km@mathcs.emory.edu (Ken Mandelberg) (06/03/89)
Does anyone know any trick for violating the MacOS RAM configuration
rules when running A/UX?
More specifically, we have a number of A/UX machines with 4 1 Meg
simms. A/UX (with networking and X) runs much better in 5 Megs than 4.
On MacOS the only memory expansion we can do is add 4 more simms,
either 256K simms or 1 megs simms.
Neither of these options are attractive. 4 extra 1 meg simms per
machine is more than we can afford. On the other hand investing a lot
in 256K simms is wasteful, since they cannot be used if more memory is
added later.
I wish there was a trick that let us just add a 1 meg simm to the 4
already there. Every Unix kernel I have seen (prior to A/UX) has been
very flexible on sizing memory. I don't know what the real issues are
on the MacII, but at the very least MacOS will not boot with 5 1 meg
simms, which gives no way to boot A/UX.
--
Ken Mandelberg | km@mathcs.emory.edu PREFERRED
Emory University | {decvax,gatech}!emory!km UUCP
Dept of Math and CS | km@emory.bitnet NON-DOMAIN BITNET
Atlanta, GA 30322 | Phone: (404) 727-7963rmtodd@uokmax.UUCP (Richard Michael Todd) (06/04/89)
In article <4105@emory.mathcs.emory.edu> km@mathcs.emory.edu (Ken Mandelberg) writes: >I wish there was a trick that let us just add a 1 meg simm to the 4 >already there. Every Unix kernel I have seen (prior to A/UX) has been >very flexible on sizing memory. I don't know what the real issues are >on the MacII, but at the very least MacOS will not boot with 5 1 meg >simms, which gives no way to boot A/UX. The reason you can't just stick in a single 1meg SIMM is due to the hardware design of the machine, NOT the OS involved. The data bus is 32 bits wide and the SIMMS are only 8 bits wide. The memory bank has to be able to present a full 32-bit word to the CPU whenever the CPU accesses it. When you plug in a single SIMM into the memory bank, the CPU tries to fetch 32-bit words from memory and gets 8 bits of data and 24 bits of garbage. It just won't work. That's the price you pay for having a real 32-bit processor in your machine, instead of an 8088 :-). -- Richard Todd rmtodd@chinet.chi.il.us or rmtodd@uokmax.ecn.uoknor.edu aka ...!sun!texsun!uokmax!rmtodd "MSDOS is a Neanderthal operating system" - Henry Spencer