RAM SIMMs in pairs vs singles

[aratike]

When adding SIMMs to a computer, is it NOT a good idea to add only one instead of adding in pairs? I've heard that to get the best performance out of a memory upgrade involving SIMMs, you need to add them in pairs. Is this true? How much of a performance hit will I be getting if I add only one?

[socalgal]

SIMMS must be installed in pairs.

[Ziz]

It depends on the motherboard. Some boards will take them in singles, some will take them in pairs. Generally, 72 pin SIMMs are used in pairs, 168 pin DIMMs are used individually. In other words, you must always have an even number of 72s in a machine; 2, 4, 6, 8. DIMMs can be any amount; 1, 2, 3, 4.
The other thing to remember with 72 pin SIMMs is that the pairs must be the same, moreso in amount of memory than in speed, but matched speed is preferable too. You can have 2 pairs of 16meg and 2 pairs of 32 meg SIMMs in the same machine, so long as the like SIMMs are next to each other; the 16s in slots 1 and 2 and the 32s in slots 3 and 4, or vice versa. Don't go 16, 32, 16, 32.
If you're using DIMMs, then your only concern is using your slots efficiently so that when you upgrade, you don't have spare memory sticks laying around with nothing to do. Since DIMMs operate individually without concern for the amount in the slot next to it, you can use them in any order you want...32, 16, 128, 64. It's generally a good idea to put the largest module in slot 1, but I haven't heard any die-hard rules on it one way or the other.

Hope all this helps!

[LJE2]

In a 486 motherboard you had a 32 bit memory bus, 72 pin RAM is 32 bit, so you could add 1 simm at a time, when they came out with the Pentium motherboard the memory bus was 64 bits, since 72 pin RAM is 32 bit, it had to be added in pairs, DIMMS or 168 pin RAM is 64 bit memory, the memory bus on Pentium, Pentium II, & Pentium III motherboard is a 64 bit bus so you can add DIMMS 1 at a time. There are exceptions to this in proprietary boards (some early Packard Bell pentium mobo's had only 1 Simms slot, for expansion the rest of the RAM was built on the board and there are a few other exceptions)

[This message has been edited by LJE2 (edited 06-20-99).]

[socalgal]

LJE2 & Ziz - thanks for expanding on the subject. I didn't know there were motherboards that could take only one SIMM!

[sabine urfer]

You usually won't get big performance boosts, when installing a pair of RAM, instead of one. The only advantage would be the possibility of bank-interleaving, which means the chipset can adress one memory bank and whilest waiting for the date, it can simultanly address the other bank...

If you have a "stupid" chipset, like intels VX or TX, you could even get a performace loss, when installing more then 64MB of memory. But thats a different story...

[ctswiz]

There normally isn't any performance-related things for RAMs. The speed is fixed, no matter what you do. I wouldn't try overclocking it either. However, it is best to install RAM in two's because if one RAM chip frys out, you still have the other one. If you only have one, then if it frys, you're gonna lose all your RAM...

[aratike]

I've got an old NEC Pentium 133 w/ a whopping 8 megs of ram (2x4mb 72 pin SIMMs) that I was going to give to my nephew. I would like to overclock it a tad and add some RAM before I do. According to the manual that came w/ the PC, the RAM could be added via a single stick, but it was stated that to get optimum performance, one must add it in pairs. I was going to add a 16 meg stick, but now I am beginning to wonder if thats the best route to go....

[steves]

Some budget Pentium motherboards of that era did have a memory addressing feature that would allow you to use one SIMM at a performance cost (first 32 bits must be read and latched, then second 32 bits read and all 64 bits presented to the processor). Sounds like you have one of these machines.

That being the case, the whole machine was probably built down to a budget so overclocking may not prove easy. If your motherboard supports it you could try 2.5*60 (150MHz) as lots of early 133s will run at 150, however I believe later 133s where subject to Intel's first attempt at multiplier locking.

[sjs74]

Here's my recommendation for you, throw in two 16 meg simms and your performance will probably triple at least. Also, I wouldn't overclock it if you are giving it to somebody as a gift. The reason is that if you ever start having problems with it you won't want to have to try and fix it over the phone. When giving a computer away safer is better, you won't want to ever deal with it again.