beware of memory addressing conflicts; info

[Karl Lehenbauer]

Just a note...

If you're running an AT clone that has more than 640k on the motherboard,
remember that only the first 640k is contiguous, the next 384k is 
reserved for i/o and various other stuff.  For the example of a 1 meg
motherboard, the first 640k starts at address zero, but the last 384k
starts at 1 meg (not 640k), meaning that the first external memory board
needs to start at 1.375 meg rather than at 1 meg.

I had this problem when I first got my system.  It would work at 6 MHz
but not at 8 MHz.  At first I thought the external memory board just wasn't
fast enough.  What was really happening was there was 384k of address
space being overlapped by two sets of RAM and it would still manage
to work at 6 MHz.  Not only did remapping the card fix the problem,
I got another 384k in the address space as well.  

Problems like this are reasons to buy genuine IBM or really mainstream 
clones rather than arbitrary no-pedigree clones.  These problems really 
burn a lot of time in figuring out what's going on, and particularly 
since we're using Unix, we don't get a lot of support from the dealers,
vendors, etc.  Of course we don't buy the real thing because we're too 
poor, but "enhancements" provided on systems that don't get real widely
distributed can result in major headaches.
-- 
"Lack of skill dictates economy of style." - Joey Ramone
..!uunet!nuchat!sugar!karl, Unix BBS (713) 438-5018