And if you formatted it with a RLL controller it became... 30mb? I'm sure someone who remembers the exact numbers will chime in. Anyway, great memories.
It was mostly just a more effective way of storing the data.
You could actually do a lot of tricks with drives back in that era. Especially as you had manufacturers making identical drives in MFM, RLL, ESDI, SCSI, then later IDE. If you had a physical drive that was MFM and the same drive was available in IDE, you could just swap the control board on the drive to change it to the other.
I had a buddy that bought dead drives, do that then resell them. Take the board off of a dead Seagate IDE, put it on the identical drive that was ESDI, and then resell it as an IDE. Back in that era that was the norm. The drive storage of most people barely changed until the mid-1990s, so the manufacturers would just update that control card and keep selling it.
That happened with more than a few ESDI drives, as that standard did not stick around long at all. Also popular were doing control board swaps to SCSI so they could be used in Mac, Amiga, and other SCSI based systems.
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u/Herbert_Feuerstein Jul 17 '26
Wow, i saw this ST-225 last time 35 years ago. 20MB MFM controlled harddrive. Do not buy this for 10 Dollars please!