Talk:Hard disk drive/Archive 16

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355 Capacity in modern terms

As an added complication, the similar 355 stored data as decimal digits; a character was stored as a pair of digits, with code points from 0 to 99. The capacity was 6 million digits or 3 million characters; how would you express that in 8-bit bytes? Shmuel (Seymour J.) Metz Username:Chatul (talk) 21:50, 9 September 2014 (UTC)

Do we know how each digit was stored? — Dsimic (talk | contribs) 22:30, 9 September 2014 (UTC)

We do not. There is no known document comparable to the 305 CE Manual. The best I know of is the 650 Manual of Operation. What is disclosed is that it is has a full track data organization, reading and writing 60 contiguous words of 10 digits each with a two word gap between the end of the data and its beginning, see figure 5 on page 18. There is no track to track orientation, a read starts with the sensing of the gap while a track write operation starts at any location with writing of the gap. There is no mention of parity; it does say that as each digit is read it is checked for validity. Now for some speculation and/or original research:

• If as is likely it uses a bi-quinary coded decimal code which in modern terms is a self checking 7 bit channel code then no parity would be required.
• It would be possible to decimal pack 6 million decimal characters into 3 million bytes so one way to look at the capacity is it would take 3.002368 MB of modern storage using 4k sectors to store the contents of a 355.

Bottom line - I know of no reliable source that allows us to determine the 355 capacity in modern terms. Tom94022 (talk) 01:11, 10 September 2014 (UTC)

Thank you very much for the explanation! This is really interesting, and such a data layout resembles more of a basic file system, rather than "bare" data storage as we have it in modern HDDs. Asking "how much of a modern HDD do we need to replace a 355" is pretty much like asking "how much of btrfs data structures do we need to replace a CP/M-formatted floppy disk", what wouldn't be easy to answer at all. — Dsimic (talk | contribs) 04:55, 10 September 2014 (UTC)

"A HDD" vs. "an HDD", and some barebones

Hey Luigi.a.cruz! Just wanted to discuss latest few edits on this article, which are well summarized in this edit. Regarding whether "a" or "an" should be used with "HDD", the decision is based on how something is pronounced, not on how that's written. As "HDD" is pronounced as "aitch-dee-dee", thus it starts with a vowel, "an" is to be used; a good example is "an hour", as "hour" is also pronounced with opening vowel.

Regarding the "IDE-based barebone", what's the "barebone" supposed to mean in the HDD context? When a "barebone" is mentioned to someone who deals with PCs, it usually refers to computers sold with just a motherboard, PSU and case – but how does that make a special case for HDDs? At the same time, for the "Past and present HDD form factors" summary table we want "cherry-picked" best samples, so there's pretty much no need to explain the size limits for various device classes.

Please advise. — Dsimic (talk | contribs) 20:55, 5 September 2014 (UTC)

Agree with Dsimic. "IDE" (or rather "PATA" as it should be called) is not a separate form factor (for the purposes of this table, anyway) and does not need to be mentioned here. (If it is, then I will insist on additional efn's for earlier PATA versions that only supported 128 GiB, for SCSI and SCA, etc.) Jeh (talk) 17:26, 6 September 2014 (UTC)

Agree, we do not distinguish other obsolescent or obsolete interfaces such as SCSI, ST412, SMD, etc. I recommend we remove all the added PATA references. Tom94022 (talk) 23:33, 8 September 2014 (UTC)

BTW, "HDD" is pronounced "haitch-dee-dee" in some versions of British English, and therefore might be proceeded by "an" instead of "a". But this article is in American English, so "a HDD" is correct here. --A D Monroe III (talk) 17:21, 16 September 2014 (UTC)

Hm, why "a HDD", when the American English pronounciation starts with a vowel? Guess that was a typo? — Dsimic (talk | contribs) 02:28, 17 September 2014 (UTC)

"An HDD" is the correct American form. "HDD" starts with a vowel sound, "aitch". Therefore we use "an". I don't understand why ADM III would say otherwise. Jeh (talk) 04:34, 17 September 2014 (UTC)

Oops! Typo. I meant "a HDD" for Brit English, and "an HDD" for Amer English, which is for this article. Sorry about that. (Can we get off dumb ol' text and switch Wikipedia to full audio anytime soon?) --A D Monroe III (talk) 22:05, 17 September 2014 (UTC)

Thanks for the clarification. Speaking about text vs. audio, hm, they both have pros and cons. :) — Dsimic (talk | contribs) 03:45, 18 September 2014 (UTC)

An IBM 305 is not an IBM 650

The discussion of the capacity of an IBM 350 connected to an IBM 305 RAMAC repeatedly conflates the 305 with the 650. They are different machines, with different data representations.

The IBM 650 had signed 10 digit words, with each digit represented in bi-quinary, and represented character data as pairs of decimal digits. The 305 represented characters as 6 bits plus parity. In both cases the character coding used was influenced by the coding on the Hollerith card. Similarly, the formatted capacity of the 350 disk is not in the same units as the formatted capacity of the 355; the first is in characters (six bits plus parity) while the second is in signed 10-digit words. The relevant manuals are all available at http://bitsavers.org/pdf/ibm/305_ramac/ and http://bitsavers.org/pdf/ibm/650/. Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:44, 18 September 2014 (UTC)

Bad source?

The reference to the size and capacity of the IBM 350 (here) actually references Wikipedia itself. Surely this can't be used as a reliable source. --Lewis Hulbert (talk) 14:46, 19 September 2014 (UTC)

Good point, the reference will have to change. Thanks Tom94022 (talk) 16:52, 19 September 2014 (UTC)

Although the wording is almost exactly to what's written in the article. Perhaps an unsourced copy/paste? --Lewis Hulbert (talk) 18:56, 19 September 2014 (UTC)

Another good point. How about Oracle magazine as a reliable source not obviously relying upon Wikipedia? Tom94022 (talk) 21:06, 19 September 2014 (UTC)