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50th Anniversary of invention of disk drives 4590

Anne & Lynn Wheeler

I don't think they were very popular. Drums were a "compromise" between the high capacity of disk and the high speed of core. Since drums had fixed heads over each track they were faster, indeed, the IBM 650 and other small machines of the 1950s used drums as the sole main memory. I believe drums were invented by ERA (originally a secret firm* but then part of Rem Rand Univac**) in the late 1940s and quite popular in that era.

50th Anniversary of invention of disk drives 4591
there was another "comprise" between disks and high speed core for 360s. disks (drums, datacells, etc) were referred to as "DASD" (direct access storage device) ... more specifically "CKD" DASD (count-key...
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*Engineering Research buttociates, not to be confused with the Electric Railroaders' buttociation.

** "Dits to bits" says the orig Univac and ERA efforts weren't synchronized-coordinated adequately, a weakness by Remington Rand.

50th Anniversary of invention of disk drives
Michael Black ZX Spectrum had so-called microdrives - endless loop tapes: 1993 is pretty late, but not unconceivable - during the 1980s, hard drives were a luxury on most...

On our modest Univac 90-30 (used S-360 architecture) we had 3330 equivalents and could have the machines to ourselves for testing. I submitted two batch jobs that both went against the same file. The disk heads flew back and forth greatly vibrating the disk drive like an overloaded washing machine. When I ran the jobs singly the heads were able to stay in one position and back to back was faster than both at once.

As an aside, having exclusive control of the machine enabled me to run benchmark tests of various programming techniques. I found using binary (COMP SYNC) for subscripts significantly improved performance over plain USAGE DISPLAY fields. COMP-3 (packed decimal) helped a little, but binary was needed. I concluded the convert-to-binary and reverse instructions were rather slow and should be avoided. I then tested the above using INDEXED BY fields. That was only a slight improvement over binary fields.

It amazed me how many programmers didn't understand the significance of that.

In those days sometimes programs would be generic written in COBOL for widespread use. But IBM S-360 architecture was different than word architectures used on other machines and performance and usage didn't mesh well. IBM required a carriage control character for printing, the others didn't. IBM wouldn't allow spaces in a numeric field, but the others did. IBM had packed decimal and needed it for performance, the others didn't. Indeed, there were differences between COBOL for IBM OS and DOS.

I hated working with generic programs which I had to do for several employers to this day. They had all sorts of features most of which weren't necessary but greatly added to bloated code and confusion. One system had very short data field names in COBOL even though 30 characters were allowed.

It blows my mind at how cheap disk space is these days. It used to be expensive and scarce, tightly allocated and controlled. They back up data on other disks instead of on tape (cart).

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50th Anniversary of invention of disk drives 4591

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50th Anniversary of invention of disk drives 4589