Bart Wientjes wrote:
> (E)IDE and ATA were designed and manufactured in order to connect two disks
> to one channel, using one cable. Generally this was regarded as a
> non-desirable configuration, as the standard does not allow for the two
> disks to be addressed simultaneously.
This part I agree with. No parallelism on the same cable.
> Usually one controller has two channels. I think attaching the two disks to
> separate channels of the same controller does allow for paralellism.
> The situation for sata is practically identical, but they skipped the
> two-drives-on-one-channel bit that was a bad option anyhow. And they made
> the cabling more flexible :)
This is the part I was unsure of. I don't think (say 15 years ago) that
there was any parallelism here either. I think the controller could
only handle one drive at a time using cable select and then drive select
on the cable. But with two cables there was the opportunity for
parallelism by enhancing the controller. What I was asking (which
assumed I was correct about how it used to be) was whether current ATA
and SATA controllers do support parallelism.
>
> So if you want to have many disks, you need to have many controllers.
> SCSI of course still is an option. With SCSI you can drive multiple devices
> simultaneously in the same channel (yeah I know it's called a bus), its just
> that you are sharing bandwith.
>
SCSI trivia. SCSI design was based on the early IBM 360 I/O channel design.
Chuck Norcutt
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