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pc100 and pc133

Last response: in Memory
a b } Memory
July 30, 2001 12:56:57 AM


i'm just wondering if it is safe to have a pc100 and pc133 stick of ram on the same mobo. Or are there any disadvantages...


More about : pc100 pc133

July 30, 2001 2:06:58 AM

sure its safe..... pc133 is backward compatible. if your system is running a 133 fsb and you add slower ram, youd be in trouble though. im assuming you are adding the 133 to a system with 100 already....

...and i would have gotten away with it, if it weren't for you meddling kids...
a b } Memory
July 30, 2001 5:09:51 AM

i don't get it...

wouldn't having a 133 and adding a 100 be the same as having a 100 and adding a 133...

it still ends up with the combination...

please explain, thanks.
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a b } Memory
July 30, 2001 5:22:52 AM

No matter what it will end up running your memory at 100. IF your system requires PC133, PC100 won't work. If your system requires PC100, PC133 will work.

Video killed my Radio Card!
July 30, 2001 7:48:37 AM

actually it shouldnt matter whtever memory you put in, the core problem is that would the system be stable enough???

if you have a 133 MHz processor and you put a 100 MHz RAM into the board you have a slower system that the memory will run at 100 MHz while your proessor will run at 133. actually, this is this is the thing shown by Intel D815EEA2 board when I put PC100 128 MB stick into it for a 800/133 processor. i guess the 815 does decouple the CPU and memory clock and lets both run ar their speeds. else the processor should have run at 600! thats (6x100=600) against (6x133=800). i dint check it with any utility of course since i immediately replaced the PC100 with PC133. will check though.


<font color=blue>die-hard fans don't have heat-sinks!</font color=blue>
July 30, 2001 8:03:44 AM

well, what if you put sticks of different speeds at a time?

i have noticed some performance drop and frequent BSOD occuranced when I put two PC100 sticks from different manufacturers on my K62, and even more when I tried putting PC66 DIMM into it.

basically the chipset manuals say that it has a separate set of timing registers for each of the DIMM slot and the it if filled with the contents from the SPD chip on the module from that slot. this should be okay and sticks with different speeds should work well, but this isnt what we see.

better is to get sticks of same speed as that of the processor from a good manufacturer, as far as possible try to have a single one, and if you do need to have more than one get it from the same manufacturer. maybe the SPDs from different manufacturers are programmed differently for similarly rated modules.


<font color=blue>die-hard fans don't have heat-sinks!</font color=blue>
July 30, 2001 9:38:15 AM

I was running 2 x 32MB PC-66 with 128MB PC-100.
Then I was running 1 x 32MB PC-66, 1 x 128MB PC-66 and 2 x 128MB PC-100.

Worked fine!

Found that when I removed all the PC-66, the system sped up slightly.

"Now drop your weapons or I'll kill him with this deadly jelly baby." :wink:
a b } Memory
July 30, 2001 6:25:59 PM

Only a few chipsets support the 133/100 FSB/memory clock split (such as the i815). For everyone else, running PC100 means that the FSB will be at 100 or less, or if they try to run a 133FSB it will lock up.

Video killed my Radio Card!
a b } Memory
July 30, 2001 6:41:03 PM

You were probably trying to overclock the PC66 to 100, bad idea. We are talking BACKWARD compatability, not FORWARD compatability. If you suffered from instability with two different brands of PC100, either one stick was bad or set to the faster timings of the other.

Video killed my Radio Card!