Re: ULTRA ATA/100 announced

From: Matthias Andree (
Date: Wed Jun 07 2000 - 05:22:58 EST

"Dr. Kelsey Hudson" <> writes:

> I heard somewhere (although Andre would probably know for sure) that even
> though ATA is deemed 'busmastering,' meaning you can access (command) both
> drives at the same time, you can still only recieve data from one drive at
> a time.


> Hence the reason SCSI is better, being that you can access and recieve
> output from every drive on the chain at the same time.

Wrong. SCSI has only one data bus, just like ATA has just one data
interface. Still, SCSI USUALLY implements dis/reconnect, which usually
does not work within the same ATA channel, but usually works if you go
with one drive per ATA channel (obviously limiting your machine to two

> I also heard somewhere that SCSI releases CPU strain, because a lot of
> the I/O is done on the card and not by the CPU. But then again this
> could be a controller-specific issue too...

It surely is. There are SCSI controller chips that have script engines
and handle the entire protocol "in silicon" (such as SYM53C8xx, aic7xxx
AFAICS) and there are chips that don't (probably the older chips).

> SCSI also has the flexibility of external devices, which to my knowledge
> ATA still has yet to support (except in paralell port versions, which are
> slow).

Parallel port devices are no ATA devices. Some of them use
parallel-to-SCSI convertors (such as some Olympus Power-MO).

Matthias Andree

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