10 Aug
2013
10 Aug
'13
10:58 a.m.
-----Original Message-----
From: Mark S Waterbury [mailto:mark.s.waterbury at bellsouth.net]
Sent: Friday, August 09, 2013 7:22 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Track Sizes etc. (was Re: IBM 4331 (was Re: FPGAs))
Hi, Jay:
As far as I know:
IBM 2311 DASD had 3625 bytes per track, with 10 tracks per cylinder
IBM 2314 DASD had 7284 bytes per track, with 20 tracks per cylinder
IBM 3330 DASD had 13030 bytes per track, with 20 tracks per cylinder
IBM 3350 DASD had 19069 bytes per track, with 15 tracks per cylinder
<snip>
I believe the bytes per track listed above are formatted with an IBM R0
(Record 0). The actual number is larger, e.g. the 3330 had precisely 13,440
unformatted bytes per track (revolution) which in the IBM format would
support one R1 per track of up to 13,030 bytes (13030/13440=97%
utilization). Because of the headers and gaps, utilization went down as the
record size got smaller. Other computer systems used other formats to have
other capacities per track, e.g. DEC RP05 used 22 512 byte sectors/track
(84% utilization but higher than IBM's with a record size of 512). The 2311
and 2314 were not as precise due to the rotation speed variation. The 3350
was precise at somewhere near 19,960 unformatted bytes/track (BTW the CDC
SMD number was 20,160). Back then storage was expensive and utilization was
important.
And, to address comments by Rich, responding to
comments by Christian,
as I recall, no operating systems then extant had yet come up with "a
better way" to deal with "disk geometry" (as it was called). So, it was
not only IBM operating systems that seem "primitive" by today's standards.
AFAIK, it was not until FBA disks became popular, and in the 1980s, with
the emergence of the SCSI standards, when companies began to figure out
that it was much easier to just deal with a disk unit as a sequence of
addressable blocks, ...
<snip>
AFAIK, all disk drives prior to the IBM 2311 and S/360 had fixed block sizes
(FBA) and most if not all systems (BUNCH and mini's) continued with FBA
while IBM continued CKD into the 90s. The IBM Channel and CKD architecture
was an improvement in that it allowed the block size to be optimized to the
application (storage was expensive) and thru use of the Key field allowed in
channel processing (peripheral processing) that improved overall system
performance. So in a certain sense FBA is back to the simpler past :-)
What killed CKD architecture was 1) the need for ever increasing distance
between the DASD and the system made the gaps between the fields consume too
much space and 2) disk storage became so inexpensive block size optimization
wasn't worth the cost.
Credit for commercializing FBA should include DEC for its DSA (Digital
Storage Architecture) beginning circa 1976 which was its response to the
varying block sizes across its several product lines. The first DEC DSA
products were the UDA50/RA80 in 1981
Tom