PowerMac RAM - ECC and NonECC - Can you Mix them?

[JasonGough]

I'm waiting on my new Dualcore 2.3 PM now, its coming with 1 gig of non ECC RAM in it.

I'm going to buy another gig of RAM from Crucial, and i noticed that they only charge £10 more for the ECC versoin of their 1 gig kits.

Since the Apple RAM in my Mac will be Non ECC, i was wondering, can i / should i mix them, or keep them the same?

If it is possible to mix them, is there a way to get it so that the Crucial ECC RAM is the 'primary' RAM, so that it is the 1st pair of RAM chips to use if i need less than 1 gig of RAM? Or will OSX spread the RAM accross all the chips regarless of total useage?

Any help would be great!

 

[robbieduncan]

I would be surprised if you can mix them. If you can let us know!

 

[grapes911]

You generally cannot mix them in the PC world. I don't think Macs can do it either.

 

[robbieduncan]

The manual for these PMs is here. As I am on my work PC and it's having some sort of PDF issue at the moment I can't tell you if this document helps or not (sorry).

 

[robbieduncan]

PC/Acrobat tissy fixed. Page 51 of the manual says

"Error-correcting code (ECC) or no error-correcting code (NECC) modules. Do not mix ECC and NECC memory modules within a pair."

That seems to imply that mixing ECC and NECC pairs is OK?

 

[matt1190]

Not to jack the thread but what's the difference between the two??

 

[ipacmm]

Not to jack the thread but what's the difference between the two??

ECC RAM (error correcting code) is normally used on a server motherboard for more reliability and costs more, the extra 8 Bits is used to correct the data passing through. Your motherboard probably cannot use ECC RAM and if it able to use ECC RAM it cannot be combined with NON ECC RAM. ECC is parity RAM, Non-ECC RAM is Non-parity RAM. Most types of RAM come in either NON ECC or ECC.

 

[CanadaRAM]

If you mix pairs of ECC and nonECC, the ECC function will be disabled for all RAM.

The only time you want ECC RAM is if you are running a server or a high end engineering/media workstation, where absolute accuracy is more important than speed. ECC RAM moves data as 9 bits for every 8 bits, the 9th bit is used as a check that the other 8 are all accurately read and written. This takes a bit of extra time, so ECC RAM is slower than non-ECC. The rate of memory chip errors is vanishingly small, so it is of practical use only to high-use, mission critical machines.

 

[robbieduncan]

Not to jack the thread but what's the difference between the two??

ECC has additional an additional bit per byte (or is it two bits, anyway) that allows for the memory modules to automatically detect errors in memory. Non-ECC doesn't.

Basically everytime your machine writes to RAM there is a teeny tiny chance that one of the bits will write wrong. This allows for detection and correction of that.

Due to the addtional storage and logic these ECC memory tends to be more expensive.

 

[JasonGough]

ok, so sounds like there is no point in the ECC crucial ram then. Apple realy take the piss here, not just that their RAM is well expensive anyway, but they charge £150 for a gig of ECC RAM!! Crucial charge £80. Thats well out of order.

Thanx very much for your help everyone, think i'll just save a tenner and get the Non ECC RAM