From: wlsmith@valve.heart.rri.uwo.ca (Wayne Smith)
Subject: Re: Bus def's ==> Re: EISA vs. ISA (& VESA, VL-bus, Local bus)
Organization: The John P. Robarts Research Institute, London, Ontario
Date: Sat, 12 Dec 1992 02:41:44 GMT

In article <8738@lhdsy1.lahabra.chevron.com> hwrvo@kato.lahabra.chevron.com (W.R. Volz) writes:
>|> >|> 	* ISA         (the mormal 386 type bus, right?)
                              ISA is based on the original IBM PC 8-bit bus,
                              but now commonly refers to the IBM PC-AT bus,
                              which extends the PC bus to 16 bits, doubles the
                              number of interupts and DMA channels, provides
                              for at least 16 Mb of ram, although many 386
                              motherboards do not have bus-mapped ram.
The PC-AT bus was rated as more than adequate 2 years ago when comparing
EISA and microchannel 386's and single user usage.  I still think that
analysis is correct.  If you need Local bus or eisa, than you need a
small unix machine, or you should stop playing games or stop using your
computer to play real time video or audio (that's what your home stereo
and tv/vcr are for)...    :)

>|> >|> 	* EISA        (extended ISA, 32 bit, look like IAS but twice

There "once" was a group of nine (Compaq, uh, who else?) that came up with
EISA as the answer to IBM's microchannel.  IBM figured it had to come up
with a proprietary bus (to get the pc market back), and the Group of Nine
thought they had to come up with their own "public domain" bus that equalled
the performance (bus-mastering) of IBM's microchannel.

IBM's microchannel never caught on (it was expensive, add on cards were
expensive, and the performance for single-person applications just wasn't
there.  EISA is suffering a similar fate, although if you want to get
technical, an EISA bus does match the performance of the 486 better than
the PC-AT ISA bus, but that's like saying the Chrysler HEMI 426 should
have had the body and handling of a Ferrari.

>|> >|>                        longer right?)

The EISA bus, unlike IBM's microchannel, is configured in such a way
that regular ISA cards can be plugged into them.  This gives you the
best of both worlds, that is the ability to use currently available
(and cheap) ISA cards, an upgrading to EISA cards when they become
available, or cheaper.

>|> >|> 	* VL-bus      (differnt type of expansion slot, looks all
>|> >|>                        diferent, much smaller than ISA, connected to the
>|> >|>                        CPU directly, good for video cards, or is it VESA?)
>|> >|> 	* Local Bus   (?)
>|> >|> 	* VESA        (?^10)
>|> 
>|> >EISA is a new Extended ISA bus. It is 32 bits wide and runs at 33 mhz, 
>|> >I think. This bus should be 32 * 33 / ( 16 * 8) or about 8 times faster
>|> >than the ISA bus. I don't know what cards are available but ISA is 
>|> >compatible with this bus though is halves the bus speed. Don't know what
>|> >that does to cards expecting an 8 Mhz bus.
>|> 
>|> People keep asking this question, and people keep getting it wrong.
>|> EISA runs at ***8.33*** MHz.  It will transfer at FOUR times the speed
>|> 
>
>I found that I can learn much more by answering a question, even if
>I know the answer is wrong. I know that someone will correct me and I
>can take the median of the answers and the true answer. Try calling
>several vendors and ask them the same question and see if you get the

The traffic in this group is WAY WAY too high, and should have been 
split up long ago.

I have also heard that IESA runs at 8.33 mhz.  This is *probably* a
bad thing if you can't change it.  Some 286's, and most 386/486's
allow you to crank the bus speed right up to the processor speed.  
This means that with ISA cards, you can crank the bus up to the point
where the computer still functions adequately (on my 286-25, I have
a fax modem, an ET4000 video card, and a Maxtor 213 Mb drive, and
they don't mind the 12.5 mhz bus speed).

(side point: Maxtor 123 Mb ide drives don't like 12.5 mhz bus speed.)

And for VESA.
VESA is a video STANDARD, it's the industry's attempt to standardize
Super VGA, because IBM's vga standard stops at 640x480x16 (although
there is the 8514 standard, but it's not a good spec).

Anyways, a VESA compatible video card is supposed to adhear to rules
that allow application software control the video card in 800x600
ans 1024x768 modes.  In other words, *I think*, an application program
can *ask* a video card what it can do (resolution wise) and tell the
video card to go into any video mode in a standard way, withoug the
need for drivers.  But I stand corrected...

-Later:Wayne-
Newsgroups: comp.sys.ibm.pc.hardware,comp.sys.ibm.pc.misc