Is there a difference between 2x2GB and 1x4GB RAM?

Possible Duplicate:
Is it better to have 4x2GB or 2x4GB of RAM?

Given the choice between either 2x2GB or a single 4GB RAM module with all other advertised aspects being equal (same price, same CAS latency, same frequency, etc.) which one is preferred?

It seems to me that buying the single stick gives greater opportunity to upgrade (especially with a motherboard with only 2 slots anyway), however people recommend matching pairs, and I guess picking up a matching stick at a later date is somewhat unlikely.

It also seems to make sense that two sticks would give twice the performance of a single stick. However does this actually happen? The motherboard in question is dual channel (currently running 2x1GB) which I guess makes a difference here?

Solution 1:

Reasons to go for two:

Main reason considered is for the extra throughput of the dual channel (accessing both RAM modules at once). The actual improvement from this is a subject of some debate though e.g. http://www.tomshardware.com/reviews/PARALLEL-PROCESSING,1705-15.html

As expected, the performance difference between single channel and dual channel DDR2-800 memory using an up-to-date Core 2 Duo system Compare Prices on Core 2 Duo Processors is little to nil, depending on the benchmark - most tests show differences, but they are really small. For games and enthusiast PCs, we recommend sticking to high-performance dual channel RAM, because the memory is one of those components that you want to perform best for a smooth experience. For regular applications, though, it doesn’t really matter much whether you run single or dual channel. Two 1 GB DIMMs typically are cheaper than a single 2 GB module, but a single DIMM will reduce your power consumption by several watts (which might just be more interesting than it is important).

Cost is also potentially a factor as two smaller DIMMs are often cheaper than the single large DIMM (as mentioned in the quote above)

Reasons against are those of extra heat and system load; and also the upgradability point that you raised initially.

There's debate on similar lines in the following SU question: Is it better to have four times 2 GB or two times 4 GB of RAM?

Solution 2:

Two factors playing here:

• 2*2G gets some benefit from dual channel operation but
• 1*4G leaves more memory slots free for future upgrades.

Per my experience having enough memory makes machine always feel faster than having dual channel operation. For that reason I personally prefer larger stick over smaller ones; You lose some small percent of theoretical bandwidth now, and win significantly later on, by being able to populate the free slots without throwing anything away.

With possible exception of gaming with AMD APUs, most current CPUs do not benefit overtly much from additional memory bandwidth, they mostly care about latency, which explains why the option 2 might be better right now. Look at the speed effects on Intel CPUs and AMD CPUs. As you can see, the difference between 800 and 1600MHz sticks is in most cases unnoticeable, some 16-17% at worst. This tells that the bottleneck for the application is something other than bandwidth.