What happens if I stick PC133 memory into a PC100 slot?

[GizmoFreak]

A friend of mine has a ThinkPad T20 laptop which takes PC100 SODIMMs. However I came across a free PC133 SODIMM RAM chip. Can I install this on the ThinkPad and expect no adverse effects?

 

[MattTheTech]

Many times PC133 will work fine at the lower speed. It will not hurt to at least try anyway.

 

[imported_Mitchell]

Nothing, faster memory will always work in a slower buss.

The opposite is not always true though

 

[GizmoFreak]

Great, extra 128MB for my friend

 

[sunase]

I actually tried this recently. The motherboard I had popped up an error message on bootup that it couldn't understand the SPD and that it was going to run it at 100MHz anyway. I checked the RAM in a slightly more modern computer and CPU-Z reported that it had SPD values for both 100MHz and 133MHz, so it was just the motherboard not able to read it, not the RAM. Anyway, only drawback of using it in that older computer is that the motherboard is running it at CAS3 when CAS2 would be fine according to the SPD (and there is no BIOS setting to override).

So it worked for me anyway, at the slight cost of some latency. I hear some older boards don't like high density RAM, though, which is something you might want to look out for.

 

[Harvey]

Originally posted by: Mitchell
Nothing, faster memory will always work in a slower buss.

That's not necessarily so. There are compatiblity issues with newer PC133 memory and older PC100 RAM slots.

You can safely try it. It won't smoke anything, but it may lock up the machine.

 

[William23]

Originally posted by: GizmoFreak
A friend of mine has a ThinkPad T20 laptop which takes PC100 SODIMMs. However I came across a free PC133 SODIMM RAM chip. Can I install this on the ThinkPad and expect no adverse effects?

It will cause a nuclear reaction the likes this planet has never seen....DON'T DO IT!!!!!


It'll just run at the lower speed,I've done it many times

 

[redbeard1]

To be careful, you could install the ram, then boot to Memtest86+ right away. Then you don't risk crashing while going into your OS.

 

[The Sauce]

It would be like matter and anti-matter - the entire universe wound instantly get sucked into your computer.

 

[VirtualLarry]

Originally posted by: Harvey

Originally posted by: Mitchell
Nothing, faster memory will always work in a slower buss.

That's not necessarily so. There are compatiblity issues with newer PC133 memory and older PC100 RAM slots.

You can safely try it. It won't smoke anything, but it may lock up the machine.

Yes and No, the only issues are with the BIOS being able to read and comprehend the SPD info, and program the associated chipset memory-controller registers properly, and also compatibility issues between "high density" SDRAM, vs. "low-density" SDRAM. Older chipsets with older memory-controllers (i440BX) couldn't handle the newer memory chips, so sometimes the DIMMs only appeared to be half the size that they should be, or they simply wouldn't work.

Those issues are independent of whether or not the memory is rated to run at PC100 or PC133 speeds, but most PC133 RAM that you find nowadays is "high density", and therefore does cause a problem when attempting to use it on older boards. So you're basically right, but the problem is not the speed, but the internal memory-chip organization of the chips common to that generation.

Edit: Mixing memory speeds is not advised, but for best results, put the slower speed/higher-latency memory into the first DIMM slot, as some BIOSes/chipsets only check the first slot, and set the timings for all of the memory that way. Forcing it to use the slowest timings, ensures that all of it will run, all other things considered.

 

[techwanabe]

Originally posted by: Harvey

Originally posted by: Mitchell
Nothing, faster memory will always work in a slower buss.

That's not necessarily so. There are compatiblity issues with newer PC133 memory and older PC100 RAM slots.

You can safely try it. It won't smoke anything, but it may lock up the machine.

Harvey,

Save the politics for another forum please.

As for the PC133 memory ... I have never had a problem in the some 50 computers I've installed memory in.

 

[CraigRT]

memory is usually fully backwards compatible. (not always but most of the time)
i put PC133 in Pentium 200 computers at work.... works

 

[Arcanedeath]

Really the only thing you need to worry about using PC133 in older systems is that if it's "High Density" eg not 16x8 then you may have issues w/ I440BX, I440LX, and some SiS based systems only seeing 1/2 the memory or not being seen at all.

 

[GizmoFreak]

Well the ThinkPad T20 takes 16x64 and the PC133 chip in question is also 16x64. I put the chip in and the memory registers. And I haven't observed anything unusual so far.

 

[dnoyeb]

Faster comaptible memory will always run in slower compatible slots.

With PC100 and PC133 however, the issue is not the memory speed, but the number of chips. The PC133 was made in a time where they started making denser cards. So you could find a larger number of chips on the 133 than on the 100, and your computer may not like that.
As for damage, I dont think you can cause any. If it works, your good to go.

 

[Kingofcomputer]

16x64 means the module is 128MB,
for intel chipset, the 8 or 16 ram chips used on the 128MB module must be 16x8 (16MB) or 8x8 (8MB), cannot be 32x4 (16MB) or 16x4 (8MB).

 

[Harvey]

Originally posted by: techwanabe
Harvey,

Save the politics for another forum please.

Politics? What are you smoking besides incompatible RAM? :roll:

VirtualLarry -- Thanks for a good explanation of the reasons for the incompatiblity I noted.

 

[techwanabe]

Originally posted by: Harvey

Originally posted by: techwanabe
Harvey,

Save the politics for another forum please.

Politics? What are you smoking besides incompatible RAM? :roll:

Looks like you've been smok'in - er, can you say short term memory loss?

Talking about your 3 line sig buddy - duh!

 

[imported_Skorpio]

Depends, how old the PC133 ram is.

PC133 should work with PC100.

Recently I upgraded my PIII which could only officially accept PC100 ram chips. Had a problem accepting newer memory modules. Anyways I bought a pny pc100 256 mb mem module labeled pc100 on the box. However using motherboard testing, showed it was infact pc133 and it said so on the sticker on the mem module.

The thing to know is that if the PC133 is high density or low density like virtual larry and arcanedeath said. Also the number of chips on the module, such as (16X8)

What would happen is that if you manage to get to windows without a blue screen...then your good.

Otherwise...a blue screen

I doubt you would get permanent effects on to your computer, unless you put it in the wrong way..lol. So try...it..hopefully it works. good luckl