From: davidsen@ariel.crd.GE.COM (william E Davidsen)
Newsgroups: comp.periphs.scsi,comp.sys.intel
Subject: Re: EISA vs. ISA - which is better?
Date: 11 Sep 92 13:59:00 GMT
Reply-To: davidsen@crd.ge.com (bill davidsen)
Organization: GE Corporate R&D Center, Schenectady NY

In article <BuDB4r.Lx5@unx.sas.com>, sasbge@ant.unx.sas.com (Gantt Edmiston) writes:
| 
| I'm buying my first PC and I'm completely ignorant and/or baffled
| as to which path to take as it relates to EISA or ISA bus systems.
| 
| One thing to consider is that I currently own two Maxtor 280MB SCSI
| hard disk drives.  An EISA system would allow me to utilize them.
| An ISA system would require me to purchase an additional SCSI controller.

  Are you somehow assuming that EISA = SCSI or something? There's no
relationship. If you buy a system which has SCSI, you paid for it. And
the EISA SCSI controllers are a lot more than the ISA versions.

| EISA system appear to be about $1000 more than the equivalent ISA
| machine.  More like $700 more if I consider the fact that the SCSI
| controller already comes with the EISA option.

  You're looking at one vendor and generalizing. And the controller
which comes with may not be the one you want, anyway. I strongly
recommend Adaptek or Bustek, or some other Adaptek compatible, not
because it's the best (although I could argue that), but because
whatever you want to run now of in the future supports it, whether that
mean DOS or UNIX or OS/2 or Linux, or whatever.

  Now another sad fact, for a single user system you will find EISA not
cost effective. The main gain is bandwidth, and on a single user system
you have memory (not on the bus), video (ISA+local bus is cheaper and
faster), and disk. And the limiting factor with disk is how fast the
data comes off/on the the platters, not the bus. So no matter how fast
the bus, any given disk transfer won't be a bit faster.

  The gain comes in an o/s which overlaps execution and i/o, like UNIX.
Then the EISA system will deliver as much a 3% more CPU. That's about
the difference between a ISA and EISA controller, assuming that both are
set up as bus master and are stealing cycles from the CPU. Under DOS the
CPU waits, so all that savings goes into the idle loop, which runs
faster.

  EISA is a small but useful win when you have multiple controllers, and
to some extent with one controller running multiple devices, however, it
only helps with non-DOS operating systems.

  Another factor is the convenience factor of EISA. Every time you
change an EISA board you have to run EISA config to tell the bus about
the characteristics of the card in that slot. If you don't plan to
change things that's a tiny issue, but if you try new stuff frequently
it becomes a major hassle, particularly for those of us who don't run
DOS and have to buy a copy of DOS to boot only to run the config.

| In case it's not obvious, let's assume that I don't know one system
| from the other =-).  What considerations and facts do I need to know in
| order to make an informed choice between EISA or ISA?  I don't consider
| the $$$$ to be the number one factor in the decision.  It does matter,
| it's just not the most important thing.  I want to buy a system that will
| hold it's value (to me and possibly to others in the future).

  EISA is a reasonable thing to use on servers, either file or compute,
including any multiuser system. After looking at the performance gains I
decided that it didn't make sense for me to put money into that, vs
other features like a tape drive to back up large disks, better video,
etc.

  For a single user system the gain from EISA is "measureable but not
perceptable." An EISA system will not *feel* faster than ISA under
single user loads, and that's the major reason I don't feel they're cost
effective.

  You can get a SCSI ISA card for $200-250, a 2S+P card for about
$15-20, and that replaces the cheap IDE controller which comes with most
ISA machines. That leaves some money for other features in the same
budget which would support EISA.

  You should weigh the advantages for your particular case and then
decide if EISA is the way to go. It will not raise the resale value by
as much as you pay, but it could allow you to run some nifty peripheral
five years from now if you don't replace the motherboard before then. I
find that I am replacing my m/b about every two years, while the old one
still has some resale value or use elsewhere. I do it every time I can
double my performance for $600 or less.

-- 
bill davidsen, GE Corp. R&D Center; Box 8; Schenectady NY 12345
    I admit that when I was in school I wrote COBOL. But I didn't compile.
Newsgroups: comp.periphs.scsi