New memory in old PC?

[John Brock]

What are the odds that I can take a spare 128MB memory module,
yanked from a recently bought PC, and install it into an old Pentium
PC (ca. 1997)? The old PC currently has 80MB, and obviously I
can compare the old and new memory to see if the new module will
fit into the old socket. But if fits does that mean it will work?

Actually the question I am most interested in is this: if I install
the new memory and the machine boots up afterwards and everything
seems to be OK does that mean everything really is OK? Or might
there be subtle problems which will show up later?

Also, I've seen comments to the effect that having mismatched memory
modules (e.g., different speeds) can lead to problems. If the new
memory works should I dump the old memory, or is it safe have both
in the same machine? Are there any good web sites which would
address such issues?

My inclination is to play it safe, so I'm looking for strong
assurances that this sort of thing is kosher, that it's done all
the time, and that there are no hidden traps. The old PC is going
to end up in the hands of someone who is not particularly technical,
so if what I'm thinking about is questionable then I won't even try.

 

[Rob Stow]

What are the odds that I can take a spare 128MB memory module,
yanked from a recently bought PC, and install it into an old Pentium
PC (ca. 1997)? The old PC currently has 80MB, and obviously I
can compare the old and new memory to see if the new module will
fit into the old socket. But if fits does that mean it will work?

Actually the question I am most interested in is this: if I install
the new memory and the machine boots up afterwards and everything
seems to be OK does that mean everything really is OK? Or might
there be subtle problems which will show up later?

Also, I've seen comments to the effect that having mismatched memory
modules (e.g., different speeds) can lead to problems. If the new
memory works should I dump the old memory, or is it safe have both
in the same machine? Are there any good web sites which would
address such issues?

My inclination is to play it safe, so I'm looking for strong
assurances that this sort of thing is kosher, that it's done all
the time, and that there are no hidden traps. The old PC is going
to end up in the hands of someone who is not particularly technical,
so if what I'm thinking about is questionable then I won't even try.

A PC that old might very well have existing RAM that runs at a
higher voltage than more modern DIMMs. There might be a
jumper on the motherboard to let you select the DIMM voltage -
if there is one, set it at the lowest value if you want to
go ahead and try the new DIMM.

I would just remove all of the old DIMMs and try the new one
all by itself. The risk to the motherboard is negligible, but
the voltage issue might put the new DIMM at risk. If the
system POST doesn't start up as usual, just power off quickly.

Aside from the voltage issue, there is a good chance that
the memory controller on that old motherboard will not know
how to deal with higher density DRAM chips on newer DIMMs.
In that case, the POST will report the new DIMM as being
either 1/2 or 1/4 of its actually size. Ie., it will report
the new 128 MB DIMM as 64 MB (very likely) or as 32 MB (very
unlikely, but not unheard of.) Some systems are remarkably
stable in a situation like that, while others are extremely
crash prone.

All in all, you are quite safe in trying out the new DIMM and
seeing if it works. If it doesn't, you haven't put the
motherboard or the old DIMMs at risk and you can just revert
the system to its original state. There is a slight risk to
the new DIMM due to the possible overvoltage issue.

 

[GSV Three Minds in a Can]

What are the odds that I can take a spare 128MB memory module,
yanked from a recently bought PC, and install it into an old Pentium
PC (ca. 1997)? The old PC currently has 80MB, and obviously I
can compare the old and new memory to see if the new module will
fit into the old socket. But if fits does that mean it will work?

No, the voltage could be wrong, which would fry the new RAM.

More likely it won't fit/work at all .. 1997 (straining my brains) the
standard RAM was PC66 or PC100 SDRAM, whereas today it'll be PC2700 or
PC3200 DDR. I don't think you could even achieve 80MB (presumably 16MB +
64MB?) with DDR, since I don't recall DDR DIMMS coming in anything as
small as 16MB (although it was a long time ago, so maybe I've just
forgotten).

Actually the question I am most interested in is this: if I install
the new memory and the machine boots up afterwards and everything
seems to be OK does that mean everything really is OK? Or might
there be subtle problems which will show up later?

There might, but if it passes memtest86 (www.memtest86.com) and the
prime95 torture test (www.mersenne.org) then it'll probably work right
on anything else.

 

[Anonymous Joe]

What are the odds that I can take a spare 128MB memory module,
yanked from a recently bought PC, and install it into an old Pentium
PC (ca. 1997)? The old PC currently has 80MB, and obviously I
can compare the old and new memory to see if the new module will
fit into the old socket. But if fits does that mean it will work?

Actually the question I am most interested in is this: if I install
the new memory and the machine boots up afterwards and everything
seems to be OK does that mean everything really is OK? Or might
there be subtle problems which will show up later?

Also, I've seen comments to the effect that having mismatched memory
modules (e.g., different speeds) can lead to problems. If the new
memory works should I dump the old memory, or is it safe have both
in the same machine? Are there any good web sites which would
address such issues?

My inclination is to play it safe, so I'm looking for strong
assurances that this sort of thing is kosher, that it's done all
the time, and that there are no hidden traps. The old PC is going
to end up in the hands of someone who is not particularly technical,
so if what I'm thinking about is questionable then I won't even try.

There's a lot of variables in such a thing like this. The Pentium is using
a 66MHz bus (assuming it is anything 133MHz and over; or 66MHz), so you need
PC66 RAM or better. By better, this just means something that can work
faster, like PC100/PC133, and unlikely that you have it, but the
'overclocker's' ram (ie PC150 [it isnt official]). You can most certainly
use PC100 or PC133 at PC66. I mean, think of it this way, you buy a car
that is well-equipped to go 120MPH. Can you drive at 35mph? Ah,
exactly....

As many have pointed out, voltages is perhaps different. It could be 5v,
although unlikely.

The last thing is if the Pentium's motherboard only accepts EDO or FPM then
it isn't going to work. I hope you already checked out the Pentium's board
and found it is using 168-pin DIMMs (or has the capability to) otherwise it
is all useless.

MOST IMPORTANTLY: since new computers use DDR memory you really have to be
looking in a PC that is older than new. While DDR & SDR memory are
physically the same size, DDR is 184pins & 1 notch. SDR is 168pins & 2
notches. They will not even physically fit together. To find SDR in a new
PC, you'd have to look at very low-end budget PCs, and it would need to be
running a rather slow Celeron.

 

[Stacey]

A PC that old might very well have existing RAM that runs at a
higher voltage than more modern DIMMs. There might be a
jumper on the motherboard to let you select the DIMM voltage -
if there is one, set it at the lowest value if you want to
go ahead and try the new DIMM.

Isn't one of the slots on the ram for voltage? I didn't think the wrong
voltage ram would plug in..

 

[Rob Stow]

Rob Stow wrote:




Isn't one of the slots on the ram for voltage? I didn't think the wrong
voltage ram would plug in..

I have fried a 256 MB PC133 DIMM by swapping it for a 64 MB
PC66 DIMM without remembering to also adjust the DIMM voltage
jumper on the old AOpen Pentium board I had at the time.
IIRC, that jumper selected between 3.0 V and 3.3 V. Luckily
the store let me exchange it and I remembered to adjust the
voltage for the replacement.

 

[steven67@]

I have fried a 256 MB PC133 DIMM by swapping it for a 64 MB
PC66 DIMM without remembering to also adjust the DIMM voltage
jumper on the old AOpen Pentium board I had at the time.
IIRC, that jumper selected between 3.0 V and 3.3 V. Luckily
the store let me exchange it and I remembered to adjust the
voltage for the replacement.

..


PC66 and PC133 SDRAM DIMMs are the same voltage--3.3V.

The motherboard jumper was for 5.0V and 3.3V. 168-pin FPM and EDO DIMMs were
available for 3.3V or 5.0V. 168-pin PCxxx SDRAM DIMMs were 3.3V.

 

[George Macdonald]

What are the odds that I can take a spare 128MB memory module,
yanked from a recently bought PC, and install it into an old Pentium
PC (ca. 1997)? The old PC currently has 80MB, and obviously I
can compare the old and new memory to see if the new module will
fit into the old socket. But if fits does that mean it will work?

If the new module is DDR-SDRAM, which is the most common on recently bought
systems, it'll be obvious that the contacts are different from the old
SDRAM DIMMs and it will not fit in the mbrd slot. If the DIMM fits in the
slot, no damage will be done and there's a good chance it'll work but you'd
have gotten a better answer if you'd told what the current 80MB is made up
of. If there are 8 chips or more on that new 128MB module you should see
the whole 128MB; if only 4 chips you'll probably only see 64MB.

If the 128MB is in fact SDRAM, it'll be a "four-clock" DIMM. My memory is
hazy on the dates here, but some early SDRAM DIMMs, in 16MB and 32MB sizes,
were "two-clock". I *think* that by mid-1997, the transition had been made
to the four-clock standard for all mbrds but if the mbrd is a two-clock
design, you'll only see 1/4 or 1/2 of the actual DIMM size, depending on
how the new DIMM is populated.

Actually the question I am most interested in is this: if I install
the new memory and the machine boots up afterwards and everything
seems to be OK does that mean everything really is OK? Or might
there be subtle problems which will show up later?

There shouldn't be any problems but it'd be worth running memtest86
(www.memtest86.com) anyway.

Also, I've seen comments to the effect that having mismatched memory
modules (e.g., different speeds) can lead to problems. If the new
memory works should I dump the old memory, or is it safe have both
in the same machine? Are there any good web sites which would
address such issues?

It depends on the mbrd. It's unlikely that a mbrd that old can auto-match
to different DIMM speeds based on SPD info and the old DIMMs likely don't
have SPD info anyway. Certainly the new DIMM will allow BIOS setting for
memory speed to be set to the fastest possible. If you have a 16MB DIMM in
that 80MB I'd advise taking it out and run memtest86 on the 128MB DIMM,
with and without the other old DIMM(s). It will report the memory speed.

Take a look at www.crucial.com - there are some useful docs and you can
look up what's recommended by them for the old mbrd to see if it is similar
to the new 128MB DIMM.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??