Originally Posted by SPE:
CPUs and GPUs have different RAM requirements.
CPUs want RAM with low latency, so they can very quickly access and move small chunks of data around.
GPUs want RAM with high bandwidth, so they can move large chunks of data.
DDR3 is suited for CPUs. It is low latency, but also low bandwidth. It is the defacto RAM found in PCs and servers. You spend $10,000 on a server, and it will use DDR3.
GDDR5 is suited for GPUs. It is high latency, but also high bandwidth. Graphics cars above level entry will use GDDR5 for VRAM.
The Xbox 360 was the pioneer for using GDDR (in its case, GDDR3) for both system and VRAM. The PS4 is following suit. While this might be fine for dedicate gaming machines, for genral purpose computing and CPU intensive work, you want low latency RAM. Which is currently DDR3.
There is a reason the next Xbox has gone for the DDR3 + EDRAM approach. MS have designed the console for more than games. The non gaming apps want DDR3. The EDRAM is there to mitigate the low bandwidth main RAM to a certain degree. Sony seem to have designed the PS4 as a pure bread gaming console. Different priorities resulted in different RAM architectures.
TL;DR you don't want GDDR5 as system RAM in a PC. When DDR5 finally comes to market, it might have best of both worlds. Low latency for CPUs and high bandwidth for GPUs. Only then would you want it as system RAM.
Originally Posted by Iced_Eagle:
Great explanation. However, I believe you meant to say "DDR4" instead of "DDR5" in your tl;dr. DDR4 just recently got wrapped up as a spec. Work hasn't begun on DDR5.
Some other things that I think are important to note:
1) The 3 and the 5 are the version numbers, but for separate things. DDR5 is not a thing yet (they're still working on DDR4 which should start releasing this year or next). It's very important that you have the "G" on there (which stands for graphics). It pains me when people see GDDR5 and DDR3 and think one is the obviously superior version. They are two separate products (imagine if the X360 was named Xbox 2. This is similar to someone saying PS3 > XB2, even though they're two separate product lines).
2) GDDR5 is actually based on DDR3 (as was GDDR4). They're basically two sides of the same coin. DDR3 is focused on low-latency, but with the tradeoff of lower-bandwidth, and GDDR5 has higher bandwidth, at the cost of higher-latency.
These should become mandatory reading fro those people who don't know how computers work.
