[Binary0101]

I've been wondering, what do you have to consider when you buy RAM? I have been looking at some RAM and they have numbers such as 5-5-5-12 or 4-4-4-15. What do these numbers mean?

What about the bus speeds: some are 800MHZ and some are 667MHZ. Does more mean it's better because i have seen some 667MHZ RAM cost more than 800MHZ.

Finally does it matter what processor you have? (I have an E8400 3GHZ). I have seen some sites say you need ram in the same ratio as the bus speed of your processor.

Any help will be greatly appreciated

[spot]

More is better. The 667/800/1033 whichever has to be at least as high a number as the motherboard will run at for the processor you've chosen. It can be higher or equal but it can't be lower.

The 5-5-5-12 or 4-4-4-15 is the timing delays required for the memory to react. Low is good. Your motherboard BIOS ought to recognize low and speed things up. Reading the motherboard manual is a good idea, maybe yours prefers you to be explicit in these matters.

[Binary0101]

So you're saying that i have to buy RAM which is more or the same bus speed as my mobo?

The max bus speed for the E8400 is 1333MHZ and that's the same for my mobo (asus P5k-E/WIFI)

Does that mean i have to buy RAM which has a bus speed of 1333MHZ? If so I can't seem to find any.

[spot]

Crucial sell it.

2GB kit (1GBx2) Part #: BL2KIT12864BA1608 • DDR3 PC3-12800 • 8-8-8-24 • Unbuffered • NON-ECC • DDR3-1600 • 1.8V • 128Meg x 64
£267.89 inc. VAT*

1GB Part #: CT12864BA1339 • DDR3 PC3-10600 • CL=9 • Unbuffered • NON-ECC • DDR3-1333 • 1.5V • 128Meg x 64
£91.64 inc. VAT*

1GB Part #: BL12864BA1608 • DDR3 PC3-12800 • 8-8-8-24 • Unbuffered • NON-ECC • DDR3-1600 • 1.8V • 128Meg x 64
£133.94 inc. VAT*


I think - though don't quote me - that it's possible to run processor and motherboard slower and use slower memory, but I've never tried it. And to be honest it doesn't sound likely, but perhaps it's in my head because of this exact thing of fastest memory not being available. Someone here'll definitely know. Getting the right memory might be the better option though.

[alex]

DDR2 ram, or Double Data Rate ram reads on the rising and falling edges of the clock cycle, hence the name.

Because of this the speed of ram you purchase isn't a true reflection on it's true mhz speed.

It's industry standard now, because it's double data rate ram, to double up on the mhz rating.

So; DDR2 800mhz ram actually runs at 400mhz true.

DDR3 isn't triple data rate, it's basically just the next revision of ram running at a lower stock voltage and higher, true, mhz ratings.

FSB's, in the case of Intel, are quad pumped. So they're basically measured the same as DDR2 ram. But in this case instead of it being x2 it's now x4.

So; a FSB running at 1333mhz has a true rating of 333mhz.

As long as you purchase ram that has the same or higher true mhz rating than your fsb you'll be fine.

As an example 667mhz DDR2 runs at a true 333mhz (I know it doesn't multiply correctly mathematically but I'm going by the manufacturer's measures here) so it will be fine for a 1333mhz FSB.

If you purchase ram that has a lower true mhz rating than a FSB you'll run into bottlenecks.

As an example DDR2 533mhz ram has a true rating of 266mhz, put that with a 1333mhz FSB (333mhz true) and you'll get your bottlenecks.

The numbers you mention refer to the timings. Simply put this refers to how long the ram takes before streaming it's next packet of data.

Have a read of my overclocking guide for some more info.

Hope this helps.

[spot]

That was worth reading alex, thanks.

[Binary0101]

Thanks Alex, that's really helpful

[Binary0101]

Just one last question: Which attribute is better? The bus speed or the time the RAM takes to transfer the packets data.

The Corsair 2GB (2x1GB) DDR2 800MHZ RAM (5-5-5-12) http://www.ebuyer.com/product/98710 <------ More Bus speed at £32

The Corsair 2GB (2x1GB) DDR2 675MHZ RAM (4-4-4-12)http://www.ebuyer.com/product/98708 <------ Quicker Packet transfer? £36 (less bus speed than above)

[Carbon]

Speed > latency. DDR 800 is the stuff you should be buying.

[alex]

Originally Posted by Binary0101

Just one last question: Which attribute is better? The bus speed or the time the RAM takes to transfer the packets data.

The Corsair 2GB (2x1GB) DDR2 800MHZ RAM (5-5-5-12) http://www.ebuyer.com/product/98710 <------ More Bus speed at £32

The Corsair 2GB (2x1GB) DDR2 675MHZ RAM (4-4-4-12)http://www.ebuyer.com/product/98708 <------ Quicker Packet transfer? £36 (less bus speed than above)

Frankly (within reason) it depends on how the access of data to the memory is controlled. Latency's (again within reason; CL7 is getting stupid) don't really affect an Intel build.