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PC100 & PC133 sdram memory together??

My question is will a stick of pc100 sdram and a stick of pc133 sdram sodimm, both 256mb work out ok in a laptop??
I installed them and laptop seems to be working ok.
What are the shortcomings of this? is it ok?
4 Solutions
The faster memory will be forced down to the slower speed...
well depends on  couple of things
firstly if a new stick of 100 it will probley be able to run at 133
if a slightly older stick it will be running at 100
so if you stick both in the pc will be forced to the lower speed  of the 100 memory

well if your pc only takes or runs should i say at 133 this will cause to bomb every now an then.

  But normally will pick speed up directly from chips (ie 100 or 133 ) and cause entire memory system to run at 100 instead of 133
but in real terms your not talking a massive amount and unless doing some serious work (cad etc etc or games) this will not make too much diffrence
when the pc boots it may say what speed runnning at if 100 then it has slowed a bit  if says 133 then i has accepted that it can run at 133 anyway
if you mix up your memmory, your risking possibale constant freezing in your OS. also check out your bios too, because your bios might have an option of memmory installed  100 or 133, this has to be set right but that can't happen with mixed memmory. on the whole not a great idea.

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You are OK if your computer BIOS allows you to set the memory speed at 100, or has set it for you.  Most memory chips have SPD eeproms (little chips that tell the BIOS the memory's speed, voltage, timings, etc), so your BIOS likely will recoginize the slower memory, and run BOTH sticks at the slower speed.  If you can enter your CMOS/BIOS and check what speed your memory is set at, I would recommend keeping it at 100.  If your computer works now, however, then it works.  Don't fix what's not broken.  I don't think you are risking 'constant freezing in your OS' with memory such as this.  (Dual channel boards would be another matter entirely.  You don't have that problem.)
Wow, pc100/133... seems ancient nowadays ;)  

Some of my systems that run a mix of pc100/133 have their ram speeds set solely by the Front Side Bus (FSB) speed settings in my BIOS.  On my P3-733MHz machine, this means all my ram runs at 133MHz, regardless of the memory stick's speed rating.  On my P3-500MHz, all my sticks run at 100MHz. again, regardless of the memory's actual rating.

Basically, if you have a 133MHz FSB, and pc100 memory, you're running your memory overclocked (potentially unstable, run something like MemTest86 to test its reliability).  If you have a 100MHz FSB, and pc133 memory, the memory is underclocked, and I have never heard of this being a problem.
The PC133 will run at PC100. That's a safe bet.

Please check the nano second rating on each chip. I've seen too many unstable systems because chips run at different access speeds.
I had to get somebody some additional pc100. Compared to pc133 quite expensive, so a asked a few people.
All advised me not to use pc133 in on a MoBo requiring pc100. The early pc133 modules were backward compatible, but the current ones supposedly are not...?!

Like to see your responses..... did I pay too much?
On desktops, high-density RAM modules are a problem, because old motherboards don't have the additional address lines to handle them.  This is a more important issue than whether it is PC100 or PC133.  See this thread from AlbertaBeef:
It also depends on the laptop. Some laptops that need PC100 will not work with PC133, or will only work with certain brands of PC133. If you tell us which laptop you have, like make and model, we can find out what memory controller it has, and what speed it really wants, and can search for others' experiences.

My guess is you've got a 100MHz bus system and since the PC133 in it not works, it should keep working just fine for you.

(My laptop has a 100MHz and does NOT like PC133 parts. Upgrading the RAM was uncomfortably expensive.)
what can happen is what heppened to me....
worked fine for 5 or 6 months and then........LOST ALL MY WORK, messed up te laptop which had to be sent to compaq and they weren´t able to fix it.

DON´T DO IT !!!! trust me ! it might work now but just wait a few weeks or months.
ive had no probems mixing these 2 together but all post mentiond above are correct
and of couse it would depend mostly on the type of ram you get and the mfg
there wont be any shortcomings as such .... just that your 133 mhz memory will run at 100 mzh ... also just for confirmation if ur motherboard support 133 mhz .. everything will work fine for sure ....
ermel: Generally speaking, it's best not to mix different types of memory if you can help it. But, if the laptop is working properly and is *stable*, it worked out in your case, and there's nothing to worry about.

CRAK: you were correctly informed. Some PC133 modules will just not work at 100MHz, period.

There are motherboards which can work with both types of modules, but if one of the them is PC100, both must run at 100MHz (overclocking notwithstanding), and this is a problem if the PC133 module will only run at 133MHz. I have experienced this personally.

The proof is in the pudding.
Thanks for the confirmation, Anton74.
ermelAuthor Commented:
I Laptop is an IBM T20 and recommended ram is PC100 but it seems to be running well with the PC133 and PC100 ram together in there. Thanks to all....I divided points as best I could...........if laptop acts up I will inform all.
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