Disk Capacity....

From: Paul Koning <pkoning_at_equallogic.com>
Date: Tue Jul 13 08:36:19 2004

>>>>> "David" == David V Corbin <dvcorbin_at_optonline.net> writes:

 David> Kind of off the wall, but the issue came up in a discussion
 David> here, and want to get some solid numbers...

 David> June 2004 Disk Capacity [IDE 5.25] = 250 Gig [approx] June
 David> 2004 Disk Surface Area (total) = ??? Sq inches Average
 David> Capacity per Sq Inch = ???

Today's drives are usually 3.5 inch enclosure size. The generation
that goes up to 250 GB has about 80 GB per platter; coming up any day
now is 120 or so GB/platter.

I'm not sure about the platter size. Call it 3 inch diameter for a
rough guess, that makes perhaps 10 square inches once you take the hub
out. So that means 8 GB per square inch.

 David> RP06 Disk Capacity = ??? [100+ MB] RP06 Disk Surface Area
 David> (total) = ??? Sq inches Average Capacity per Sq Inch = ???

RP06: 176 MB, 19 surfaces, 14 inch diameter, so maybe 100 square
inches per surface, so about 0.1 MM per square inch.

 David> The above numbers would yield a hypothetical capacity for a
 David> disk (pack) this size (and number of platter) of an RP06.....

 David> This was brought up in part by seeing a row of 8 RP-06 drives
 David> and marveling at the size [floor space] required for just
 David> about 1 Gig of disk....

Sure, and the RP06 was pretty impressive in its day. Go back a bit
more to the RK05: 2 surfaces, somewhat bigger than the RP06 (smaller
hub) -- but let's ignore that. 2.4 MB capacity. So that gives 12 kB
per square inch.

Back a bit further... the CDC 6603 (early 1960s). 100 MB per
cabinet. (This is a fixed media, moving head drive.) 32 surfaces, so
that's 3 MB per surface. Not sure how big those platters are -- 25
inches perhaps? If yes, that would make about 400 square inches per
platter, so about 7.5 kB per square inch.

Hm, not much less than the RK05. The 6603 is also MUCH faster because
it records data 12 bits parallel (using 12 heads simultaneously) for a
transfer time per sector of about 500 microseconds. That's about
1 MB/s (322 12-bit words per sector) -- compare with RK05 at 6
microseconds per byte if I remember right, so 1/6th the speed about 8
to 10 years later than the 6603...

Then again, in fairness, the 6603 looks like a 6 foot high by perhaps
8 feet wide rack... and probably cost 20x to 50x an RK05/RK11 combo.

    paul
Received on Tue Jul 13 2004 - 08:36:19 BST