IBM's mini computerslack thereof 831

PCs are getting there.

The original interface for a hard disk was the ST506 interface, never properly standardized; just happened to be reasonably well documented by IBM.

This interface has a ribbon "bus" cable shared between controllers and disk, and "data" cables going directly from controller to disk. It looks like a bowldereized ESMD system, still in need of the occational sacrifice of a small goat to work properly.

Then the engineers revolted, and built SCSI. It took a few generations, but then SCSI became a decent bus with a packet protocol on it. The bus part of it is designed "right" electrically, and that drives cost up. It remains the system of choice where reliability counts.

Enter IDE-ATA. It uses an electrically simple interface, designed for a single disk, with a second "slave" kludged on. It does run a protocol very similar to SCSI on top of this though. It has gone through a dozen or more incremental upgrades, changing names underway. They are pretty good in downward compatability, the number of changes considered. I wouldn't push it though.

Then the electrical interfaces were changed, and ATA went where SCSI should have gone and invented a serial link, dedicated from disk to controller. This brings it all where BAH wants it; to a comms protocol between intelligent devices. A SATA raid controller is electrically simple, and is really only a hybrid multiplexer. It is all SCSI commands and packages on top of a point to point layer.

SCSI is following suit, and is adapting to similar technologies, as well as a fiber optic interface. All as comms protocols.

It is getting there. The comms is just handled inside the kernel driver.

-- mrr