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drkohler on 12 March 2014
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mine said:

Yes. Because it is a special type of RAM TAILORED for GPUs - big latency but you can read and write at once.

1. DDR RAM is made for CPUs - low latency and you can read OR write at once.

Now lets investigate further why GDDR only is a bad idea on a CPU like AMDs Jaguar

2. But as already written - if this would be the case ALL high end servers (POWER, Sparc) would ship with GDDR instead of DDR .

3. The opposite is the truth: DDR is better for CPUs and GDDR is best for GPUs. And to "glue" both together it's best to use something ultra-fast like EDRAM or ESRAM.

You are somewhat confused about the technologies you try to explain so you pretty much get everything wrong. Just a few notes:
1. ddr ram is made for everything that needs memory. No memory in the world can "read and write at once". You always have to tell your memory what cell(s) you want to read OR write. If you really wanted low latency, you'd go with sram, else you take other memory types.

ddr ram chip: cheap (per MB), high capacity hence small, fast (low to medium latencies), low bandwidth, relatively simple to address, difficult mb layout

sram chip: expensive (per MB), low capacity hence large, very fast (very low latencies), high bandwidth, simple to address, difficult mb layout

gddr ram chip: soon cheap? (per MB), medium capacity hence large, fast (low to high latencies depending on program mode), high bandwidth, complex to address, simple mb layout.

gddr memory chips have higher latencies because they need more clock cycles to "setup and ready" the data. However, gddr operates on two forward clocks which are significantly higher than ddr clocks, hence the latencies hardly differ in the end.

2. Servers operate somewhere away from you. Memory latency is completely irrelevant compared to the time it takes to send/receive data. Since servers need a lot of preferrably cheap memory (and densely packed), all servers obviously use ddr.

3.  Up to now, ddr and gddr have never been "glued". The pc has ddr on the main board, gddr on the graphics card, because these memories were logically separated from one another. There is no "glue" intended to use both types together. On full hsa systems, expect to see gddr systems only in the future (for better systems), ddr only (for average systems).