● What is commonly referred to as an ‘MFM’ drive, is really a drive that uses the ST506/ST412 interface.
● Originally, only 4 heads were supported, because the third head-select bit (bit 2) was not used; it was marked as RESERVED.
● The ‘Reduced Write Current’ signal later becomes the fourth head select bit (allowing for up to 16 heads).
Control connector
[ READY ]
Determination of
READY
[ WRITE FAULT ]
Detection of certain
problems
[ INDEX PULSE ]
Index Sensor
[ TRACK 0 ]
Track 0 Sensor
[ STEP DIRECTION ]
[ STEP PULSE ]
Stepper
Control / Driver
Stepper
Motor
[ SEEK COMPLETE ]
[ DRIVE SELECT 1 ]
[ DRIVE SELECT 2 ]
[ DRIVE SELECT 3 ]
Drive
Select
Enable circuitry
[ DRIVE SELECT 4 ]
[ HEAD SELECT - BIT 0 ]
[ HEAD SELECT - BIT 1 ]
[ HEAD SELECT - BIT 2 ]
[ REDUCED WRITE CURRENT ]
[ WRITE GATE ]
RW Head 0
Write
Circuitry
[ WRITE DATA + ]
[ READ DATA + ]
[ READ DATA - ]
[ DRIVE SELECTED ]
RW Head 1
Head
Select
Circuitry
RW Head 2
RW Head 3
RW Head 4
RW Head 5
RW Head 6
[ WRITE DATA - ]
Data connector
Controller
● ‘Drive Selected’ signal only generated by some drives (e.g. Maxtor XT-1000/2000 series).
RW Head 7
Read
Circuitry