Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!asuvax!ncar!mephisto!mcnc!rti!bcw
From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: yo mother
Summary: Info on cards not accurate.
Message-ID: <3403@rti.UUCP>
Date: 11 Jan 90 06:48:28 GMT
References: <20726@kuhub.cc.ukans.edu> <2500@jato.Jpl.Nasa.Gov> <1990Jan5.173839.15620@sj.ate.slb.com>
Organization: Research Triangle Institute, RTP, NC
Lines: 47

In article <1990Jan5.173839.15620@sj.ate.slb.com>, poffen@molehill (Russ Poffenberger) writes:
>
> All these point are good, but nobody has mentioned a VERY CRUCIAL point about
> replacing an XT m.b with an AT style m.b.
> 
> You need to keep in mind what cards are re-useable by the new m.b. Memory cards
> ARE NOT re-useable, you need 16bit memory cards. Some 8 bit disk controllers
> are also not re-useable, even if they are, the performance will make you want
> to get a 16 bit card REAL soon.

This is not quite accurate.  8-bit memory cards will, in general, work just
fine on an AT, but can only be used for memory below 1 MB.  For older AT's,
where there might not be a whole MB on the motherboard, this allows you to
use an older memory card on the AT.  It doesn't help much with most modern
AT-class machines which have a whole MB on the motherboard, because then the
8-bit card can't be mapped onto unused memory (since it can't be mapped onto
the unused memory are above 1MB).   Of course, memory is cheap enough these
days that I can't imagine why anyone would want to save pennies this way --
the performance hit from using 8-bit memory on an AT is substantial, and
why are you buying an AT if you aren't interested in performance!?  Modern
memory is often packaged as SIMMS or SIPS so you might not even be able to
salvage the chips from the old memory card -- and even if the AT uses DIPs
for the memory, they are probably higher density chips than the old PC memory
chips.  But they probably aren't worth too much anyway in modern dollars ...

Ditto for the disk controllers.  Almost all 8-bit disk controllers will work
on the AT, but the performance hit is substantial.  A disk controller just
isn't that expensive, and besides, the XT-class disk controllers can't, in
general, support 1.2MB or 1.44 MB floppies.

These products don't really work any *slower* on the AT than on the XT, 
just slower relative to the *rest* of the system than the 16-bit parts.  
Again, if you aren't interested in performance, why are you buying an AT?

> This then brings up the other point, some of these new cards you may have to
> get (memory or disk controller) are too tall and will not allow you to put the
> cover back on if it conforms to a standard XT case dimensions.

This is a good point, and it might also be worth mentioning that some PC's
are not only shorter but also not as deep, so that you may not be able to
use full-length cards in some PC's.  You must make sure that *both* 
dimensions of the cards will fit.  Also, more rarely, some cards are fairly
thick (hard-cards, since they contain a small hard disk, are particular
offenders, thougth there are others), and may interfere with the use of
neighboring slots. 

						Bruce C. Wright