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

Steven N. Hirsch (
Sun, 29 Sep 1996 18:48:26 -0400

Linus Torvalds wrote:
> 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.

Greetings, oh kernel-meister!

> 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..

Actually, with a modern SCSI drive it gives even the quickest IDE drives
a good run for their money (on an ISA-only machine). Don't get me
wrong, I'm not suggesting that anyone run out and buy one - this thread
has gotten _real_ jumbled, and I was only correcting the person that
didn't think the 1542 was a bussmaster..

> 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.

Yes, absolutely true. OS/2, Win/DOS and the rest also switch modes with
large amounts of memory installed. Not to mention that a lot of older
ISA buss machines didn't cache memory above the 16-meg line either..

> 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.

I suppose YMMV. I have experienced mucho grief of all sorts with IDE
drives, and have never seen problem number one with SCSI cabling..
Variety of experience is the spice of life!

> 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).

Agreed. I have two EISA 486 boxes with 2742 Adaptecs and a new 6x86
unit with embedded AIC7880 (~2940UW). You are preaching to the choir on
this point <g>.

> 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.

Per my posting response to Leonard, I totally concur that the BusLogic
controllers are the best. Now, all they need to do is strike an OEM
deal to get them situated as an on-board controller with someone's P5/P6