Mixing PC2100 and PC2700 RAM

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BigMacSangwich · #1 Post by **BigMacSangwich** » Tue Mar 04, 2008 4:28 pm

I have read that mixing RAM with different cas latency will result in all your ram having the lowest cas latency. Does the same thing apply to using different PC#### RAM? I have a 256mb PC2100 module along with a 1gb PC2700 module. Would I have a faster computer if I took out the PC2100 module?

aaa · #2 Post by **aaa** » Tue Mar 04, 2008 5:05 pm

Most of the time the amount of ram is more important than the speed. The speed difference is teeny, and the slowdown that happens if you happen run out of ram is far bigger.

#3 Post by **richk** » Tue Mar 04, 2008 6:08 pm

It depends on the machine. T40 machines run at PC2100 (266 mHz) speed all the time. T41/T42 machines run at PC2700 (333 mHz) speed, but a PC2100 module mixed in will cause both slots to run at PC2100 speed.

BigMacSangwich · #4 Post by **BigMacSangwich** » Tue Mar 04, 2008 6:57 pm

If I rarely utilize 100% of 1gb of RAM anyways, do you think I should remove the 256MB module just to get slightly faster performance by having the PC2700 speed? What I'm after is faster loading of applications, and not so much having a lot of stuff open at once.

Or will the difference not be noticible at all? The difference is 600mb/s right? That sounds like a lot to me. (I have a T41 Pentium M 1.6ghz)

aaa · #5 Post by **aaa** » Tue Mar 04, 2008 7:00 pm

Faster loading of applications depends more on the hard drive. You only notice the difference when running something that uses the CPU, even then it is still pretty small.

BigMacSangwich · #6 Post by **BigMacSangwich** » Tue Mar 04, 2008 7:09 pm

ok I guess I will stick with the 1.25gb of RAM. Now that I think about it, I didn't notice that much of a difference in application startup speed except when a lot of processes were running, when I had to downgrade from 2x 512mb PC2700 to 2x 256mb PC2100 over the weekend.

thanks for the quick replies =)

sjthinkpader · #7 Post by **sjthinkpader** » Wed Mar 05, 2008 9:03 am

This because the CAS low to data out is actually all about 7.5nSec. The PC2100 has a shorter CL and PC2700 has a longer CL. This CAS Access time value really hasn't changed for several generation of RAMs.

You will only notice speed increase when the data access page length is sufficiently long. Then the faster clock speed comes into play.

See the last post in this thread:

http://forum.thinkpads.com/viewtopic.ph ... highlight=

Mixing PC2100 and PC2700 RAM

Mixing PC2100 and PC2700 RAM

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