ST506 disk interface
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.
The ST506 interface has two two ribbon signal cables, one 34-pin control cable and one 20-pin data cable.
The control cable is shared by up to four disks whereas each disk has got its own dedicated data cable. A lot of 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
The ST506 data rate is 5 Mbits/sec, and the code to store data on the magnetic media is MFM.
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.
Later RLL technology increased storage capacity by 50% by squeezing 26 instead of 17 sectors into a track.
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.
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.
