🚀 go-pugleaf

Stuart Baldwin wrote:
> 
> I have in my possession a 1994 vintage, Morgan Generic-badged, IBM Blue
> Lightning 486DX2/66.  I plan, if possible, to add a network card and use
> it as a Linux server/router/etc. and would be interested if anyone here
> is familiar with these machines and can warn of any potential problems
> or eccentricity or can point me at a good online source of this sort of
> information.

Don't know much about the actual IBM hardware itself but it will certainly
make a decent enough server/router even with only 8MB of RAM.

> 
> It has 4x72 pin SIMM sockets, currently populated with 2x4MB SIMMS.  I
> have a spare 4MB SIMM from a more conventional 486DX4/100 motherboard
> (which won't fit the IBM case) that I could add to the existing 2 if a)
> it is compatible and b) these SIMMS can be added singly, rather than in
> pairs.  If I don't get any info on this I plan to just plug the extra
> SIMM in and see what happens.  Am I likely to cause any damage by doing
> this?

You are unlikely to damage the mobo by adding a single SIMM but an odd
number of SIMMs just won't work! It will do one of 2 things:
1) Only recognise the original amount of memory made up from the pairs
already in there (ie your existing 8MB) OR
2) Not boot at all!

SIMM stands for Single In-line Memory Module and they *MUST* be added in
pairs. DIMMs on the other hand are Dual (or is it Double? - I forget - means
the same anyway!) can be added one at a time. I have 3 x 64MB PC100 SDRAM
DIMMs in this machine. But in my older boxes I have 4 x 16MB SIMMs or 2 x
32MB SIMMs.

The reason you need pairs of SIMMs is all down to the way the memory is used
by the system. AIUI with SIMMs the memory is written to by interleaving
between the pairs (eg 1 with 2 and 3 with 4 on a four socket mobo). Anyway
this is far too complicated to go into at this time on a Friday
night/Saturday morning!

Incidentally how come you have a single SIMM that is spare from this other
mobo that won't fit the case? That machine would also need pairs!
-- 
Richard Howlett

mailto:richard@howie.org.uk