I would like to expand RAM in my 486sx.  I currently have 4 meg and 
when the memory chips were bought they were listed as "SIMM 1x3 70ns"
I assume the 70 ns means a speed?  is that right?  What does 1x3 mean?
Also, I have 4 of these installed in the only 4 slots available.  What
should I buy to upgrade to 8 MEG?  Also, where is the best place to buy it?
Finally, how do I protect the new chips from static when I put them it
and similarly how do I protect the old ones for possible use by someone else?
Thanks

15 responses total.

Let me give this a shot.  The 1x3 means that you have 1 meg of
memory per simm and there are 3 chips per simm (as opposed to 1x9
simms).  Some computers are more fussy than others about how many
chips per simm.

The 70 ns is the speed in nanoseconds.  To upgrade to 8 megs, I'd
check the book to see if you could get two 4x3 or 4x9 70ns simms.
If you can, it will be easier to upgrade the next time.  If not,
get four 2x3 70ns simms.

Books have been written about the best place to buy things.
Personally I'd check Competitive Computer Systems.  They have
some sharp people who will take the time to answer your
questions--and they have good prices.

Concerning static electricity, it's important to ground yourself.
I usually leave my computer plugged in to a power strip which I
turn off.  That way everything is still grounded.  I usually
touch the case the whole time I'm working with anything inside
it, so I can't build up a charge.

To protect the old simms--I put them in the package that I got
with the new ones.

Carl - Thanks a lot I really appreciate your advice.  
FYI one person told me to take my shoes off while working on the computer
to prevent static.  (maybe - ? )

Those SIMMS are 8 bits wide, you can't just put 2 in. I won't work. The
486 has a 32bit wide data path, so you need 4 SIMMS. It's unusual  for a
motherboard to only have 4 SIMM slots, most of them have 8. If you only
have 4 slots you have to fill them all with either 1 meg simms or
4 meg simms, for a total of either 4meg or 16meg. I don't think
anybody makes 2meg simms anymore. Besides, even if you could find them,
it would probably be more cost effective to go with 4meg simms. The volume
would be so low on 2meg simms that they would probably be expensive.

You should definitely check to see what your computer needs.  It would
be unusual for it to *just* need ?x8 sims - PC's traditionally have
parity ram, so the word size is usually some multiple of 9 (9, 18, 36
bits) wide.  Macintoshes have traditionally had neither ECC nor parity,
not an unreasonable design for a PC.  Unix (and other mini & mainframes)
often have ECC memory, and even wider memory words -- 40 bits is one
possibility there.

  I gather most recent PC motherboards allow paritied or non-paritied RAM,
but it's definitely worth checking your manual before you buy.  If you want
used prices, or want to scrounge a bit, and have access to Usenet, check
misc.forsale.computers.memory...you should be able to find paritied SIMMs
for $25 a meg or so.  New retail prices tend to be closer to $40 a meg.
The best guard against static is a wrist strap that's wired to a ground.
Other tips I've heard: touch your PC's power supply before you touch your
SIMMs, and keep your hands a little moist (wash them first if they're dry);
but I'm not sure how effective these are.  Another thing you can do is try
to hold the SIMMs by the edges.  I wouldn't worry about it too much unless
you get static shocks from doorknobs a lot.

PC compatible machines use 9-bit memory almost exclusively. I have never seen
a PC that uses 8-bit memory. If they exist, they are very rare.

I've now heard of one "pc compatible" that uses 8-bit memory; it's made
by Apple and plugs into a power Macintosh.

On some PC's you can off the parity bit and use 8 bit SIMMs.

A lot of the newer PC motherboards can use the noparity SIMMs.  Why?
a.  memory is more reliable?
b.  It' a lot cheaper to give up that last bit, esp. over 8 Meg or more.

Okay, here's my question.  A friend of mine has a 286 machine.  He's
looking at those Make-it-486 chips that sell for $99, and has asked my
advice.  Well, it's occurred to me that 386SX/40 motherboards are only $75
now.  The question is, will the memory from the 286 even work on a 386/40
motherboard?  Obviously it's considerably slower than modern memory.  New
memory would raise the price of the whole package quite a bit, though.

So:  will it work?  Or is the Make-it-486 a better option?

I've heard you can get 486 motherboards for $100 now.  I'd avoid the weird
upgrade chip, myself.  And just how much *more* memory will be needed anyway?

It's not a question of more memory....what I want to know is if we can use
the memory he's already got.  RAM is expensive.

What sort of memory does the 286 have.  If it has SIMMs, it should work (as
long as the new motherboard has 30 pin sim sockets.  If it's something other
than SIMMs, it probably won't.

I think it's SIMMS, or I wouldn't even be thinking about doing this. ;)  I
need to install an I/O card for him soon, and I intend to check on the
memory situation then.  Thanks for your help.

Check the speed of the SIMMs, too...there will probably be a "-100" or "-80"
or something on the end of the chip's numbers.  I think 100ns might be too
slow for some 486s.  I've bought 70ns SIMMs for a long time, so I don't
remember the threshold.  By the way, upgrading from one type of SIMM to
another generally doesn't cost all that much.  I've switched some 30-pin
SIMMs to 72-pins SIMMs for under $2 a meg.  Also, new SIMM prices are down
a bit lately...new non-parity 70ns SIMMs were around $18 a meg last week.

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