Sabtu, 21 April 2012

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number5150, and was introduced on August 12, 1981. It was created by a team of engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division inBoca Raton, Florida.
Alongside "microcomputer" and "home computer", the term "personal computer" was already in use before 1981. It was used as early as 1972 to characterize Xerox PARC'sAlto. However, because of the success of the IBM Personal Computer, the term PCcame to mean more specifically a microcomputer compatible with IBM's PC products.




Desktop sized programmable calculators by Hewlett Packard had evolved into the HP 9830 BASIC language computer by 1972, with IBM's releasing its own IBM 5100 in 1975. It was a complete system programmable in BASIC or APL, with a small built-in CRT monitor, keyboard, and tape drive for data storage. It was also very expensive — up to $20,000 USD. It was specifically designed for professional and scientific problem-solvers, not business users or hobbyists.[1] When the PC was introduced in 1981, it was originally designated as the IBM 5150, putting it in the "5100" series, though its architecture was not directly descended from the IBM 5100.
The original line of PCs were part of an IBM strategy to get into the small personal computer market then dominated by the Commodore PETAtari 8-bit familyApple IITandy Corporation's TRS-80s, and various CP/M machines.[2]
New products at IBM typically required about four years for development. The company recognized that to compete with other personal computers it needed to develop its offering much more quickly.[3] Rather than going through the usual IBM design process, a special team was assembled with authorization to bypass normal company restrictions and get something to market rapidly. This project was given the code name Project Chess at the IBM Entry Systems Division in Boca Raton, Florida. The team consisted of twelve people directed by Don Estridge with Chief Designer Lewis Eggebrecht.[4] They developed the PC in about a year. To achieve this they first decided to build the machine with "off-the-shelf" parts from a variety of different original equipment manufacturers (OEMs) and countries. Previously IBM had always developed its own components. Secondly for scheduling and cost reasons, rather than developing unique IBM PC monitor and printer designs, project management decided to utilize an existing "off-the-shelf" IBM monitor developed earlier in IBM Japan as well as an existing Epson printer model. Consequently, the unique IBM PC industrial design elements were relegated to the system unit and keyboard.[5] They also decided on an open architecture, so that other manufacturers could produce and sell peripheral components and compatible software without purchasing licenses. IBM also sold an IBM PC Technical Reference Manualthat included complete circuit schematics, a listing of the ROM BIOS source code, and other engineering and programming information.[6] IBM announced the PC on August 12, 1981. Six weeks later at COMDEX Fall, Tecmar had 20 PC products available for sale. These products included memory expansion, IEEE-488, data acquisition, and PC Expansion chassis[7][8][9][10] .[11] Pricing for the IBM PC started at $1,565 for a bare-bones configuration without disk drives.[12]
At the time, Don Estridge and his team considered using the IBM 801 processor (an early RISC CPU) and its operating system that had been developed at the Thomas J. Watson Research Center in Yorktown Heights, New York. The 801 processor was more than an order of magnitude more powerful than the Intel 8088, and the operating system more advanced than the DOS 1.0 operating system fromMicrosoft, which was finally selected. Ruling out an in-house solution made the team’s job much easier and may have avoided a delay in the schedule, but the ultimate consequences of this decision for IBM were far-reaching. IBM had recently developed the Datamasterbusiness microcomputer, which used an Intel processor and peripheral ICs; familiarity with these chips and the availability of the Intel 8088 processor was a deciding factor in the choice of processor for the new product. Even the 62-pin expansion bus slots were designed to be similar to the Datamaster slots. Delays due to in-house development of the Datamaster software also influenced the design team to a fast-track development process for the PC, with publicly available technical information to encourage third-party developers.[13]
Other manufacturers soon reverse engineered the BIOS to produce their own non-infringing functional copies. Columbia Data Productsintroduced the first IBM-PC compatible computer in June 1982. In November 1982, Compaq Computer Corporation announced theCompaq Portable, the first portable IBM PC compatible. The first models were shipped in March 1983.
Once the IBM PC became a commercial success, the product came back under the more usual tight IBM management control.[citation needed] IBM's tradition of "rationalizing" product lines, deliberately restricting the performance of lower-priced models in order to prevent them from "cannibalizing" profits from higher-priced models, worked against them.[citation needed]

[edit]IBM PC as standard

The success of the IBM computer led other companies to develop IBM Compatibles, which in turn led to branding like diskettes being advertised as "IBM format". An IBM PC clone could be built with off-the-shelf parts, but the BIOS required some reverse-engineering. Companies like Phoenix Software AssociatesAmerican MegatrendsAward, and others achieved workable versions of the BIOS, allowing companies like DELL, Compaq, and HP to manufacture PCs that worked like IBM's product. The IBM PC became the industry standard.

[edit]Third-party distribution

ComputerLand and Sears Roebuck partnered with IBM from the beginning of development. IBM's head of sales and marketing, H.L. ('Sparky') Sparks, relied on these retail partners for important knowledge of the marketplace. Computerland and Sears became the main outlets for the new product. More than 190 Computerland stores already existed, while Sears was in the process of creating a handful of in-store computer centers for sale of the new product. This guaranteed IBM widespread distribution across the U.S.


IBM Personal Computer
Ibm pc 5150.jpg
IBM 5150 PC
The IBM PC line
Model nameModel #IntroducedCPUFeatures
PC5150August 19818088Floppy disk or cassette[14] system
XT5160March 19838088First IBM PC to come with an internal hard drive as standard.
XT/3705160/588October 198380885160 with XT/370 Option Kit and 3277 Emulation Adapter
3270 PC5271October 19838088With 3270 terminal emulation, 20 Function Key Keyboard
PCjr4860November 19838088Floppy-based home computer, Infrared Keyboard
Portable5155February 19848088Floppy-based portable
AT5170August 198480286Faster Processor, Faster System Bus (6 MHz, later 8 MHz, vs 4.77 MHz), Jumperless Configuration, Real Time Clock
AT/3705170/599October 1984802865170 with AT/370 Option Kit and 3277 Emulation Adapter
3270 AT5281June 1985[15]80286With 3270 terminal emulation
Convertible5140April 19868088Microfloppy laptop portable
XT 2865162September 198680286Slow hard disk, but zero wait statememory on the motherboard. This 6 MHz machine was actually faster than the 8 MHz ATs (when using planar memory) because of the zero wait states


The most commonly used storage medium was the floppy disk, though cassette tape was originally envisioned by IBM as a low-budget alternative. Accordingly, the IBM 5150 PC was available with one or two 5-1/4" floppy drives or without any drives or storage medium; in the latter case IBM intended a user to connect his own cassette recorder via the 5150's cassette port. The cassette tape port was mechanically identical to, and located next to, the keyboard port on the 5150's motherboard. A hard disk could not be installed into the 5150's system unit without retrofitting a more powerful power supply, but an "Expansion Unit," a.k.a. the "IBM 5161 Expansion Chassis," was available, which came with one 10 MB hard disk and also allowed the installation of a second hard disk.[17] The system unit had five expansion slots, and the expansion unit had eight; however, one of the system unit's slots and one of the expansion unit's slots had to be occupied by the Extender Card and Receiver Card, respectively, which were needed to connect the expansion unit to the system unit and make the expansion unit's other slots available, for a total of 11 slots. A working configuration required that some of the slots be occupied by display, disk, and I/O adapters, as none of these were built in to the 5150's motherboard; the only motherboard external connectors were the keyboard and cassette ports. The simple PC speaker sound hardware was also on-board. The original PC's maximum memory using IBM parts was 256 kB, 64 kB on the motherboard and three 64 kB expansion cards. The processor was an Intel 8088 running at 4.77 MHz (4/3 the standard NTSC color burst frequency of 3.579545 MHz). (In early units, the Intel 8088 used was a 1978 version, later were 1978/81/2 versions of the Intel chip; second-sourced AMDs were used after 1983)[citation needed]. Some owners replaced the 8088 with an NEC V20 for a slight increase in processing speed and support for real mode 80286 instructions. AnIntel 8087 co-processor could also be added for hardware floating-point arithmetic. IBM sold the first IBM PCs in configurations with 16 or 64 kB of RAM preinstalled using either nine or thirty-six 16-kbit DRAM chips. (The ninth bit was used for parity checking of memory.) After the IBM XT shipped, the IBM PC motherboard was configured more like the XTs motherboard with 8 narrower slots[dubious ], as well as the same RAM configuration as the IBM XT. ( 64 kB in one bank, expandable to 256kB by populating the other 3 banks ).
Although the TV-compatible video board, cassette port and Federal Communications Commission Class B certification were all aimed at making it a home computer,[18] the original PC proved too expensive for the home market. At introduction, a PC with 64 kB of RAM and a single 5.25-inch floppy drive and monitor sold for US $3,005 ($ 7,682 in today's dollars), while the cheapest configuration (1565 US$) that had no floppy drives, only 16 kB RAM, and no monitor (again, under the expectation that users would connect their existing TV sets and cassette recorders) proved too unattractive and low-spec, even for its time (cf. footnotes to the above IBM PC range table).[19][20]While the 5150 did not become a top selling home computer, its floppy-based configuration became an unexpectedly large success with businesses.




The IBM Personal Computer XT/370 was an XT with three custom 8-bit cards: the processor card (370PC-P), contained a modifiedMotorola 68000 chip, microcoded to execute System/370 instructions, a second 68000 to handle bus arbitration and memory transfers, and a modified 8087 to emulate the S/370 floating point instructions. The second card (370PC-M) connected to the first and contained 512 kB of memory. The third card (PC3277-EM), was a 3270 terminal emulator necessary to install the system software for the VM/PC software to run the processors. The computer booted into DOS, then ran the VM/PC Control Program.[23][24]








The "IBM Personal Computer AT/370 was an AT with two custom 16-bit cards, running almost the exact same setup as the XT/370.



[edit]Next Generation IBM PS/2




Original IBM Personal Computer motherboard, IBM 5150. It has five 8-bitIndustry Standard Architecture slots, and two DIN connectors for keyboard and cassette interface.
The bus used in the original PC became very popular, and it was subsequently named ISA. While it was popular, it was more commonly known as the PC-bus or XT-bus; the term ISAarose later when industry leaders chose to continue manufacturing machines based on the IBM PC AT architecture rather than license the PS/2 architecture and its MCA bus from IBM. The XT-bus was then retroactively named 8-bit ISA or XT ISA, while the unqualified term ISAusually refers to the 16-bit AT-bus (as better defined in the ISA specifications.) The AT-bus is an extension of the PC-/XT-bus and is in use to this day in computers for industrial use, where its relatively low speed, 5 volt signals, and relatively simple, straightforward design (all by year 2011 standards) give it technical advantages (e.g. noise immunity for reliability).
Quadram Quadboard.
Intel 8086 and 8088-based PCs require expanded memory (EMS) boards to work with more than 640 kB of memory. (Though the 8088 can address one megabyte of memory, the last 384 kB of that is used or reserved for the BIOS ROM, BASIC ROM, extension ROMs installed on adapter cards, and memory address space used by devices including display adapter RAM and even the 64 kB EMS page frame itself.) The original IBM PC AT used an Intel 80286 processor which can access up to 16 MiB of memory (though standard DOSapplications cannot use more than one megabyte without using additional APIs.) Intel 80286-based computers running under OS/2 can work with the maximum memory.
The original system chips were one Intel 8259 programmable interrupt controller (PIC) (at I/O address 0x20), one Intel 8237 direct memory access (DMA) controller (at I/O address 0x00),and a Intel 8253 programmable interval timer (PIT) (at I/O address 0x40). The PIT provides the 18.2 Hz clock ticks, dynamic memory refresh timing, and can be used for speaker output;[28] one DMA channel is used to perform the memory refresh. Math co-processor 8087 at 0xF0. The IBM PC AT added a second, slave 8259 PIC (at I/O address 0xA0), a second 8237 DMA controller for 16-bit DMA (at I/O address 0xC0), a DMA address register (implemented with a 74LS612 IC) (at I/O address 0x80),[29] and a Motorola MC146818 Real-time clock (RTC) with Nonvolatile memory (NVRAM) used for system configuration (replacing the DIP switches and jumpers used for this purpose in PC and PC-XT models (at I/O address 0x70).[30] On expansion cards, the Intel 8255 programmable peripheral interface (PPI) (at I/O addresses 0x378 is used for parallel I/O controls the printer,[31] and the8250 universal asynchronous receiver/transmitter (UART) (at I/O address 0x3F8 or 0x3E8) controls the serial communication at the (pseudo-)[32]RS-232 port.


The original keyboard for the IBM 5150
The original 1981 IBM PC's keyboard at the time was an extremely reliable and high quality electronic keyboard originally developed in North Carolina for the Datamaster system.[33]Each key was rated to be reliable to over 100 million keystrokes. For the IBM PC, a separate keyboard housing was designed with a novel usability feature that allowed users to adjust the keyboard angle for personal comfort. Compared with the keyboards of other small computers at the time, the IBM PC keyboard was far superior and played a significant role in establishing a high quality impression. For example, the industrial design of the keyboard, together with the system unit, was recognized with a major design award.[5] Byte magazine in the fall of 1981 went so far as to state that the keyboard was 50% of the reason to buy an IBM PC. The importance of the keyboard was definitely established when the 1983 IBM PCjrflopped, in very large part for having a much different and mediocre Chiclet keyboard that made a poor impression on customers. Oddly enough, the same thing almost happened to the original IBM PC when in early 1981 management seriously considered substituting a cheaper and lower quality keyboard. This mistake was narrowly avoided on the advice of one of the original development engineers.
However, the original 1981 IBM PC 84-key keyboard was criticized by typists for its non-standard placement of the Return and leftShift keys, and because it did not have separate cursor and numeric pads that were popular on the pre-PC DEC VT100 series video terminals. In 1982, Key Tronic introduced the now standard 101-key PC keyboard. In 1984, IBM corrected the Return and left Shift keys on its AT keyboard, but shortened the 'backspace' key, making it harder to reach. In 1986, IBM changed to the 101 key enhanced keyboard, which added the separate cursor and numeric key pads, relocated all the function keys and the Ctrl keys, and the Esc key was also relocated to the opposite side of the keyboard.
Another criticism of the original keyboard was the relatively loud "clack" sound each key made when pressed. Since typewriter users were accustomed to keeping their eyes on the hardcopy they were typing from and had come to rely on the mechanical sound that was made as each character was typed onto the paper to ensure that they had pressed the key hard enough (and only once), the PC keyboard electronic "clack" feature was intended to provide that same reassurance. However, it proved to be very noisy and annoying, especially if many PCs were in use in the same room, and later keyboards were significantly quieter.

[edit]Character set


[edit]Storage media

[edit]Cassette tape


[edit]Floppy diskettes

Most or all 5150 PCs had one or two 5.25-inch floppy disk drives. These floppy drives were either single-sided double-density drives (SS/DD, a.k.a. SSDD), or double-sided double-density drives (DS/DD, a.k.a. DSDD). The IBM PC never used single density floppy drives. The drives and disks were commonly referred to by capacity, e.g. "160KB floppy disk" or "360KB floppy drive". DSDD drives were backwards compatible; they could read and write SSDD floppies. The same type of physical diskette could be used for both drives,[34] however to convert a 5.25-inch SSDD disk to a DSDD disk, it needed to be reformatted, at which point SSDD drives could no longer read it.
The disks were Modified Frequency Modulation (MFM) coded in 512-byte sectors, and were soft-sectored.[35] They contained 40 tracks per side at the 48 track per inch (TPI) density,[36]and initially were formatted to contain eight sectors per track. This meant that SSDD disks initially had a formatted capacity of 160 kB,[37] operating system was later updated to allow formatting the disks with nine sectors per track. This yielded a formatted capacity of 180 kB with SSDD disks while DSDD disks had a capacity of 320 kB.[38] However, the DOS /drives,[39] and 360 kB with DSDD disks/drives.[40] The unformatted capacity of the floppy disks was advertised as "250KB" for SSDD and "500KB" for DSDD ("KB" ambiguously referring to either 1000 or 1024 bytes; essentially the same for rounded-off values), however these "raw" 250/500 kB were not the same thing as the usable formatted capacity; under DOS, the maximum capacity for SSDD and DSDD disks was 180 kB and 360 kB, respectively. Regardless of type, the file system of all floppy disks (under DOS) was FAT12.

[edit]Fixed disks

20MB Seagate ST-225 with a controller card by Western Digital
The first IBM PC that shipped with an internal, fixed, non-removable hard disk was IBM's model 5160, the XT. As other IBM-compatible PCs started to appear, hard disks with larger storage capacities also became available. Space permitting, these could be installed into either the IBM PC's Expansion Unit, into PSU-upgraded PCs or into XTs. Adding a third-party hard disk sometimes required plugging in a new controller board, because some of these hard drives were not compatible with the existing disk controller. Some third party hard disks for IBM PCs were sold as kits including a controller card and replacement power supply. Finally, some hard disks were integrated with their controller into a single expansion card, commonly called a "Hard Card".

[edit]OS support

The IBM PC's ROM BASIC and BIOS supported cassette tape storage. DOS itself did not support cassette tape storage. PC-DOS version 1.00 supported only 160 kB SSDD floppies, but version 1.1, which was released nine months after the PC's introduction, supported 160 kB SSDD and 320 kB DSDD floppies. Support for the slightly larger nine sector per track 180 kB and 360 kB formats arrived 10 months later in March 1983. In addition to PC-DOS, buyers could choose either CP/M-86 or UCSD p-System as operating systems, as well as some flavors of SysV Unix. Due to their higher prices, they never became very popular and PC-DOS (a.k.a. IBM-DOS) or MS-DOS came to be the dominant operating system.

[edit]Serial port addresses and interrupts

COM PortIRQBase port address [Hex]

[edit]Original software





The IBM model 5150 Personal Computer has become a collectable among vintage computer collectors, due to the system being the first true “PC” as we know them today. Today these systems can fetch anywhere from $100 to $4500, depending on cosmetic and operational condition.[citation needed] The IBM model 5150 has proven to be very reliable and most systems, despite their age of 25 years or more, still function as they did when new.[citation needed]

[edit]See also