Talk:Direct-access storage device: Difference between revisions

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Really ought to create a 'data cells' page that should in turn link to Early_IBM_disk_storage#IBM_2321 instead of that link being in the See Also of this page. Cpeel (talk) 21:33, 19 May 2008 (UTC)[reply]

There is no "random" access method, and indexed isn't the same as random in any case. This omits partitioned, which is a special case. Peter Flass (talk) 19:38, 24 February 2012 (UTC)[reply]

Seems to me that random access is similar to what IBM usually calls direct access. Gah4 (talk) 04:30, 14 September 2017 (UTC)[reply]

I hated this definition "any secondary storage device which has relatively high access time relative to its capacity." If nothing else it should be fast access time. I'm changing it to paraphrase the IBM manual. Peter Flass (talk) 13:36, 23 December 2013 (UTC)[reply]

I think the paraphrase is almost as bad. "Direct" was coined by IBM to distinguish between "Random" as in core and "Sequential" as in tape; slower than core but faster than tape. The current paraphrase misses the speed point and I suspect is a way after the fact attempt to define without much knowledge of history. I'll look for a better source. Tom94022 (talk) 06:34, 14 September 2017 (UTC)[reply]

The access methods are responsible for blocking and deblocking logical records as they are written to or read from external media. I thought that for BSAM, the user program does deblocking, while QSAM does it for you. Gah4 (talk) 04:32, 14 September 2017 (UTC)[reply]

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If I remember my days with IBM jargon correctly, DASD would be "detachable asynchronous storage device".

Detachable, because it was a separate cabinet, and asynchronous, because it was NOT sync'd to the processor clock for operation. 134.247.251.245 (talk) 13:50, 22 October 2019 (UTC)[reply]

"in which "each physical record has a discrete location and a unique address". This is certainly not true with modern storage subsystems with deduplication built-in, because there files can share identical blocks of data with other versions of the same file, or even with completely different files where duplicate blocks were found to exist. Storage subsystems keep their own records, and copying a file simply creates a new pointer to the same data. Only when the "new" file gets changed, some blocks are newly assigned, containing those changes, and become part of the second file, but not of the first one. The computer normally has no access to the file structure in a storage subsystem, so all of this is unnoticed by the computer. 134.247.251.245 (talk) 14:43, 22 October 2019 (UTC)[reply]