Mixing PC100 and PC133 RAM

[Pikey 0]

Hi all

 

I've just run a search on this and found nothing particularly telling, so here goes.

 

I've just 'upgraded' from 256MB PC100 SDRAM (in 128/64/64 modules) to a stick of 256MB PC133 SDRAM. Now, I have noticed a slight improvement in performance, but I could be imagining it!

 

My question is, was the upgrade worthwhile in terms of pure speed alone, or would I be better off forsaking the speed increase and making use of the leftover 128 and 64MB PC100 sticks and pumping it up to 448MB for a better setup, and would it be 'safe' to do so?

 

I am running Windows 2000 Pro and perhaps could use the extra memory.

 

I guess it's a question of quantity vs quality really, but does the speed increase of PC133 justify not using the leftover RAM?

 

(It's a VIA KT133 chipset mobo BTW, w/an 1Ghz Athlon)

 

Any opinions?

 

Cheers

[Atreyu 0]

I've done this before with absolutely no problems.

 

Just keep in mind, your RAM can only run as fast as your slowest stick. So even though you have pc133 sticks in there, if you have pc100 your pc133 are only gonna be able to run at 100 (or 112 in my overclocked case).

 

Otherwise you should have no problems at all. You'd prolly see a greater improvement in performance with 400+ megs of mixed RAM than you would with 256 megs of pc133 RAM.

[HELLBRINGER 0]

I did that too... Worked great... I would do it. The more RAM the better.

[Busby 0]

Use your 256MB RAM or more for a little bit then switch to 128MB, you'll notice a HUGE difference, I know I did when I went down to 128 from 256.

[ValkyerieK7 0]

I noticed the difference too. 256 is definitely the sweet spot for power users

[Ultrix 0]

The simple answer:

mixing will work in your case.

 

The technical answer:

the PCxxx rating of ram is the speed it is guranteed to operate at. PC66 ram rould run at 66mhz, PC100 will run at 100mhz and 66mhz, and PC133 will run at 133, 100, and 66mhz. The speed of your ram is determined by your front side bus speed. Therefore, if you are running 100mhz fsb (which i think you are because you had pc100 in there origionally), when you added the stick of pc133, it is running at pc100 speed. SO in theory you should see ZERO performance by swapping out the pc100 for the pc133. However, there are other ram specifications that make ram faster and thats the CAS rating. CAS2 ram will run faster than CAS3 ram, because it takes 2ns to do a ram refresh, not 3ns. (dram's design is nice in that it takes one transistor and one cap for each bit one wishes to write. however the with a cap, this requires the storage modules to be recharged, if you write a 1 or 0 to a bit in the ram and dont recharge it, the data disapears as the cap looses charge. The CAS rating is how long it takes for the refresh. (and some other timing issues too). Basically, 2ns is faster than 3ns so cas2 ram is faster. If your pc100 is cas3, and you replace it with your pc133, run it at 100mhz fsb and cas2 setting, it will be slightly faster.

 

The bset thing to do is use a much ram as you can, and tweak the cas settings till you find a stable one (try 2, if it doesnt work, go back to 3). But if all your ram is rated at cas2, make sure thats what you are running, you will benefit.

 

The other thing you can do to get more speed is this:

 

Your kt133 chipset runs 133mhz fsb. If you can unlock your 1ghz athlon, drop the multiplier down to 7.5, and run it at 133mhz fsb. The net processor clock speed change will be zero, but the bandwidth to the processor will be 33% larger. This will force your ram to run at 133mhz also, giving you more ram bandwidth. However, your existing pc100 ram might not run at 133mhz. But the overall increace in bandwidth will result in faster performance. In my opinion, the best thing to do is run 133mhz fsb with 256mb of ram. If you can't, put as much pc100 as you can into your system and run it the way it is. It will work just fine.

 

Hope i didnt confuse you too much

 

Ultrix

[Brian Frank 0]

The only problem with Ultrix solution is that the KT133 chipset has some problems with 133MHz frontside bus apparantly. That is fixed with the KT133A. On Via chipsets, you can run the RAM asynchronous to the front side bus, providing that all the RAM is capable of doing so.

The part about dropping the multiplier and raising the fsb is correct tho.

There is a thing I've heard improves performance, but I really can't tell how much, if any, it really does. Supposedly, the best way for the ram to be installed is the largest sticks of ram in the first dimm slots and progress backwards. Again, I can't really tell a difference.