Definition of 'Matching Memory Modules'?

macman

I've just done a RAM upgrade on an Acer PC. Fitted 2 x 512MB DDR3200 modules in the 2 free slots. According to the Crucial site, this mobo (Acer J89M) requires matching modules in pairs.
But upon inspection, the existing RAM consisted of 1x512MB and 1x256MB. I'm guessing that it originally had 256MB, and someone previously added 512MB. In theory, this should not have worked. Yet the PC is and was perfectly stable.
So why did it work? Does the actual module size not have to be matched?

weegie.geek

They recommend you use identical modules so it can work as efficiently as possible, in dual channel mode. In reality, there's not much of a performance boost using dual channel mode, so I wouldn't worry about it.

macman

OK, but on Crucial there is a clear distinction shown between mobo's that they say will run faster with matched modules, and ones which they say must have matched modules. This was clearly shown as being in the latter category.

Marksweb

Yeah to run the system with proper dual channel ram, you'd need the same speed & same size on each dimm in each channel.

If you have it like you do now, its probably running single channels.

Hammyman

Running in dual channel mode, memory throughput is about 80% faster than in single channel mode.

Richie-from-the-Boro

macman wrote: »

I've just done a RAM upgrade on an Acer PC. Fitted 2 x 512MB DDR3200 modules in the 2 free slots. According to the Crucial site, this mobo (Acer J89M) requires matching modules in pairs.
But upon inspection, the existing RAM consisted of 1x512MB and 1x256MB. I'm guessing that it originally had 256MB, and someone previously added 512MB. In theory, this should not have worked. Yet the PC is and was perfectly stable.
So why did it work? Does the actual module size not have to be matched?

- dual is better [ ganged ] than single
- same same is better than different size / slugs / speed / sides / voltage

Your MOBO has independent slots so you can have differing capacities so long as they each / all run at less than 2.5V. What's done is done, you don't say what the speed [ DDR400 for example ] of the original two -and the new two bars were ?

macman

All 4 RAM modules are DDR 3200.
So the consensus is that it will run (which it obviously is), but there's a speed hit in doing it this way.

Richie-from-the-Boro

macman wrote: »

All 4 RAM modules are DDR 3200.
So the consensus is that it will run (which it obviously is), but there's a speed hit in doing it this way.

Yes .. .. .. there was / is a compromise to be made on your part in order for you to be able to re-use your existing [ old bars of ] memory. You were fortunate that your MOBO allowed the 4 bars to be independently addressed. Don't feel too bad, your investment is not wasted you have a working machine and didn't have to :

- replace all four bars
- or worse still a new MOBO / memory requirement

macman

It's not my PC, if it was I'd have the full 2GB installed!

[Deleted User]

macman wrote: »

All 4 RAM modules are DDR 3200.
So the consensus is that it will run (which it obviously is), but there's a speed hit in doing it this way.

You're not going to get peak performance because:


[*] It's not Dual Channel

[*] The timings are probably different

[*] Extra stress on the Memory Controller

It's unlikely that the above factors will make any perceivable difference though.