Path: utzoo!utgpu!watmath!uunet!lll-winken!pacbell!att!mtunb!jcm
From: jcm@mtunb.ATT.COM (was-John McMillan)
Newsgroups: unix-pc.general
Subject: Re: Multiple combo cards in 7300?
Summary: Yes, Yes?, No!, Yes, ?, too late
Message-ID: <1343@mtunb.ATT.COM>
Date: 21 Dec 88 18:59:49 GMT
References: <166@orac.pgh.pa.us>
Reply-To: jcm@mtunb.UUCP (was-John McMillan)
Organization: AT&T ISL Middletown NJ USA
Lines: 54
Dis-Organization: Everywhere
Bcc: jcm


	> Is it possible to put more than one combo card in a 7300?
Yes.  It's frequently done.
	> If so, can they both have memory on them
Yes.  But not for any good reason :-)  [A 1.0M and .5M card might work.]
	> (for instance, one 1.5M combo card, and one 0.5M card)?
No.  [See below.]
	> Can you use more than one combo card if only one has memory?
Yes.  It's frequently done.
	> I should probably know all this stuff from the docs...
(I would hope they're of some use...)
	> Unfortunately, I got my card without any documentation...
And, you tuned into the news columns a week too late.

To reprise:
	There are 2 (logical) banks of RAM on the card:
		- a .5 MB bank
		- a 1 MB bank (containing 2 physical banks of RAM)
			...A 1.5 MB card uses BOTH logical banks.

	Each bank is at a FIXED address (and is assigned fixed physical
		banks on the card).
			...Ergo, you CANNOT use 1.5 MB on one card and
			.5 MB on another -- the .5MB component of each
			would occupy the same address space.
			...Ergo, when one migrates from .5 to 1 MB, you
			must de-populate the one physical bank, only to
			re-insert the chips in an adjacent bank.

There is a 2 MB RAM card available: it is the only trivial solution I've
seen to getting 2 MB expansion-bus memory.  (The past two weeks of news
items have discussed clever, masochistic modifications to get 2 MB ;^}  )

Do you need 2 MB on the expansion bus?
	I've used 7300/3B1's intensely for 3.8 years, compiling,
	StarLAN'ing, and providing troff/PostScript(R) services.
	I wouldn't expect noticeable improvements migrating from
	3.5 to 4 MB (total), and wouldn't expect much in migrating
	from 2.5 MB to 3 MB.
Yes Virginia, there are exceptions.

Disks are typically the principle factor in sustaining high throughput.
RAM serves to either diminish paging activity or increase disk-cache
"hits".  For the 3B1, a cache limit of around 120 is absolute because
of the design-constrained 1.5 MB limit on kernel virtual address space
-- more specifically, the .5 MB limit on core-kernel + tunable arrays.

Below 2 MB RAM (total) things deteriorate, and below 1.5 MB one can
plummet into page thrashing with large codes.  (Try large compilations
with .5 RAM for fun :v)

If you're having problems with throughput, maybe a disk upgrade will be
in your generic seasonal stocking.  Seasoned greetings, and all that.
				- - - - - -
John McMillan	-- att!mtunb!jcm	... speaking only for himself, if that.