Re: Please Advise: SCSI vs. IDE (fwd)

Linus Torvalds (
Sun, 29 Sep 1996 13:29:31 +0200 (EET)

On Sat, 28 Sep 1996, Steven N. Hirsch wrote:
> > This is a tough issue. It really it really depends on several things.
> > 1) If your controller is a busmastering SCSI controller - I believe that
> > the 1542 is not (but I might be wrong)
> You are. It is.

Well, the aha1542 is busmastering the same way a Trabant is a car.

The aha1542 is _ISA_ busmastering, which means that if you have the choice
between a reasonable modern PIO device and a aha1542, the PIO device is
likely to be much faster. Especially as most people tend to have more than
16MB in their machines these days..

With ISA busmasters, the kernel has to double-buffer the IO memory for the
16MB+ area, which makes the whole idea with DMA fail completely. The extra
copy is _worse_ than the CPU doing the reading by hand in the first place.

My personal opinion: get IDE if it's a single-user machine and you don't have
any special requirements like SCSI tapes or scanners anyway. It's likely to
be faster than any but the high-end SCSI setups, and it's cheaper and easier
to find. And despite SCSI proponents saying that SCSI is so trouble-free, I
get a lot more trouble-reports about SCSI cabling problems than I get about
IDE cabling.

If you're going to set up a multi-user machine and/or a web server, get a
high-end PCI SCSI card. In no case get something like a aha1542 these days
(they were fine 5 years ago, and I still have one, but they really aren't
worth it any more).

Oh, the ncr SCSI chipset is cheap, and works for a lot of people, but it's
also the chipset I get the most complaints about. There is something wrong in
NCR land (and I'm not necessarily blaming the hardware, it might be a driver
problem or a combination of hardware+driver - you might have to try one or
the other of the two drivers that are available for it).

Personally, if I bought a SCSI card, I'd buy one of the supported PCI
BusLogic cards.