RAM question: mixing memory of different speeds

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I recently got a buttload of computer parts from work. I have a working computer and a slightly ancient mobo - Asus P4S533 Anyway, I also got a bunch of memory as will. I have 1.2 gb of 333mhz and 1gb of ddr400 ram (in 2 sticks). I was able to boot up the computer with all the memory in.

My question is - what is the difference between all the speeds? Obviously the mobo supports all of them, so what is stopping me from running all of them at the same time? Is it better to run just the faster stuff with only 1GB? I'm not too terribly familiar with memory speed; I just want to make sure I won't blow something up...the computer was free, but I'd hate to bork it up. Thanks for all help
not sure, but i have a similar question. i am considering taking out the old ram chip from my parents old pc, its not much, but as long as its the same type of memory, would it hurt if i put it in just to add a little boost? i already have one gig of ddr2 ram
Do Ya Feel Lucky.....?

Some board are more tolerant that others of installing mismatched RAM. In all cases, all of the installed RAM will run at the speed of the SLOWEST module. IE; if you put in PC2700 (333) Mhz and PC3200 (400 Mhz) all of the RAM will run at 333 Mhz. Intel dual channel boards are fairly forgiving. However, in a dual channel board, you must match the RAM with the correct channel and socket. A dual channel board generally will have two RAM sockets per channel. (4 total) Each channel will have 2 different color sockets. To run mismatched speed RAM, (which I am in the computer I'm using to post this), I would (and did) populate the sockets like this; I used 2 256MB PC3200 DIMMs, 1 in each of the boards blue sockets. These were the ones the computer came with. Then I installed 2 512MB PC2700 DIMMs, 1 in each of the black sockets. The rig runs fine in dual channel, but at PC2700 (333) Mhz. Such as this is, remember that the channels AND sockets are balanced in pairs. This configuration nets 1.5GB of memory, 768 per channel. The 2 512MB DIMMs are even different manufacturers. however they are the same speed.

I wouldn't go out of my way to do this, but if you have the modules already, why not give it a shot. Remember your anti-static strap.
The worst thing that can happen is you'll have an unstable system. The best thing that can happen is you'll have a stable system with more RAM.
From what I can tell, basically combining RAM slows it all down to the slowest speed. What is the difference in speed? Is it very noticeable. Like, if I went from 400mhz to 333mhz, would it be worth the extra 512mb?
Maybe a Little But........,

When a computer runs out of physical RAM (the DIMMs), it uses the swap file. This is a section of the hard drive used by the OS as "virtual memory". It's a lot slower than actual memory. After all, you're writing information to and recovering from the HDD, a mechanical action, whereas with the installed RAM s*** happens at or near the speed of light. OK, thats an exaggeration, but as soon as you write to the HDD, you do drop out of warp, so to speak. So, you probably wouldn't notice the difference in speed between 333 and 400Mhz RAM, but you'll definitely notice the speed difference when you run out. Better to have more slightly slower RAM than just a little bit of faster. Much better.
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