
Seagate ST506 (The First 5.25“ Hard Disk Drive) - peter_d_sherman
https://en.wikipedia.org/wiki/ST506/ST412
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peter_d_sherman
Excerpt:

"The ST506 HDD was the first 5.25 inch hard disk drive, introduced in 1980[2]
by Shugart Technology (now Seagate Technology). It stored up to _5 megabytes_
after formatting and cost US$1,500 (equivalent to $4,561 in 2018).[3] The
similar, 10-megabyte ST412 HDD was introduced in late 1981. The ST225 was
introduced shortly thereafter with 20 megabytes and half the height. All three
used MFM encoding, a widely used coding scheme. A subsequent extension of the
ST412 interface, the ST412HP interface, used RLL encoding for a 50% increase
in capacity and bit rate.

The ST506 drive connected to a computer system through a disk controller. The
ST506 interface between the controller and drive was derived from the Shugart
Associates SA1000 interface,[4] which was in turn based upon the floppy disk
drive interface,[5] thereby making disk controller design relatively easy.[2]

The ST412 interface was adopted by numerous HDD manufacturers such that the
interface became a de facto industry standard for disk drives[6] well into the
1990s."

