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What was the head/track/sector layout of the ST506? Rpresser 15:06, 20 June 2007 (UTC)

153 tracks per surface
4 surfaces (heads) per drive
10,416 bytes per track unformatted
typically formatted with 32 sectors per track and 256 bytes per sector.
The ST506 was a "dumb" interface so the user capacity depended upon the controller to which it was attached. The above comes from the ST506 Service Manual[1], May 1982Tom94022 21:10, 20 June 2007 (UTC)


  1. ^

Seagate or Shugart?[edit]

The ST506 and ST412 manuals that I have looked at (through bitsavers) indicate that the drives were Seagate.

It looks to me that Shugart drives were numbered with SA, and Seagate with ST, further evidence for Seagate.

I don't know when the change was made, though.

Gah4 (talk) 21:27, 17 January 2008 (UTC)

Shugart Associates [f. 1973], later Shugart Corporation is a different company than Seagate Technology originally Shugart Technology [f. 1979]. Alan Shugart was a founder of both. Tom94022 (talk) 17:00, 18 January 2008 (UTC)

Yes, but which company is responsible for the ST506 and ST412?

Gah4 (talk) 04:28, 14 February 2008 (UTC)

Seagate Technology Tom94022 (talk) 06:08, 14 February 2008 (UTC)


Out of curiosity, how much did one of these cost in 1980? I imagine they weren't available to the public, and so researching the cost would be hard, but perhaps someone reading this was actually there, in 1980, and can provide a source. -Ashley Pomeroy (talk) 23:21, 1 January 2011 (UTC)

The Seagate Sept 24, 1981 Prospectus gives the FY1981 revenue of $9.9 million for approximately 13,000 drives or an ASP of about $750. The claim then was that this was the first HDD priced below $1000 which probably was true although the Shugart SA1000 or the Memorex 101 may have beaten it below that threshold. Tom94022 (talk) 00:07, 2 January 2011 (UTC)

As well as I remember, for some years the usual high end microcomputer drive to buy was about $1000. The capacity increased over the years, but the price stayed about the same. The price of older drives would fall as new ones were introduced. Minicomputer drives, such as SMD, were more expensive. Gah4 (talk) 20:54, 28 April 2016 (UTC)

Interface limitations[edit]

The interface is limited in number of heads because the 4-bit head addressing can only express 16 combinations. The drive selection scheme is one wire per drive, so only 4 drives. And controllers only expect 5 Mbit/s per documentation. Bytesock (talk) 13:08, 28 April 2016 (UTC)

Limitations vs specifications[edit]

The paragraph was reverted because it ascribed as a "limitation" a mixture of some specifications and some unsupported limitations. The ST506 interface is indeed limited by the 4 drives select and 3 or 4 head select lines. If used according to the Seagate specification it can address either 8 or 16 heads, but one can use unused drive select lines as head bits going beyond 16 so the limitation is not 16. I know of know published 6.1 meter cable length limitation and it is not supported by the citation. The data rate is clearly not limited to 5 Mbits/sec since it is capable of 7.5 Mbits/sec when used in RLL and most likely even more since the original 5 MHz wasn't picked from any transmission limitation. Acurately written the sentence would be OR and since it didn't add a lot to the article, I reverted. Tom94022 (talk) 21:12, 28 April 2016 (UTC)

The specification does indeed limit what you can do with any interface. Of course, the interface can be changed circumventing the limitation, but then it would no longer be a ST-506 interface which is what the article is about. You clearly did not read the specification cited because the maximum cable length is specified as 20 feet (which is 6.096 metres - but 6.1 metres is close enough). A relatively simple calculation gives the theoretical maximum length as 6.9 metres so 0.8 metres is a reasonable safety margin. --Elektrik Fanne 16:28, 26 July 2016 (UTC)