question about EISA/VLB and EISA/ISA/VLB MBs

question about EISA/VLB and EISA/ISA/VLB MBs

Post by Jeffrey Wiegl » Sat, 01 Jan 1994 12:00:03

I'm currently in the process of upgrading my 386/40 machine to a 486DX2/66
machine and I need to buy a motherboard.  I have to have VL BUS since I
have a #9 VL BUS card coming. other than that I also wanted an EISA bus.
I'm finding it rather confusing and difficult to find true EISA/VESA
motherboards. most of what I find are "hybrid" boards that also have ISA
slots such as 3EISA/2ISA/2VL or such thing. and these tend to be
substantially less money than the true EISA/VL boards.

what I would like to know is what performance differences I'll see between
a true EISA board and one of these hybrid boards.  is the extra money for
the true EISA/VL board worth it?  will I run into difficulties or
incompatibiities with the hybrid boards that I wouldn't if I went with a
true EISA/VL board.  the reason I'm asking is that I'm thinking of breaking
down and buying one of the hybrid boards.

also some boards use 72 pin simms and some use 30 pin simms.  the 30 pin
simms are cheaper but again... is it worth the extra money to get 72 pin
simms and the motherboard that supports them?

please help clue me in on anything I don't know or may not have thought of.

oh it might also help to know that I plan on using the board to run the
Linux operating system if that makes a difference.

thanks for your time and advice I really appreciate it.

- Jeff


1. EISA or VLB (EISA th

Hmmm, amazing, almost everything stated there was incorrect!

The closest thing to a "multitasking bus" you'll find is one using split
transactions.  No common PC bus does split transactions: PCI can do
disconnects for slow devices, but that's not quite the same thing.

PCI is well specified electrically.  Most problems have been BIOS setup
problems, which have been resolved far more quickly than the early EISA

The ISA bus is compatible with the poorly designed original PC bus, but
cards designed for ISA bus (as opposed to the PC or XT) are robust and
reliable if there are no conflicts.  It's a fine bus for low-bandwidth
devices, and what other bus has 2IDE/2F/2S/1P/1G I/O cards for $15?

The ISA bus has only 24 address lines, but that doesn't preclude having
more than 16M in the machine.  Nor does having >16M mean that you can't use
shared memory adaptors.

The ISA bus can support busmasters, and even multiple busmasters.  The
processors in Beowulf (a 16 processor Linux cluster) have a VLB busmaster
ethercard and one or two ISA busmaster ethercards.  The only major issue is
that ISA SCSI busmasters are usually set to use most of the bus bandwidth
and must be reconfigured to share.

The fastest SCSI cards are probably not EISA, but PCI based.  To say that
PCI burst mode at 133.3MB/sec is not faster than EISA is just pure bunk.

Amazingly (hey, I never would have predicted it) many PCI cards are about
the same price as their VLB counterparts, and far less expensive than
EISA cards.


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