Double Data Rate 2 (DDR2) replaced Double Data Rate (DDR) SDRAM in much the same way that DDR has replaced SDR memory.
DDR2 advantages over DDR:
(1) Lower voltage requirement (in most cases, unless overclocking). DDR requires 2.5 volts while DDR2 only requires 1.8 volts. This gives an edge especially in mobile computing where battery life is important, and allows the chipset to run cooler at high frequency.
(2) Double bandwidth. Instead of two bits transferred through the bus at a time, DDR2 has four bits transferred. Like DDR, this transfer occurs twice each bus clock cycle (compare to SDR once per cycle).
(3) Higher data rate. DDR chips are produced from 200 up to 400 Mhz, while DDR2 chips are produced from 400 Mhz up to 800 Mhz and beyond
DDR2 disadvatages compared to DDR:
(1) Higher latency. Because more data is transferred per cycle, the read latency is increased. There is a larger buffer from the bus to the storage, so more data must be processed before it can be accessed. This eventually is overcome by clock speed in the chip. The break even point is considered to be at DDR2-533 speed. At that point and beyond, DDR2 outperforms DDR because of higher bandwidth.
(2) Higher cost.
(3) Not backwards compatible. Older motherboards that were produced for DDR will not be able to use DDR2 SDRAM.
On the physical side, DDR has a 184-pin DIMM interface and DDR2 has 240.
DDR2 runs cooler and has generally slower timings but is a lot faster than DDR in the end. DDR2 is capable of holding more ram on one DIMM.
2.) Does DDR2 do more work per cycle? And Does AMD Support DDR2 Ram?
AMD doesn't support DDR2 as the A64's built-in RAM controllers would have to be upgraded therefore making them incompatible with all the current motherboards out there which really wouldn't be worth AMD and the board manufacturers' time.
* DDr1=184pin DIMM and DDR2=240pin DIMM.
* DDR2 has much higher bandwidth and chip density/# of chips per DIMM, allowing more ram to be effectively used (also the reason why it's best to go for 1-2gb of DDR2) at a higher speed, but at the expense of latency.
* On the other hand, DDR1 runs at lower speeds but much tighter timings
It is difficult to differentiate a DDR2 from a DDR motherboard just by looking at it. Inserting a DDR2 DIMM into a DDR motherboard could damage the module, the motherboard, or both. To prevent such damage, the simplest process is to align the memory module and the socket, and visually check that the module “key” aligns perfectly with the socket key. You may have to turn over the memory module as the memory module direction may misalign even compatible socket and module keys.
3. What latencies will standard DDR2 DIMMs support?
JEDEC DDR2 specifications define standard DDR2 CAS Latencies of 3, 4, and 5: