🚀 go-pugleaf

thamilto@fnugget.intel.com (Tony Hamilton) writes:

>HI. Just bought a 486-33DX machine. For reference, it's an Intel _computer_...
>I work at Intel and bought one on an employee offer. Anyway, it came with
>4MB installed, in a 32-pin SIMM or something like that (I'm new to memory).

>The system also comes with 2 banks of 4 9-pin SIMM sockets, for either 1x9
>or 4x9 SIMMs (I still hope I'm getting these pin numbers right. It's the best
>I can remember - I don't have my manual with me). Well, anyway, the manual
>stated that you can mix and match SIMM types, as long as each bank of 4 has
>all the same, and is either all full or all empty. In addition, you can pop
>in an 8MB SIMM apparently in place of the 4MB one. Anyway... the manual
>suggests 80ns RAM, or faster. Because it was available and _very_ cheap, I
>popped in 100ns 1x9's in all 8 extra sockets, giving me 12MB total. Everything
>works fine, and I can verify the RAM is working for my applications which
>can use it.

>My question is: every tech person I talk to says not to do this, but they
>can't explain the reasoning behind that caution. I've heard it may have
>something to do with the bus and addressing, but I don't see any problems with
>the integrity of the memory. Should I be able to get away with this, or is
>there still a need for concern?

Yes there is reason for concern. While your system seems to run OK
you could get occasional random memory errors. Your system could
crash at any time without warning.

The memory access speed is the time it takes from when the processor
puts the memory address out to when the memory parts to put out the data.
You processor will wait 80ns from when it puts out the address to read
the data lines. But the memory parts could take up to 100ns to get
the data out. So its possible that when the processor reads the data
lines the memories haven't put their data out yet. The processor then
will use whatever random data was on the data bus and your program
gets messed up.

I would suggest removing the slow memory, you are just asking for trouble.

valid data
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Robert Wiegand - Motorola Inc.
motcid!wiegand@uunet.uu.net            uunet!motcid!wiegand
Disclamer: I didn't do it - I was somewhere else at the time.