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June 08, 2008

If Houses Grew Like Hard Drives

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Every once in awhile I like to throw out some thought provoking analogies and this week’s posting is actually quite amusing (well… I think so).  The question is, “what if the cost per square foot of a residence decreased at the same rate as the cost of a megabyte of storage in a typical hard drive”?  How big of a house could you buy today?  This also sparks another question, “if the same rate of energy efficiency improvement of hard drives (by space) applied to an average home (in the U.S.), how much power would you use per month”?

To answer the first question, we need some base lines.  In 1983 I was designing a computer system that required a hard disk drive.  We ordered a 5¼” full bay height unit made by Control Data (which was compatible with the Shugart ST-506 drive – the first 5¼” drive). When it arrived in our lab, we eagerly unpacked the drive, placed it on one of the benches and called all the other engineers into the lab to see it.  We all marveled at this amazing piece of hardware which weighed in at about 4 ½ pounds and could fit in your hand. The total unformatted capacity was 5 megabytes (a megabyte is referred in this post as 10^6 bytes for simplicity) and we all thought, “What would anyone ever do with that much storage capacity”? In a world where 16KB of main memory was a bunch, this seemed unbelievable! Also, this predated integrated drive electronics (IDE) so the disk controller was a large circuit card loaded with components to read from and write to the disk.  Those were the days!

At the time (and my memory is fading) the hard drive cost us roughly $1000 US.  Around the same time, I (and the bank) purchased my first home – an 1100 square foot condominium for $72,000 US.  If you adjust for inflation since July of 1983 (roughly 115%), today the hard drive would cost about $2150 US which calculates out to a cost per megabyte of $430 US. The condo would cost roughly $155,000 US today (unadjusted for increased material cost due to supply) which calculates out to about $141 US per square foot.  We’ll use these numbers for our base lines.

Today, a 1 terabyte drive (200,000 times more capacity than my 1983 vintage 5 megabyte drive) was advertised at just under $200 US.  That calculates out to $0.002 US or 2/10ths of 1 cent US per megabyte.  This equates to roughly a 215,000 times improvement in storage capacity per dollar.  Now if housing costs had done the same thing since 1983, today 1 square foot of residential space would cost roughly $0.00066 US per square foot.  You could purchase the equivalent space of the Empire State Building for around $1800 US (the Empire State Building would probably be a bit more since it’s considered commercial property and is located in Manhattan).

The more interesting view of this comparison is stated in question 2.  That is, “if the same rate of energy efficiency improvement of hard drives (by space) applied to an average home (in the U.S.), how much power would you use per month”?  We know from the above calculations that over the period of the last 25 years, there has been a 200,000 times improvement in storage capacity and a decrease in the power consumption.  The 1 terabyte drive uses roughly 38W worse case compared to the early ST-506 drives which consumed about 27W nominally (60W worse case).  For this discussion, let’s use the worse case numbers.  The vintage 5 megabyte drive consumed 12 watts per megabyte of storage.  The modern 1 terabyte drive consumes about 38 microwatts per megabyte which is roughly a 300,000 times improvement in energy efficiency.  A typical US home uses about 900 kilowatt-hours per month.  If we applied the same efficiency improvements to an average US household, the home would consume only 3 milliwatt-hours per month!  Disregarding the voltage and frequency conversion losses, this “modern” house could run off of a single AA battery for over a month!

When you considerer that today, manufacturers and consumers are very conscious about the amount of power a product consumes, the electronics industry has actually been making extremely large improvements over the last 25 years.  If you wanted to build a 1 terabyte drive out of the old ST-506 units, the array would draw over 8 megawatts (not including the controller power consumption and air conditioning) and occupy 17,300 cubic feet – the equivalent of a 2000 square foot home stacked floor to ceiling. Today a terabyte of storage fits in your hand and draws less than one of the original 5 megabyte drives –amazing!

If you’d like to comment on my post, please drop me either an email or comment on this blog – I’d love to post your story as well.  Till next time…