburbs on Brighton Avenue and shopping malls. Portland's initial response to these changing economic and social patterns was to replace the old with the new. Thus, the 1960s became a decade of demolition, beginning with Union Station in 1961, followed by the John Muzzy House, the Falmouth Hotel, the Old Post Office, the Second Parish Church, St. Stephen's Church, and the Grand Trunk Station shown here at the foot of India Street. Dramatic as these individual losses were, a greater change resulted from renewal projects such as Bayside, Monjoy South, and the Golden Triangle. The first two projects erased 19th century working class neighborhoods, while the third destroyed blocks of commercial buildings that had provided a link between the Old Port and Monument Square. Of even greater concern was the Gruen Plan, a Robert Moses-style inner-city ring road that resulted in the Franklin Arterial and the Spring Street Arterial. The promised benefit was easier automotive access to downtown businesses, but the price was high. The first Arterial truncated Lincoln Park and separated Monjoy Hill from the rest of the peninsula. While the second Arterial, combined with the Holiday Inn that we see here, created a sterile wasteland in place of a historic streetscape. Only recently, after living for more than 40 years with the scars of these Arterials, have we begun as a city to address their social and visual impacts on our inner city. This was the challenging political landscape into which Greater Portland Landmarks came into being 50 years ago on July 10th, 1964. In the Law Office of Peter N. Cairo Sr. located here in the Masonic building where we gather tonight. In addition to your speaker who founded Landmarks that summer afternoon were architects John Calvin Stevens II and Philip Wadsworth, Maritime Historian Robert G. Albion, Maine Historian Elizabeth Ring, Portland Museum Director Johnny Pankost and Community Leader Edith Sills. The need for such an organization had first been advanced by Mrs. Sills in 1962 in the wake of Union Station's loss. Responding to the concern of many of her fellow citizens over the loss of such a prominent landmark, Edith Sills invited prominent local leaders and historians to her home at 134 Vaughan Street, which you are already getting very familiar with, to discuss strategies for historic preservation. From February 1962 to June 1964, she held monthly meetings of the Sills Committee, which led to the formation of Greater Portland Landmarks. Having been Bowdoin College's first lady for more than three decades, Mrs. Sills possessed the stature and experience to bring people together and win them to her cause. No Bowdoin boy said no to Mrs. Sills. From the beginning, the Sills Committee recognized that knowledge of Portland's history and architecture were essential to identifying and preserving the city's built environment. To Elizabeth Ring, chair of the History Department at Deering High School, which we see here, I was fortunate to attend many of the Sills Committee meetings and to participate in the first architectural surveys in 1963 and 1964, aided by my compatriots, Peter Kairos Jr. and Christopher Monkhouse. These surveys formed the basis for a slide lecture that I've already alluded to that I delivered more than 100 times between 1964 and 1966. No wonder my algebra and French grades were a little tacky. The survey also informed my writing of 52 articles on local historic buildings for the Portland Evening Express between 1965 and 1967. No sooner had Greater Portland Landmarks been incorporated than it faced its first challenge. The General Services Administration announced that the old post office at Middle and Exchange Streets would be torn down for a federal employees parking lot, now post office park. Landmarks succeeded in securing a six month stay of execution for the building, but with the revival of the old port still in its infancy, a lack of investors and uses doomed the magnificent marble structure to demolition in 1965. Today I believe developers would be lined up around the block for an opportunity to rehab this building. Another early challenge for Landmarks was the Chilton Block, shown here in the very middle of, actually it's just one in from the left, to the left is the Falmouth Hotel, then there are the Chilton Buildings, the Lower Hay Building and the Muzzy Block at the right. This is Middle Street around 1900. Another early challenge was the Chilton Block, a row of post Victorian, fire Victorian commercial buildings at Middle and Spring Streets. Acquired by the city with federal urban renewal funds, the block's removal was part of a plan to redevelop the Golden Triangle, bordered by Middle, Temple, Federal Streets. Landmarks advanced a sound proposal for the reuse of the Chilton Block, which was rejected by the city council. Successes in these years, as you've already heard, included the restoration of the Daniel Howe House on Danforth Street and the moving of the Gothic House from the Holiday Inn site to its present West End of Spring Street. Seeking to establish confidence and credibility in the community, Landmarks adopted oftentimes a very reasonable approach to historic preservation issues in the 1960s and 70s, reaching out to the city. But the organization continued to be viewed with a wary eye by city fathers and business leaders. Such was this attitude that I very specifically remember being called into City Hall in 1972 after my lecture series on the city's architecture had been covered in the press. The message was delivered to me by a senior city official that my advocacy for preservation was detrimental to Portland's economic development and that I should direct my energies elsewhere. As you can see tonight, I didn't really take this advice seriously. Gradually, however, opinion began to shift in favor of historic preservation. One factor was the dramatic resurgence of the old port. Its success initially due to a few visionary private investors such as Elvin Gilman, Henry Willett, and Frank Akers. The old port demonstrated a viable alternative to the conventional teardown policies of the time. Another factor was the implementation of the new Federal Historic Preservation Programs by the Main Historic Preservation Commission in Augusta. Just 50 years ago, this was Edmund Muskie's campaign poster for reelection to the Senate. He'd been elected in 1958 and was seeking reelection. 50 years ago, Senator Edmund Muskie identified what would become the National Historic Preservation Act of 1966. And if I were present at the creation of landmarks, I feel a little bit like I was at the preservation present at the creation of the national landmark legislation as well. Because I vividly remember in the spring of 1965, visiting Muskie's office in Washington during a summer vacation, and prophetically, Chip Stockford, who was one of his aides, handed me a draft of the National Historic Preservation Act and said, here, this is something that the senator is working on. You might be interested in reading this and letting us know what you think. Well, I've spent most of my life administering that act in Maine. This far-reaching legislation created a Federal Historic Preservation Program administered by the National Park Service in partnership with states, local governments such as the city of Portland, and nonprofit organizations such as Greater Portland Landmarks. Since 1971, the Maine Historic Preservation Commission has carried out the Preservation Act in Maine, and Portland has been a major beneficiary of the National Register of Historic Places, architectural surveys, restoration grants, certified local governments, federal and state rehab tax credits. Since 1972, the commission has nominated 73 Portland buildings to the National Register, starting with the Woodman Building, Victorian commercial block at Middle and Pearl Streets. The city's most recent additions to the register were the Nathan Clifford School in December 2013. In addition to individual listings, Portland has 12 National Register historic districts. These include the Old Port, the Spring Street area, the Deering Street area, Western Prom, and Stroudwater. The role of landscape architecture has been of particular interest to both the city and the state, and we show you Lincoln Park as an example of parts of the park system that are listed on the National Register. This initial work ultimately led to the formation of the Local Historic Preservation Board, initially created by the ordinance in 1990, strengthened a few years later, and many of the properties that were listed in the National Register either individually or as districts then became covered by the local ordinance as well. Underlying all preservation efforts is the identification of historic resources based on documentary research and an understanding of building types and styles. Expanding on the early architectural surveys by landmarks in the 1960s, the Commission, the City, and landmarks jointly published the Portland Historic Resources Inventory in 1976, a compilation of six districts and many individual structures. Since the publication of that inventory, the Commission, the City, and landmarks have sponsored more than a dozen architectural surveys, and I just show you one, Coil Park in the Deering Area off Forest Avenue, an early 20th century upper-middle-class housing development. And here would be another of the surveys, the late 19th, early 20th century summer cottages on Great Diamond Island. In 1976, the Congress created an Historic Preservation Tax Credit for the rehab of income-producing properties listed in the National Register. A parallel state credit was adopted in 1999 and strengthened in 2008. Historic Preservation Tax Credits strive to place rehabilitation on an equal footing with new construction. The purpose of these credits is to encourage adaptive reuse of historic commercial and industrial buildings in an effort to revitalize cities and towns as well as to save important parts of our heritage. And it is truly a federal, state, and local effort that works. And in the case of Portland, a hundred rehabilitation tax credit projects totaling $138 million. The most recent of which is the Eastland Hotel. Reviewing the accomplishments of the last 50 years, it is tempting for us to rest on our laurels. But as one who follows the Portland scene daily, I know that issues such as the Portland Company and House Island, Fort Scamble, shown here, are constantly emerging to require our attention. The city's current economic vitality, to which preservation has been such a major contributor, brings with it the challenge of having sound growth without sacrificing initial character. Fundamental to the future of historic preservation in Portland is continuing expansion of our understanding of the city's history and architecture through research and architectural surveys as well as through public education, lectures, walking tours, publications. Knowledge has always been our greatest strength. For example, there is still much that we have to learn about Monjoy Hill, and we see here North Street looking from Congress Street. As Abbott Lowell Cummings, my great mentor in graduate school and the former director of the historic New England, wrote in 1965, the struggle we face has long since become more than a matter of concern over an individual building of merit. Areas must now place an essential role in preserving the basic character of our older New England cities. This is what was the largest screen manufacturing factory in the world, stood on Spring Street, the Burroughs factory, swept away by the Spring Street arterial, thank you, and it's pertinent to my next point. Since the first energy crisis in the 1970s, traditional methods and materials for preserving historic buildings have been under siege. We live in an age of rapidly changing building technologies which include vinyl windows, synthetic siding, and alternative energy systems. We must continually assess the advantages and disadvantages that these technologies have for historic buildings and educate property owners accordingly. Both the landmarks advisory service and the landmark staff do an admirable job of this work. And closely linked with the methods and materials, are the professionals who care for our historic buildings. The architects, the engineers, the contractors, the conservators, and the craftspeople whose knowledge and experience are essential to that work. Fortunately, the Greater Portland area and Maine as a whole have no shortage of these technical, talented technical firms and individuals. We must support the current generation of these professionals and encourage them to train the next generation. Relying on our abundant local talent is the best way to ensure against misguided renovation projects. And I look across this room this evening and there are so many of you who have, even of your time and talent, both in your own careers and to landmarks in relation to these technical issues, and I applaud you. We also must not forget our traditional historic sites. We must actively support the institutions in Portland that have voted to preserving major landmarks that so define our city's identity. The Colonial Dames for the Tate House. The Maine Historical Society for the Wadsworth Longfellow House. The Portland Museum of Art for the McClellan House and the Clap House. Greater Portland Landmarks and the City for the Portland Observatory. The Committee to Restore the Abyssinian for the Abyssinian Meeting House. The Women's Christian Temperance Union for the Neal Dow House. The Portland Veteran Firemen's Association for the Portland Fire Museum. The Victoria Society for the Victoria Mansion. And the Maine Jewish Museum for the Et Shame Synagogue. This, by the way, actually is a postcard interior of the bacteria of the synagogue in the Jewish home for the aged in the 1920s. These early photographs of the presence of Jewish life in Portland are very rare. To add to this, I would include our religious structures, our parks, our cemeteries, many of which have support groups. And we must not forget the Portland Room of the Portland Public Library and USM's Osher Map Library and Smith's Center for Cartographic Education. Collectively, these organizations are the guardians of Portland's heritage. In this regard, we must also find ways to replace the valuable educational opportunities for Maine students that will be lost with the recent elimination of the USM American and New England Studies Program. Finally, looking into the more distant future, will our distinctive peninsula geography place us in peril to the rising ocean waters? Will Casco Bay be to Portland as the Arno is to Florence and the Adriatic to the Venice? The Portland Society of Architecture has recently begun this thought-provoking conversation, and we as preservationists need to join it. I think this view of the fishing fleet at the turn of the century after a storm is actually everybody fleeing Atlantis. But not for a while. When Landmarks was incorporated 50 years ago this summer, no one could have foreseen the vital role that historic preservation was destined to play in shaping the renaissance of the city we know today. The success of this contribution is due in large part to the commitment of the state, the city, Landmarks, the private sector, and local residents who work cooperatively and creatively for the common goal of a better Portland. Once again, we see, quote, those evident signs of prosperity that Anthony Trollop spoke of more than 150 years ago. Thank you. Earl, thank you so much for coming. It's not just a pleasure to know you, but it's an honor to have you here, and we are pleased to honor you tonight, and we are so pleased with the contribution you make to this organization, this city, and this state. And there's more. Oh, no. There's more. I was going to ask, let's see, Peter Plum and Kathleen Grammar to come up and lead us in a tribute to Earl. All right.  All right. Everybody stand up and stretch, at least those who can do. Stand up and stretch. All right. And this is your chance now, loudly with great clarity, perfect diction and pitch to honor Earl. All right. And when we get to the refrain the second time around, we're going to do it twice, and that really requires some gusto. So, are you all ready for this? Federal dwellings with flabbered façades, bungalow follies and early kick-a-huts, classical buildings with two matching wings. These are a few of all's reddered things, floor plans and door plans and ionic order, hip booths and mansards and gambles with dormers, shingle-style houses with porches galore. These are some things that Earl poorly adores. Mansions with string courses on that lash elevation, Italian villas with fine fenestrations, saving these houses what he does best. For this HBO there's never the rest. Earl's our expert, name's official preservationist. From landmarks beginning and through fifty years, we've been eating old-finch and Paris and savage and facet, north-east to Cushing and printy-wisc asset. All the great structures in our state of Maine, Earl's got on file in his lopsided grain. John Calvin Stevens and John Bundy Brown, Carbon and Trisket and Harry Bird Brown. These are the people he knows through and through, and in lectures about them, north to Peru. Maine's official preservationist. From landmarks beginning and through fifty years, we thank him, he is the... I wanted to make a couple of closing comments while you're enjoying your cake. The first landmarks is looking ahead to the coming year and the next fifty years. In fact, at eight o'clock tomorrow morning, we'll be having a meeting at Safford House to start planning for the hundredth year anniversary party. A short fifty years away, we've got to get started on these things early. After tonight's celebration, it looks like it could be pretty important. It's been quite an evening here. Because we're all together, I thought I would mention a special thanks to three recent bequests made by Edwin Currier, Nan Sawyer and Norm Nelson. During the summer of our fiftieth anniversary year, that's this past summer, landmarks trustees have set up a board designated endowment for the first time, which we hope will grow and help sustain us over the next several decades. As we close out this year, we are forming a legacy society of landmark supporters. People like you who will remember landmarks in your estate plan. We understand that some of you will pass on a percentage of your assets to landmarks, and we thank you. Please identify yourself to us. If you are one of these people, and if you are not, please consider the opportunity of leaving a legacy to landmarks in the long term. In the short term, we are planning two major events for the spring of 2015 that you all will be interested in. First, our next old house trade show, the weekend of March 28th and 29th. We'll remind you in case you forget that date. March 28th and 29th in Portland, connecting experts in the field of historic building repair and renovation with historic property owners throughout the region. And also, and this is big, an exhibition of John Calvin Stevens' paintings in partnership with the art gallery at UNE's Westbrook campus and with Earl Shettleworth serving as curator. How could we get along without him? This collection of Stevens' artwork will be displayed together for the first time, thanks to the generosity of the Stevens family, including Paul, Dodo, Nate, Jane, and others in their family. So we will again remind you about that because that's going to be tremendously important and significant to us and the whole community. And finally, I want to thank the landmark staff without whom we could not get along. And they are all, those who are here, I think are Hillary, Chris, Jen, Kate, and Maggie. I think that's it. Could you all stand up and we would give you a... I think you all know them. They do it all. And if you don't know them, you will soon, I'm sure. And to thank all who have made the 50th anniversary year such a wonderful celebration of historic preservation in this region, we look forward to doing it more and more and better and better. Thank you all for coming and good night.


to the 16th lecture in the course design and engineering of computer systems. So, in this week we are going to study a little bit more about the IO sub system in operating systems. So, let us get started. So, this is a recap of what we have seen in the course so far. So, we have studied the basics of what are computer systems, what are some of the common principles of designing computer systems. If you remember from the first week, we had studied principles like abstraction, virtualization, fixed size allocation, caching and you would have seen these principles being used over and over again in the past few weeks. We have started this course with an overview of the hardware, CPU, memory and IO devices and then we moved on to the system software layer, which is we have seen how the OS runs processes and the similar concept of virtualizing the CPU for a process was used to run virtual machines and then we have studied a little bit about how memory is accessed and managed in an operating system and this week we are going to complete our discussion of operating systems by understanding how the OS manages IO devices. In particular, we are going to focus on two types of IO devices mainly that is the hard disk or secondary storage which stores your files and the network card or the network interface which lets you communicate with other machines. So, these are the two main important subsystems in an operating system when pertaining to dealing with IO devices. So, the part that deals with files is called the file system and the part of the OS that manages the network is called the network stack and in this week we are going to study these two in a little bit more detail. So, let us get started. So, this is a brief recap of what are IO devices and how they work that we have seen in the first week of the course. So, an IO device is any device that is other than the CPU and your main memory that is there on your computer like a hard disk that stores data in blocks or other devices like network cards, keyboard which basically generate a stream of bytes or even your monitor which is an output device and so on. All of these are IO devices and you all are familiar with these. So, every IO device is usually managed by a device controller which is like a specialized microcontroller that focuses on managing the IO device. So, there is the IO device and there is the device controller which exposes or which has a bunch of registers and the CPU or the device driver in the operating system will access these registers, read and write these registers of the device controller in order to get some IO done using the IO device. So, we have seen that some common registers are the command register which is used to give a command, the device driver will write a command into the command register, the status register indicates what is the status of the IO device, the data register is used to read and write data from the IO device and so on. And device drivers communicate with the device through these registers. So, we have seen a simple example of how you read the data from a disk. So, the device driver that is running inside the operating system will give a command to the disk asking it to read say some block of data on the disk and once the command is given of course the operating system will you know whichever process gave the command it will block, it will be context switched out and the OS will run some other process simply because the disk takes a really long time in order to finish this operation as compared to the operating systems or the CPU speed. So, therefore, while the disk is executing this command the OS will go run some other process and at this point of time the disk is executing the command and when the data is ready to read whatever data has been asked to read when that is ready the device will transfer it into RAM it will perform a DMA a direct memory access and transfer the data into main memory and then it will raise an interrupt the trap instruction will run then the OS the device driver will come handle the interrupt look at the data process it further you know give it to the process unblock it all of that will be done. So, we have seen all of this before and the main reason why we use DMA is that it reduces the overhead instead of the device driver copying data from the you know some register of the device controller the device is directly putting the data in RAM which makes life easy for the interrupt handling part and this is especially important for high speed devices like disks and network cards and so on. So, in the next few lectures whatever we study they are all based on DMA. So, this is a recap of what we have seen before in the first week of the course with respect to IO devices. Now, let us begin our discussion of file systems. So, we have seen the notion of a file before a file is nothing but stream of bytes that are persistently stored on a secondary storage device like a hard disk you all know what a file is you read and write files access files all the time on your computers and traditional hard disks split a file into some fixed size blocks and store it on disk it is not stored continuously but into it is split into fixed size blocks and stored and the operating system what does the operating system have to do with files the OS does many things. First is of course the user program is given a bunch of system calls the OS X exposes an API of system calls to user programs and then the OS actually implements these system calls you know your system calls to open a file read a file write a file all of those are implemented by the operating system and the part of the operating system that is called the file system. And as you implement these system calls you will have to access the underlying disk the device you have to access and this access is done via the device driver. So, this accessing the actual device is done via the device driver and also in addition to all of these pieces we have also seen that the OS maintains a cache a disk buffer cache of the recently accessed disk blocks whatever you have read from disk via the device driver you will cache them for some more time. So, all of these things the system call implementations the device driver the disk buffer cache all of these together are used by the OS to provide the user the abstraction of files and all of this code together is called the file system. And every file system has a specific way of organizing data on disk you know how to split the file into different blocks and so on there are different ways of doing it that is not just one way of doing it which is why there are many different file systems in use in modern operating systems. So, in this lecture we are not going to go into details about any particular file system but we are going to study the general principles that hold across any file system. So, in this lecture we will begin with understanding what are the data structures that are used in a simple file system and in the next lecture we are going to study the implementation of the system calls how do you actually do open read write using these data structures. So, let us begin the first and the most important data structure in the file system in modern file systems is what is called the inode or the index node. So, what is the inode a file a variable sized file is stored in is split into fixed size blocks and stored on the disk that is if you have a large file like this you will split it into blocks and then on your disk you will have one block here one block here one block here we will not store the file contiguously but split it into fixed size blocks and this is a principle we have seen before with respect to pages in main memory and so on and why do we do this because we want to avoid fragmentation external fragmentation you do not want variable size things being stored on disk and there being gaps left between two variable size chunks we do not want to deal with that headache. So, we split the disk into fixed size blocks and we allocate storage to a file in terms of these fixed size blocks. So, once a file is split into fixed size blocks and stored noncontiguously not in you know one place but all over the disk you will need somewhere to keep track of where all a file is located on disk just like how the memory image of a process is split in across many pages in memory and you need a page table to keep track of it. Similarly, for a file also every file there is a index node or an i node which actually remembers the location of all the blocks where a file is stored the first few bytes of a file is stored in this block number the next few bytes in this block number the next few bytes in this block number. So, all of these block numbers where a file data is stored all of those are kept track of all of those block numbers are stored in the i node or the index node of a file. So, this index node of a file also where is this index node stored this i node is also stored on disk just like how your file data is split into blocks and stored on disk similarly the i node is also stored on disk somewhere and this i node has the block numbers of all the blocks of a file and this i node need not fit in one disk block again it can be split into multiple disk blocks you will have a hierarchical structure that we will see in a little bit. So, conceptually it is similar to a page table of where you do fixed size allocation non-contiguous allocation and keep track of all that information in an index block. So, the i node stores all metadata about a file not just the location of these data blocks the disk block numbers of the file is one type of metadata about a file. So, understand the difference between the data of a file which is the actual contents of the file and the metadata of a file which is information about the file which includes disk block numbers various other things like what is the file size permissions who can read who can write when was the last time the file was accessed modified all of this constitutes the metadata of a file and the i node stores all of that information also and this i node is also stored on the disk along with the data blocks of a file. So, let us understand the structure of the i node in a little bit more detail. So, every i node in a file system has a unique number the i node number it is like say the role number of a student which uniquely identifies the i node on disk and therefore, from the i node you can uniquely identify a file. So, given a file if you know its i node number you can locate the i node on disk and once you locate the i node you know where all the data blocks are there of the file and you can get all the information about the file by knowing the i node number of the file. So, this is a very important piece of information about the file. Now, inside the i node how do you store all the block numbers of a file a file can have many blocks typical block sizes on a traditional hard disk is say 512 bytes. So, if your file is larger than that you will the file will be stored in multiple data blocks and how do you store all of these data blocks in an i node we are going to understand now. So, note that all of the data blocks of a file may not even fit in one i node you might have to use multiple different blocks they may not fit in one i node disk block. So, the way it is done is again the same idea of hierarchically storing like we have seen in page tables a similar idea is used. So, the typical i node looks like this the first few block numbers of a file the first few blocks of a file their numbers are directly stored in the i node that is the i node will have pointers direct pointers to the first few blocks of a file.  So, this way the i node will have a first few direct blocks and then of course you cannot store large number of things at some point space in the i node will run out. Then once all the direct blocks are full once your file size exceeds these direct blocks then what you will do is you will create an indirect block which in turn has the block numbers of the file and this indirect block number that will be stored in the i node. So, there will be a single indirect block which has the numbers of the data blocks of the file and the number of the single indirect block is stored in the i node. So, without occupying much space you are able to store many more block numbers using a single indirect block. Then what if this is also full what of your file is bigger than this? Then you will have a double indirect block which is your i node will have a block number of a double indirect block and this double indirect block will have the block numbers of several single indirect blocks and these single indirect blocks will have the actual block numbers of the file that is you have a two level hierarchy. The block numbers of the file are stored in these single indirect blocks these block numbers are stored in the double indirect block and this block number of the double indirect block is stored in the i node of the file. Similarly, you can keep doing this, you can have a triple indirect block and so on. So, normally file systems stop around a triple indirect block because you do not need to store files larger than that. So, note that this is not a symmetrically hierarchical structure like a page table. A page table everything was two levels in the two level page table to access any virtual address any page you had to go through two levels. But here it is not like that. The first few block numbers of a file you can get by directly from the i node. Then the next few block numbers you will have to do one hop. The next few block numbers you will have to do two hops, then three hops and so on. So, why is this hierarchical structure? Because accessing a file may require multiple disk accesses and it is very slow and therefore, if most files are just small, you want to avoid so many disk accesses. You want to avoid multiple disk accesses even for small files. So, small files I will try to fit them into the direct blocks as much as possible. Only for larger files the overhead will increase. So, that is the reason why this i node is somewhat of a asymmetric hierarchical structure unlike a page table. And as with any multi-level indexing structure accessing a file now requires multiple disk accesses. So, every time you want to read some data block of a file, first you have to get the i node. From there maybe read multiple other blocks and then finally know the block number that you want of the file and then read that disk block. So, your overhead has increased due to this i node structure. And this i node also imposes a certain limit on your maximum file size. As you can see, there is only so many data block numbers of a file you can store in the i node and that limits your file size. For example, if your i node has k direct blocks and a single indirect block that can store n other block numbers and a double indirect block that can store n single indirect blocks, a triple indirect block and so on. Then what is the maximum file size that you can keep track of in your i node? You can remember the first k direct blocks, then you can remember n indirect blocks that is the block numbers which are stored in the single indirect block. Then you have you know n single indirect block each of which has n block numbers. So, therefore, from the double indirect block you can store n squared block numbers, then from the triple indirect block you can store n cubed block numbers. So, this will be the maximum size of the file you can keep track of. Once your file size exceeds these many blocks, then there is no more space in your i node available in order to store the block number of your extra data in the file beyond these many blocks. If you need more blocks, there is no place to store the block number in your i node therefore, you cannot keep track of the file anymore. Therefore, there is a limit on the file size. Similarly, there could be limits on you know depending on how many i nodes you have, how many files you can have in your system what is the size of the disk that you can manage all of these based on how your file system is structured, how these metadata data structures are structured based on that there is certain limits on various file size and disk size and so on in any file system and different file systems have different limits because their data structures are different. So, next we come to directories. So, what is a directory? You all know what is a directory which is a collection of files. But in Linux like operating system, the directory is also treated like a special kind of file. It is not any separate entity. It is also a file just that it is a file which contains information about other files. It is a special kind of file which contains information like the names of all the files in that directory and their i node numbers. So, the directory if you look at if you treat the directory as sort of a text file or something as a regular file what you will find inside the directory is a file name and an i node number. You know file name, i node number, file name, i node number, sub directory, i node number. In this is what you will find inside a directory if you were to read it like a regular file. So, that therefore the directory is also a file. It will also have an i node number. It will also have an i node and all these contents of the directory will also be split into blocks spread all over the disk and the i node of the directory will keep track of all of these data blocks of a directory. So, it is treated like a file and the file type in the i node will indicate is it a regular file? Is it a directory kind of a special file? All of that is indicated and the i node of a directory keeps track of all these data blocks of a directory. And how do you store these file name to i node number mappings in the directory data blocks? You can store it in any format. You can say I will have fixed size records, you know there is a fixed size record that has the file name and i node number, another fixed size, another fixed size. You can store it as fixed size records, you can store it as a link list, you can store it as you know a binary search tree sorted by the alphabetically sorted by the file name. There are many different ways in which you can store this file name to i node number mapping in a directory. So, if you want to find a file in a directory, how do you do that? So, there is the i node of the directory itself that has information about all these data blocks of the directory. So, you will first fetch the i node of a directory and inside that i node of the directory you have all these data block numbers of the directory, you will locate the data blocks, you will read the data blocks of the directory and inside those data blocks you will find all of these records of a file name, its i node number, file name, its i node number, all of that information you will find inside the data blocks of the directory and then you will search through this information for the particular file you want. And once you find your file you know it is iNode number and from the iNode number of a file then you know the information about the data blocks of the file itself and then you can proceed to access the file. In this way the directory helps you locate the information about a particular file. And note that the search for the file name in a directory will depend on how the directory is storing these records, is it storing them as fixed size records, link list, search, tree. So depending on that you are searching for this file the logic will be different inside a directory. But the basic concept is as follows a directory is nothing but a special file that has mappings between the file names and their iNode numbers so that you can locate these iNodes of a file when you need to. And this directory this is the data blocks of a directory, every directory also has an iNode which has pointers to these data blocks. And this directory is iNode, this number will be there in its parent directory. The parent directory will keep track of the iNode number of a subdirectory. So now next let us understand path names. So what are path names you all know what path names are in any file system there is some path name like you know slash home slash foo slash a.txt this is sort of in a in the directory tree in the root file system starting with the root directory this path name helps you locate a particular file, a file is identified by its path name. Now every time you want to open or access a file in any way you need to know its path name so that you can find out more information about the file. So if you know the path name how do you find out the iNode number of the file it is as follows. You will first start with the root directory you will know the iNode number of the root directory from that you will get all the data blocks of the root directory. And in the data blocks of the root directory you have information like this home sub directory some others sub directory what their iNode numbers are you know those iNode numbers from this iNode number of the home directory you get its data blocks and inside the home directory there are many other directories there like the foo directory and you will get the iNode number of the foo directory and in the foo directory you have many files like you know a.txt and you know its iNode number and from this iNode number you will get the inode of a.txt and in that inode you have the data block numbers of a.txt you can access the file. So this is called recursively traversing the path name of a file in order to get to the information in the file. So you start with the root and for every element you will read the directories data blocks, look up the next element in the path name, retrieve its inode number and again repeat again read the next level its inode, its data blocks and the next level you find out its inode, its data blocks you keep repeating this process until you reach the end of your path name at which point you have the inode number of the file that you want from that inode number you will get information about all the data blocks of a file. So this is how you traverse a path name to find out more information about the file like its inode number and its data blocks. So now any file system has a certain layout on disk there are all of these things you know inodes and directories and everything and all of these are laid out, organized on disk in a certain way. So every hard disk if you look at it it will have you know a large number of data blocks which store you know the data of files as well as directories you know even directories need data blocks to keep track of file name to inode number mapping.  So what is a bitmap? You have one bit indicating 0 or 1 is the block on disk free or not you have that information that is called a bitmap. So you have all of these things stored on the hard disk and then there is one block the first block of the file system is called the super block which basically has information of this layout itself. The super block will say okay the first few blocks contain the bitmaps the next few blocks contain the inodes that next few blocks contain the data blocks all of this organization this information is stored in the super block. So anytime you want to understand how a file system is organized on disk you start with the super block read information about all the other organization in the super block and then you can access the rest of the file system and how is free space managed we have seen one way is the free list which is you remember you store the free block numbers as a list and the first free block number you remember in say your super block or somewhere and in this first free block you store the block number of the next free block in this free block you store the block number of the next free block and so on you can maintain like a free list like this or you can store a bitmap as we have discussed above you maintain one bit of information about each disk block that will tell you is that disk block free or is it in use by some file or some directory or something. So in this way you will manage the free space on a disk and this free space information these bitmaps are also stored on the hard disk and when you format a hard disk if you say you must have heard the term formatting a hard disk what does it mean it simply means laying out this information on the disk in a specific format and different file systems will have different layouts different you know data structures for all of these things and therefore the formatting also will be different. So next is the in memory data structures so all of this is on disk for a file system on disk you have data blocks you have inodes you have bitmaps you have a super block all of this is on the hard disk pertaining to a file system. Now a file system also in memory when the OS is running when the system is running in memory also it has a few data structures to keep track of and what are they when a file is opened and when it is being used to read and write you will basically take the inode from disk and you will keep a copy of it in memory in a cache that is called the in memory inode why is this done because when you are reading writing a file you need to know which is the first block number second block number you need to know a lot of information about the file in every time going to the disk to access the inode is a little bit suboptimal therefore to speed things up you will bring the inode into memory for the duration that the file is opened and in use that is the in memory inode then you have a data structure called the open file table which is used to keep track of all the open files. So, this is a table it has one entry for every file that is opened and this entry contains you know say the pointer to the in memory inode you know the inode number or various other pieces of information the other piece of information is the offset. Remember that in a previous lecture we have discussed when you read a file you read it as a stream of bytes if you first read 64 bytes the next time you read you will get the next 64 bytes. So, you have to remember the offset in a stream of bytes until which point have you read. So, that offset is also kept track of in the open file table. So, this open file table has the pointer to the in memory inode things like offset and a few other things all of this information is stored in the open file table and in addition to this open file table you have what is called the file descriptor array. So, this open file table is a global data structure there is one for all processes in the system whereas this file descriptor array is a per process array of information about the files that are open for this particular process and this is part of the PCB. The PCB is where you keep track of all information about a process the file descriptor array is also part of the PCB and this file descriptor array for every file that is open the info the pointer to this open file table entry will be stored in this file descriptor array. So, that this index in this file descriptor array this is what is returned to you when you open a file. So, when you open a file the inode is brought into memory and open file table entry is created and the pointer to this open file table entry is stored in the file descriptor array and which index is at the 012 whichever index in the file descriptor array you have stored this information that is returned to you as a file descriptor or a file handle. And in the future for any operation on the file you provide this handle and from this handle you follow the pointers you will reach the inode of the file you have all information about the file readily available for you ok. So, in the next lecture we are going to see how all of these data structures are used when we open a file read a file write a file and so on we will come to that in the next lecture. And one final in memory data structure is the disk buffer cache. So, all the blocks of a file that you read from disk recently all of them are cached in a least recently used cache called the disk buffer cache. So, these are all the important data structures of course different file systems more complicated real life file systems may have more or complex different data structures than this, but this is a basic idea for a simple file system. And one subtlety I would like to point out about the open file table is that every time you open a file with the open system call you will have a new entry in the open file table and a new entry in the file descriptor array. So, suppose there is a file that is opened by two different processes then the inode of the file will be common, but if process p opens a file it will create a separate open file table entry which is pointing to this inode. If process q opens the file it will also create a separate open file table entry that is also storing a pointer to the same inode. Similarly, process p will have it is own file descriptor array that has a pointer to the open file table entry process q will have it is own file descriptor array that has a pointer to its open file table entry. Why do we have this? Why do we have different open file table entries? This is because the files when they open when different processes open a file the offsets at which they are reading they are independent. If process p reads 64 bytes then process q will start at the beginning it will not continue where p left off therefore you need to keep track of different offsets therefore you will have different open file table entries. With the exception that when the parent folks a child process at that point if this is process p and it has forked a child c then both this parent and the child share the same offsets of the open files that is they will both point to the same open file table entry and when one of them reads or writes that offset is reflected in the other child. So, this is the only time where different processes will use the same open file table entry otherwise different processes open the same file also they will have separate open file table entries and they will read the file as independent streams. And in the case of the parent and child of course this is a little messy therefore it is usually better if one of them closes their file and the other continues to use it. So, that is all for this lecture. In this lecture we have introduced the concept of what happens in the file system of an operating system we have introduced the data structures like open file tables, i nodes and so on. In the next lecture we are going to continue our discussion on how the file system calls are implemented using these data structures. And a small exercise for you is as I have said there are many different file systems in use in modern systems. So, take a look at your computer, your desktop or laptop find out more about what file system is it running, what is the name of the file system, what are some of its differentiating characteristics. You might want to just read up a little bit about the different types of file systems available today. Thank you all that is all I have for this lecture. Let us continue this topic in the next lecture. Thank you.