Talk:Interleaving (disk storage)

POV of article

As I understand it, disk storage interleaving improves overall system performance on slow computers by slowing down the data rate of a rotating storage device to less than the sustainable data rate of the slow computer to the point that there are no lost revolutions. The article seems oblivious to this point focusing instead on processing time. But it also lacks references to definitions of interleaving, so I will do some research and revise accordingly, with references. Tom94022 (talk) 16:44, 2 May 2013 (UTC)

Also, didn't early time sharing machines fast enough handle the data rate, still use interleaving to assure availability by forcing file transfer to be a block at a time, with the interleave space being available to other users? I seem to recall that is the way the first UNIX file systems operated. Again I need to do some research and will revise accordingly with references. Tom94022 (talk) 16:54, 3 May 2013 (UTC)

There is interleaving of sectors, variable length records, e.g., on CKD DASD, and words, e.g., on IBM 650. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 16:42, 6 February 2022 (UTC)

@Tom94022: The drum memory article covers both drum primary memory and drum auxiliary storage. While the later is block storage, the former is not. There is a WP:POV issue in the first sentence of the lead without the qualifying phrase and in drum memory. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:36, 24 February 2022 (UTC)

And drum memory is not disk storage which is the title of this article. Memory interleaving is well established so maybe that's where the reference should go. Reverting once more. Tom94022 (talk) 17:05, 25 February 2022 (UTC)

The Memory interleaving article is totally unrelated, as should be clear from first sentence. It describes parallel banks of DRAM, not interleaved placement of data on a rotating device.

The first sentence says "or core" so it is not exclusive to DRAM and there is no reason drum memory can't be added to an improved article. Who knows, perhaps they interleaved Williams tubes too. Tom94022 (talk) 00:21, 26 February 2022 (UTC)

The reason to not add drums to Memory interleaving is that nobody built a computer with interleaved addresses across multiple drums. As for Williams tubes, a common arrangement was to have one tube for each bit in a word. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:15, 27 February 2022 (UTC)

There is nothing about interleaving that is specific to disk, and to the best of my knowledge interleaving was used on drums before it was used on disks. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 19:13, 25 February 2022 (UTC)

FWIW,:::::

Magnetic drum units used as primary memory were addressed by word. Drum units used as secondary storage were addressed by block. (emphasis added)
— Drum memory

Perhaps there should be one article on all of interleaving in computing but right now we have two, one related to disk with is block interleaving and one related to memory which is word interleaving. So if Drum memory is to be added it seems more appropriate to add it to and improve the Memory interleaving article. Tom94022 (talk) 00:21, 26 February 2022 (UTC)

At one point, there was a page on interleaved memory and a page on interleaving that discussed interleaving in block storage and interleaving in error-correction codes. I saw that this was ridiculous as the two topics had little to do with one another, and moved the former to this page and the latter to error correction code § Interleaving. Interleaving is now a disambiguation page pointing to a bunch of forms of interleaving. So, no, there should not be one article on all of interleaving in computing. Guy Harris (talk) 01:30, 26 February 2022 (UTC)

I see several distinct uses of the term interleaving

ECC

Should be separate article

Multiple banks of RAM, e.g., core, DRAM

Memory interleaving

Interleaving of bits

Should be section

Replication

Should be section

Pad records

Should be section

Other

Should be section

The last three apply to both disk and drum and should be in the same article. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:15, 27 February 2022 (UTC)

(Speaking of the interleaved memory article, it should be about more than parallel banks of DRAM; interleaving dates back to the days of core memory, so a description of how interleaving works for other memory technologies probably belongs there, in the History section if nowhere else.)

Was any interleaving done on drum storage devices in the same fashion in which it was done on disk devices? This article appears to describe disk storage interleaving described that's done at the disk controller level, so that blocks that have sequential addresses within a track, as seen by software speaking to the controller ("speaking to the controller" here includes "constructing a channel program to tell the channel to speak to the controller"), are not physically sequential on the track. Was that done on drums as well? (Presumably interleaving done above the controller level could be done on any block storage device, including flash memory.) Guy Harris (talk) 19:31, 25 February 2022 (UTC)

Yes, the first machines with interleaved banks of memory used core. I don't know whether anybody used it on thin film.

I've only seen disk and drum interleaving done by the software. If there are controllers or drives that do interleaving transparently then perhaps there should be two articles. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 21:47, 25 February 2022 (UTC)

Track Interleaving

Track Interleaving to the best of my knowledge is a term invented for this article that refers to the well documented Cylinder concept where files are laid out to sequentially fill cylinders. As such Track Interleaving has no place in this article much less in Wikipedia. I'll do some research but in the absence of a reliable source I will revert. Tom94022 (talk) 15:02, 17 June 2013 (UTC)

I found no reliable source for Track interleaving but did find Cylinder so I reverted added material. Tom94022 (talk) 16:52, 19 June 2013 (UTC)

Wasn't this about sector mapping? Single-sided floppy formats use a "sector/track" logical to physical sector mapping (that is, they use up all sectors of one track before going to the next track). I'm not aware of any "track/sector" formats, but theoretically, they might have existed as well. Double-sided formats used either "sector/head/track" or "sector/track/head". I'm not aware of any "head/sector/track" formats or other combinations. Typically, each parameter was counted up from low to high, indicated by "+", (with sectors normally starting at 1, sometimes at 0, and heads and tracks normally starting at 0) or sometimes also counted down, indicated by "-".

There also was some skew (specified either physically as angle or logically as offset in sector numbering) to be taken into account when switching the head, or when moving from one track to another. The latter was called track-to-track skew or track sector skew, the former might have been called head-to-head skew or head sector skew, or there might have been another extra term for it (I would have to look this up to be sure). --Matthiaspaul (talk) 18:21, 19 June 2013 (UTC)

Track interleaving as was written in this article had nothing to do with sector mapping or skewing. BTW, as best I recall, single sided and double sided FDDs used the same logical to physical sector mapping, namely sector physical location given by CHS - Cylinder/Head/Sector, with the single sided having Head=0 only. I suppose one could argue that sector interleaving was a form of mapping but that is not Track interleaving whatever that is.

Sector skewing was used by in some clever designs to maximize sequential transfer rate by skewing the sector location between tracks (both head switch skew and track change skew) so as to avoid missing revolutions. Again this is not Track interleaving Tom94022 (talk) 22:07, 19 June 2013 (UTC)

Instructions are interleaved too

See IBM 650, APEXC (where the BTM1200 is mentioned).99.65.176.161 (talk) 20:58, 26 December 2013 (UTC)

The IBM 650 was a von Neumann architecture machine, so instructions are data, and the reference to "dynamic modification of opcodes" in the APEXC page suggests it was also a von Neumann architecture machine. Guy Harris (talk) 22:48, 26 December 2013 (UTC)

The 650 literature used the term optimization for interleaving instruction words with just enough of an interleave to allow retrieving the next instruction without losing a revolution, hence the name Symbolic Optimal Assembly Program (SOAP). Informally, use of a constant interval was called sloptimization. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 15:34, 6 February 2022 (UTC)