Computer memory.

pre65 · Post by **pre65** » Sat Jan 10, 2015 12:23 pm

After trawling Ebay for some computer memory I've learned a bit about all the different types.

One question though, if I require 1066 MHz, would 1333 MHz do as a replacement ? (not necessarily expecting better performance)

jack · Post by **jack** » Sat Jan 10, 2015 12:58 pm

All else being equal (right sort of memory etc.), thdn yes. Speeds are backwards compatible.

chris661 · Post by **chris661** » Sat Jan 10, 2015 1:50 pm

I suspect they're also forwards-compatible. ie, you could use the 1066MHz in a slot that'll support 1333MHz, and just get slightly lower speeds.

Chris

jack · Post by **jack** » Sat Jan 10, 2015 2:33 pm

chris661 wrote:I suspect they're also forwards-compatible. ie, you could use the 1066MHz in a slot that'll support 1333MHz, and just get slightly lower speeds.

True, but you don't want to do that.

The memory bus will de-rate to suit the slowest memory on it, i.e. if you put slower memory than is already in place into a computer to "upgrade" it, ALL the memory will then run at the slowest rate.

Good article on what the numbers mean: http://www.hardwaresecrets.com/article/ ... timings/26

pre65 · Post by **pre65** » Mon Jan 12, 2015 11:06 am

Has solid state memory got a limited life ?

In particular DDR3.

jack · Post by **jack** » Mon Jan 12, 2015 12:19 pm

pre65 wrote:Has solid state memory got a limited life ?

In particular DDR3.

No

You might be thinking of static rather than dynamic memory, i.e. FLASH memory, which does have a limited number of write cycles (depending on the type of flash - there are several different physical architectures). All sorts of techniques are used to extend the life of flash memory (as used in USB sticks etc.), such as "wear levelling" and the clever use of hot-spot analysis with associated high-cycle (and more expensive) caches.

pre65 · Post by **pre65** » Fri Jan 16, 2015 10:04 am

Isn't memory complicated.

I got some DDR3 off Ebay, but it turned out to be server memory, no good for a PC.

The seller has agreed to take it back and refund the spondoolicks.

jack · Post by **jack** » Fri Jan 16, 2015 10:50 am

The main difference between "server" and "pc" memory is that server memory has extra bits on it that implement "ECC" - Error Correcting Code - this allows the memory to automatically detect multiple bit errors and to actually correct single bit errors on-the-fly without processor intervention. This is NOT the same as "Parity" memory which PCs use - a parity bit simply allows you to detect, but not correct, single bit errors and doesn't help with multi-bit errors.

ECC memory is more complex and not as widely used as non-ECC memory, so generally costs a LOT more.

Servers also use "Buffered" memory - this is an extra complication that is used in servers to further guarantee memory speed when the server has very large amounts of RAM - servers can have over 512 Gb of RAM, especially if they are running large databases.

So, the type of DDR3 you will be needing is non-ECC and UNBUFFERED.

pre65 · Post by **pre65** » Sat Jan 17, 2015 12:35 pm

Although Dell specify 1066 MHz memory, the two 1GB modules in mine were, in fact, 1333 MHz.

So, now the 2GB modules (also 1333 MHz) have arrived, and fitted.

As I understand things, Windows 7 32bit can only use 3.5GB of memory max, but with two 2GB modules things certainly run a bit quicker.

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