Seagate introduced the ST-506, the first 5.25-inch HDD, with a capacity of 5 megabytes in 1980 for the personal computer.
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 110MB. 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.
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
SCSI busses support up to seven additional devices attached at one time, an eight counting the adapter itself. The SCSI bus structure has two ends, with devices connected between them. On each end of the SCSI bus, you must install a terminator pack to help reduce the amount of noise on the bus cable. Therefore, a SCSI bus has two terminators, one on each end.
- Fibre Channel Protocol (FCP) is the interface protocol of SCSI on the Fibre Channel.
IDE
- Integrated Drive Electronics
EIDE
- Enhanced Integrated Drive Electronics
IDE with the ATA-2 extension which provides three enhancements to traditional IDE. Data transfer is faster, maximum drive capacity is higher, more drives per channel.
The inclusion of ATAPI, AT Attachment Packet Interface, which defines device characteristics for IDE devices like CDROM drives by converting the SCSI command set to an IDE interface command set.
ESDI
- Enhanced Small Device Interface
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SATA
- Serial Advanced Technology Attachment
Communicates at a rate of 1.5Gbit/s. It can only handle a single pending transaction at a time while SCSI disks can handle multiple outstanding requests, allowing the drive targets to re-order the requests to optimize response-time.
SATA 2
- Serial Advanced Technology Attachment Two
Communicates at a rate of 3Gbit/s. The term SATA II has grown in popularity as the moniker for the SATA 3Gb/s data transfer rate even though it is a misnomer. SATA II was the name of the organization formed to author the SATA specifications, now known as the Serial ATA International Organization, or SATA-IO. 3Gb/s has become synonymous with the term SATA II.