What existed before ATA drives?

Answer 1

Before IDE/ATA drives, there were about 4-5 other types of drives.

For PC XT/AT computers, the first used were MFM or "modified frequency modulation." They required a separate controller card, a power cable, a control cable, and a data cable. The controller could operate up to two drives. Common sizes were 10 and 20 megabytes.

Then there were RLL (Run Length Limited) drives . RLL was very similar to MFM and used all the same signals and connections as MFM drives. In fact, most MFM drives could be used with RLL controllers. However, it was stored in a more compressed manner. So the same parameters of drives as MFM could contain 50% more data. So common drive sizes were 15 and 31 megabytes, though there were some larger sizes.

Then there were ESDI (Enhanced Small Disk Interface) and SCSI (Small Computer System Interface) drives. SCSI drives are still used, though most now use a SATA interface, though with a modified command set from SATA, and are known as SAS (SCSI Attached Storage).

Then came the ARLL (Advanced Run Length Limited) format standard. It was similar to RLL, but even tighter, and with Zoned Bit Recording, meaning that more data is placed on the larger cylinders. Before that, data was recorded with the same amount of data on every cylinder regardless of the location on the platter. There were other improvements such as less space used for addressing, integrated drive controllers, and faster speed. They were known as IDE because they had "integrated drive electronics." The interface standard was known as ATA or "Advanced Technology Attachment."

ATA went though a couple of modifications. The ATAPI standard was developed for devices other than hard drives, including CD ROMs, DVD drives, and perhaps even cameras and scanners.

Then there was SATA. That was because Ultra DMA IDE drives could not go past 133 MB/s because of the cabling. To reliably get past 33 MB/s, 80 wires were used, with a ground wire between all of the original 40 wires. That reduced crosstalk. However, that problem would return if they tried to go past 133 MB/s. So they changed to a serial data encoding scheme and clocked it at 10 times the data speed. That enabled 150 MB/s. Now the interface operates at quadruple that speed, giving 600 MB/s.

There is also SAS as mentioned earlier. It is used mostly for servers. It uses a command set similar to SCSI but is electrically compatible with SATA. There is only one-way compatibility in that a SATA drive can be connected to a SAS interface with full compatibility, but a SAS drive cannot work with a SATA controller. Like the latest generation of SATA, the maximum interface speed is 600 MB/s.