MFM
- Modified Frequency Modulation
The first IBM XT computers used MFM hard drives. MFM allows a transfer rate up to 5MB/s and were only available in sizes from 5MB to 100MB. The data cable was 20 pin and another 34 pin cable. These drives fit into a 5.25” bay. It was not uncommon to have as many as 10 or more bad sectors with the drive still fully functional despite the areas that were marked. The drives had to be parked before the PC was transported to prevent damage from the drive heads impacting the disks.
NRZ
RLL
- Run Length Limited
The successor to the MFM drive, externally appearing the same as an MFM drive. This encoding method can store 50% more data on the disk than MFM. The RLL drive connected to the RLL controller with two cables just likes with MFM. The RLL encoding method is still used today although RLL drives are not.
SCSI
- Small Computer System Interface
IDE
- Integrated Drive Electronics
EIDE
- Enhanced Integrated Drive Electronics
ESDI
- Enhanced Small Device Interface