Mixing 2GB DDR2 PC-6400 & 512MB PC-5300 in a laptop

rubadub

I am working on a dell inspirion 1525 laptop with 2x512MB PC-5300 667Mhz sticks in it. I have got a single 2GB PC-6400 800Mhz on the way for it.

I know mixing the ram means it runs at the slowest. So is there a point where you are better off not putting in the small & slow stick. e.g. is there a forumla like

2GBx800Mhz=1600"units"

if both are in and slowed to 667
2.5GBx667Mhz=1667.5"units"

I also expect it might end up running smoother with just the 1? especially as they are mismatched in size & speed.

And if there is little difference we could stick the 2x512mb in a friends laptop, not that its expensive.

EDIT: found this page asking similar
http://www.tomshardware.co.uk/forum/287028-30-mixing-speeds

If you're curious about your 'mix' then test with Super PI, next pull the 512MB stick and retest, next pull the 2GB and test with 2X512MB. Compare the results. Anything else is a subjective 'guessing game.'

My assumption is the results will be small.
Super PI - http://virgilioborges.com.br/hyperpi/

Monotype

It won't run in dual channel for starters, which means your bandwidth is halved... although this often doesn't make much difference until you use memory heavy applications.

So long as the computer supports it, with older systems like that, more RAM is better, assuming that the system supports it. Also, some motherboards/laptops just don't like different RAM modules mixed, so you don't have a choice.

As you mentioned, if you want to run it at the higher speed, you probably won't notice much difference between 2.5GB and 2GB, but it is 20% faster than if you used both.
If there's the options in the BIOS menu, you might be able to set them at whatever speed. A lot of RAM is the same thing, just re-branded for different speeds. I'd have my doubts it'll have many options if it's a Dell laptop though.

marco_polo

rubadub wrote: »

I am working on a dell inspirion 1525 laptop with 2x512MB PC-5300 667Mhz sticks in it. I have got a single 2GB PC-6400 800Mhz on the way for it.

I know mixing the ram means it runs at the slowest. So is there a point where you are better off not putting in the small & slow stick. e.g. is there a forumla like

2GBx800Mhz=1600"units"

if both are in and slowed to 667
2.5GBx667Mhz=1667.5"units"

I also expect it might end up running smoother with just the 1? especially as they are mismatched in size & speed.

And if there is little difference we could stick the 2x512mb in a friends laptop, not that its expensive.

EDIT: found this page asking similar
http://www.tomshardware.co.uk/forum/287028-30-mixing-speeds

In terms of performance the capacity doesn't really come into it. Its all about the maximum transfer rate (Until you start to run out of space at least). How fast you can get things into memory, and how much you can fit in there are really two completely separate things.

Max transfer rate = (clock speed) X (number of bits) / 8
800 X 64 / 8 = 6400 Mb/s
667 X 64 / 8 = 5300 Mb/s

Although it doesn't apply to either of your scenarios, the reason dual channel with matching dimms is twice as fast, is because the memory controller can transfer twice as many bits per second.

800 X 128 / 8 = 13200 Mb/s
667 X 128 / 8 = 10672 Mb/s

Theses two images are a very good way to visualise what is going on. In your case with two mixed dims it would be more like the first image (Except in your case with mixed capacities).

http://www.hardwaresecrets.com/imageview.php?image=40136
http://www.hardwaresecrets.com/imageview.php?image=40137

In fact the entire article is worth reading.
http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-the-Dual-Triple-and-Quad-Channel-Memory-Architectures/133/1

In practice though what is more important than clockspeeds or maximum transfer rates, which tend to have only a few % of impact on overall system performance , is having enough RAM to cover your usage, as the real performance killer is when you start running low on RAM and pagefile usage goes up drastically.

For example if your RAM usage is 2.1 GB and you have given away that 512 GB stick, the disk thrashing as data gets copied between the HDD and memory will make you wish you hadn't.

TLDR, if you never go close to or over 2GB the single stick would perform slightly better, but if you go between 2-2.5GB it will perform orders of magnitudes worse.

rubadub

Cheers guys, makes sense. I will stick with the single 2GB. We checked RAM usage in task manager and it was almost constantly above the 1GB, I don't think it every peaked over 2GB. Its running vista and just used for basic internet & music etc, no heavy programs.

The HD certainly was cranking away using the page file, and the inspiron 1525 is known as having a nasty sounding fan which was kicking in all the time. I swopped out the HD and installed Xubuntu on it and the difference was clear, the fan rarely came on at all.

This comparison benchmarking found little difference between dual & single channel, though running on a better PC.
http://www.tomshardware.com/reviews/PARALLEL-PROCESSING,1705-11.html