Difference between revisions of "ST506 disk interface"

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The '''ST506''' disk interface (other common names: ST-506, ST412, ST-412, or sometimes even the misleading MFM) was introduced in 1980 with the Seagate 5MB disk of the same name. The way to success was paved by the follow-up 10MB ST-412 disk model that was used by IBM for the IBM Personal Computer XT Model 5160. Soon many other hard disk manufacturers followed suit with their own models and thus helped the ST512 interface to be successful.
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The '''ST506 disk interface''' (other common names: '''ST412''', '''ST506/ST412''', or often the misleading '''MFM disk''') was introduced in 1980 by [[Seagate]] with the 5MB [[hard disk]] of the same name. It quickly became a ''de facto'' [[interface]] standard in the industry, although it was never formalized, or even given a formal name (hence the plethora of names for it used by people).
  
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The ST506 interface has two two ribbon signal cables, one 34-pin control cable and one 20-pin data cable.
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It provides the [[analog]] signal from the [[head]], not a [[digital]] bit stream (as later disk interface standards did). Most early [[device controller]]s used [[Modified Frequency Modulation|MFM]] [[encoding]] (hence the name, but that is misleading, for several reasons) on that to produce a bit stream, at a data rate of 5 Mbits/sec. Towards the end of its lifetime, [[run-length limited coding|RLL]] encoding was used instead.
  
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The control cable is shared by up to four disks whereas each disk has got its own dedicated data cable.
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(In addition to the replacement of MFM by RLL, 'MFM disk' is misleading as a name for this interface standard since MFM was widely used by other [[magnetic storage]] devices at the time; see [[Special:WhatLinksHere/Modified_Frequency_Modulation|here]] for some.)
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A lot of PC ST506 controllers support only two disk drives.
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The use of RLL increased storage capacity by 50%, by squeezing 26 sectors into a track instead of 17. Because of the identical hardware interface, RLL hard disks can be easily reformatted to use MFM, with suitable controllers. On the other hand, the opposite direction is not recommended, since the higher sector density of RLL in MFM disks leads to serious problems with the reliability of data storage.
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The way to success was paved by the follow-up 10MB ST412 disk model, which was used by [[International Business Machines|IBM]] for the [[IBM Personal Computer]] [[IBM XT|XT Model 5160]]. Soon many other hard disk manufacturers followed suit with their own models, and thereby helped the ST506 interface to become very successful. The largest ST506 hard drive believed to have ever been made is the MAXTOR 2190, which gains about 159 MB from 1224 cylinders, 15 heads, and 17 512-byte sectors per track.
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==Details==
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The ST506 interface uses two [[flat cable]]s, one a 34-pin control cable, and the other a 20-pin data cable. The control cable is shared by up to four disks whereas each disk has got its own dedicated data cable. (Many PC ST506 controllers support only two disk drives.)
  
 
The data cables transmit the read and write signals, the control cable carries the control data such as:
 
The data cables transmit the read and write signals, the control cable carries the control data such as:
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* Ready
 
* Ready
 
* Track 0
 
* Track 0
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* Write Gate
 
* Write Gate
  
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The ST506 data rate is 5 Mbits/sec, and the code to store data on the magnetic media is [[MFM]].
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==External links==
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The largest ST506 hard drive believed to have ever been made is the MAXTOR 2190, which gains about 159 MB from 1224 cylinders, 15 heads, and 17 512-byte sectors per track.
 
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Later [[RLL]] technology increased storage capacity by 50% by squeezing 26 instead of 17 sectors into a track.
 
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The largest ST506 hard drive believed to have ever been made is the MAXTOR 2190, which gains about 159 MB from 1224 cylinders, 15 heads, and 17 512-byte sectors per track.
 
  
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Because of the identical hardware interface, RLL hard disks can be easily reformatted to MFM with suitable controllers. On the other hand, the opposite way is not recommended, since the higher sector density of RLL in MFM disks leads to serious problems with the reliability of data storage.
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* [https://en.wikipedia.org/wiki/ST506/ST412 ST506/ST412] - includes a good history of how it came to be a 'de facto' standard
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* [https://www.redhill.net.au/d/1.php hard drive history - beginings: mfm drives of the 1980s] - a good brief intro
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* [http://www.pdp8online.com/mfm/mfm.shtml MFM Hard Disk Reader/Emulator] - still supported
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** [http://www.pdp8online.com/mfm/mfm_old.shtml MFM Hard Disk Reader/Emulator] - the early stages of that project
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* [http://www.bitsavers.org/pdf/seagate/mfm/ST-506/ST506_Product_Manual_Jul83.pdf ST506 Product Manual]
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* [http://www.bitsavers.org/pdf/seagate/mfm/ST-412/ST406_ST412_ST419_Product_Manual_Jan84.pdf ST412 Product Manual]
  
 
[[Category: Mass Storage]]
 
[[Category: Mass Storage]]
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[[Category: Interface Standards]]

Latest revision as of 17:20, 2 December 2023

The ST506 disk interface (other common names: ST412, ST506/ST412, or often the misleading MFM disk) was introduced in 1980 by Seagate with the 5MB hard disk of the same name. It quickly became a de facto interface standard in the industry, although it was never formalized, or even given a formal name (hence the plethora of names for it used by people).

It provides the analog signal from the head, not a digital bit stream (as later disk interface standards did). Most early device controllers used MFM encoding (hence the name, but that is misleading, for several reasons) on that to produce a bit stream, at a data rate of 5 Mbits/sec. Towards the end of its lifetime, RLL encoding was used instead.

(In addition to the replacement of MFM by RLL, 'MFM disk' is misleading as a name for this interface standard since MFM was widely used by other magnetic storage devices at the time; see here for some.)

The use of RLL increased storage capacity by 50%, by squeezing 26 sectors into a track instead of 17. Because of the identical hardware interface, RLL hard disks can be easily reformatted to use MFM, with suitable controllers. On the other hand, the opposite direction is not recommended, since the higher sector density of RLL in MFM disks leads to serious problems with the reliability of data storage.

The way to success was paved by the follow-up 10MB ST412 disk model, which was used by IBM for the IBM Personal Computer XT Model 5160. Soon many other hard disk manufacturers followed suit with their own models, and thereby helped the ST506 interface to become very successful. The largest ST506 hard drive believed to have ever been made is the MAXTOR 2190, which gains about 159 MB from 1224 cylinders, 15 heads, and 17 512-byte sectors per track.

Details

The ST506 interface uses two flat cables, one a 34-pin control cable, and the other a 20-pin data cable. The control cable is shared by up to four disks whereas each disk has got its own dedicated data cable. (Many PC ST506 controllers support only two disk drives.)

The data cables transmit the read and write signals, the control cable carries the control data such as:

  • Ready
  • Track 0
  • Direction
  • Step
  • Index
  • Seek Complete
  • Head Select
  • Drive Select
  • Write Gate

External links

Retrieved from "https://gunkies.org/w/index.php?title=ST506_disk_interface&oldid=32008"