DDR2

From Extreme Overclocking

What is DDR2??

The purpose of DDR2 is easier to understand if you have a basic grasp of regular DDR SDRAM. Similar to DDR, DDRII issues the data to the input/output buffer through the broad 64-bit 100mhz internal BUS. However, now the data can flow from the buffer at a faster BUS of 16-bit, 200mhz speed which uses the DDR rule. So then we acheive the frequency of 400mhz. Thus, the 64 bits on the module output are made up of simultaneous transmissions from 4 banks, this memory goes under the name of DDRII-400, like that of regular DDR explaining the data-transfer rate to the memory controller.

The main 'idea' that distinguishes DDRII from normal DDR is due to the frequency of the array of DRAM cells on chip at 100mhz, we have the end result of different module bandwidths. So currently it is 800mb per second for SDRAM, 1600mb per second for DDR, and summarily 3200mb per second for DDRII. Multiplexing allows the module to provide a higher bandwidth even though the cells on chip work at the same frequency or MHZ. However that is not the only difference between DDRII and DDR.

Latencies are another item that distinguishes DDRII from DDR. As stated, the memory cell won't always be available due to the refresh process between CPU and RAM. Even if the cell is in fact available for fetching, it is not possible to get all of its contents right away. Courtesy of Maher-"SDRAM and DDR-SDRAM are designed to work with CAS Latency (CL) of "3" as maximum. This limited the MHz speed of which DDR can achieve to a certain point, or at least within the *safe* or the "voltage standards" of DDR. DDRII architecture is designed to work with upto "5" CL, therefore allowing more preparation time and allowing more MHz to be reached and increasing the bandwidth.."

Take DDR-400 vs. DDRII-400. The bandwidth of both modules is rated the same at 3.2GB per second, but the frequency of the DRAM array is 200mhz with DDR but its 100mhz with DDRII, and as a direct result, total bandwidth can be higher, but the latency timings are tighter or lower with DDR than with DDRII. To go into further detail, DDR-400 usually has CAS timings of 2 or 2.5, and even 3, which ranges from 10 to 15 nanoseconds fetch time. For DDRII-400 we figure out its latency as follows. It will have a latency of 2 at 100mhz clock, which in turn translates to 20 nanoseconds, which means that it will have a CAS latency of 4 since the interface has a higher clock rate. The end result is that instead of 2-2-2-8, the DDRII module will be timed at 4-4-4-12. So, you can see why A64 systems do not utilize DDRII as they rely heavily on tight timings where Intel's rely more so on high bandwidth, and are more tolerable of loose timings, which a DDRII module provides. Basically, it can provide very high bandwidth but at a cost of fetching time, or latencies.

Another difference is the type of chips used on the modules. Typically DDR uses TSOP chips which are good but tend to break up when clocked too high(MHZ). They also have a high resistance, which does not allow for much frequency improvement. DDRII uses a Ball Grid Array or BGA for higher frequencies, and is widely used on graphics cards. It has a lower resistance than TSOP's, is smaller in size, and does not get as hot, largely due to the fact the core can operate efficiently on only 1.8V, as opposed to 2.5-2.8V with DDR. Sounds nice? It can be, but its more expensive to manufacture, thus the higher price of DDRII in the market world. Note however, that these different types of process are not proprietary, as some manufacturers use BGA on DDR as well, so it is interchangeable, but at the higher cost.

Another variable between the two is write latency. DDR typically has a write latency of 1T. DDRII's is dictated by read latency which in turn will equal write latency, minus 1 clock rate. Example, read could be at 6T, so then write would be 5T. It doesnt seem that effective compared to 1T but it is because with DDR, writing takes more time to prepare, but its not so with DDRII, it can get straight to the process.

In conclusion, if your beyond confused, here's a simplified compilation of what we have discussed here in the similarities and differences from DDR to DDRII. It uses a different interface of 240-pins(200 for laptops) as opposed to 184 pins with DDR, so you will not be able to use both in the same board(unless it has DIMM's for both DDR & DDRII), or at the same time. They are both offered in ECC/Non-ECC, registered/Unregistered forms, and are both capable of Dual Channel technology. They utilize different chip types(most of the time), different voltages, DDRII uses less volts and consequently doesnt get as hot, but it costs more to produce, which is why its not widely used for DDR. DDRII can provide much higher bandwidth but at the cost of not having low latencies, and has a much higher frequency at the same clock rates. I have attached a chart that shows the migration of DDR to DDRII courtesy of Crucial's website.

Some manufacturers of DDRII are Viking, Crucial, Mushkin, Infineon, Kingston, Patriot, PQI, Corsair, Wintec, Kingmax, and probably some generic ones you could find on Ebay, but should steer clear of.

More Info

http://www.bytesector.com/data/bs-article.asp?ID=304

http://www.anandtech.com/memory/showdoc.aspx?i=2003

Recommendations

Value/Non-OC'er

Kingston ValueRAM PC2-3200

-CAS 3-4-4-10

-Rated for 1.8V

-No standard heatspreader

-Lifetime MFR. warranty

http://www.newegg.com/Product/Product.asp?Item=N82E16820144166

Mushkin DDR2 PC2-4200

-266MHz 3-3-3-8

-337MHz 4-4-4-12

-354MHz 4-4-4-12

http://www.newegg.com/app/ViewProductDesc.asp?description=20-146-367&depa=1

PQI Power Series Unbuffered (PC2 4200) Dual Channel Kit

-4-4-4-12 standard timings: Capable of 3-3-3-10 timings

-Rated for 1.8V

-Black heatspreaders standard

-Tops out around 614mhz

http://www.newegg.com/Product/Product.asp?Item=N82E16820141225

PNY Optima Unbuffered (PC2 4300)

-Data rate of 533 MHz

-CAS latency 4

-8.6 GB/sec dual channel system bandwidth

-Rated for 1.9V

http://www.newegg.com/Product/Product.asp?Item=N82E16820236102

Performance/Mid-Range/Light OC'ing

OCZ DDR2 PC2-4200 Value Series

-4-4-4-8 standard timings

-Rated for 1.8V

-Lifetime MFR. warranty

http://www.bytewizecomputers.com/products/7/10/676/7026

Kingston 533MHz DDR2 PC2-4200 DIMM

-Capable of high FSB with 1.9V, and timings 4-4-4-10@354mhz.

-266MHz 3-3-2-6

-337MHz 4-4-3-8

-354MHz 4-4-4-10

http://www.bytewizecomputers.com/products/7/10/640/7045

PQI DDR2-533 PC2-4200

-Right on par with the Corsair, but at 1.9V.

-266MHz 3-3-2-6

-337MHz 4-4-4-12

-354MHz 4-4-4-12

http://www.newegg.com/app/ViewProductDesc.asp?description=20-141-191&depa=1

Wintec AMP-X 240 PC2-5400 with Heat Spreader, 1 Rank

-4-4-4-8 standard timings

-Rated for 1.8V

-Available in both non and ECC/Registered versions

http://www.newegg.com/app/ViewProductDesc.asp?description=20-161-644&depa=1

GeIL 1GB PC2-4300 Dual Channel Kit

-266mhz 3-3-3-8 timings on stock volts/FSB

-Rated for 1.8V

-Lifetime MFR. warranty

-*Some reported problems on Fatal1ty AA8XE motherboards*

http://www2.newegg.com/Product/Product.asp?Item=N82E16820144522

High Performance/OC'er

Corsair Twin2X1024-5400C4

-Doesnt like more than 1.9V, nor does it need it.

-266MHz 3-3-2-6

-337MHz 4-4-4-12

-354MHz 4-4-4-12

http://www.bytewizecomputers.com/products/7/10/607/6353

Centon PC-4200 DDRII

-Capable of lower latencies, but at higher 2.0V.

-266MHz 3-2-2-5

-337MHz 3-2-2-5

-354MHz 4-3-3-12

http://www.newegg.com/Product/Product.asp?Item=N82E16820237203

Crucial Ballistix PC2-5300

-Hits FSB of 354mhz at 4-4-4-10, 1.9V

-266MHz 3-3-3-8

-337MHz 4-4-3-10

-354MHz 4-4-4-10

-Review at EOCF

http://www.newegg.com/app/ViewProductDesc.asp?description=20-161-403&depa=1

OCZ Platinum Enhanced Bandwidth Rev.2 LE PC2-4200

-Low Latencies of 3-2-2-8, needs 2.0V

-266MHz 3-2-2-8

-337MHz 3-2-2-8

-354MHz 4-3-2-8

http://www.newegg.com/app/ViewProductDesc.asp?description=20-227-018&depa=1

Corsair XMS2-6400 Dual Channel Kit

-Capable of 800mhz

-5-5-5-12 standard timings

-Rated for 2.5-2.8V

-64MBx8 density

-Optimized for the new Intel Nforce4 SLI boards

Monarch

OCZ Gold 1GB Unbuffered DDR2 800 (PC2 6400)

-5-5-5-10 standard timings

-Rated for 1.9V-2.2V

-Gold mirrored copper heatspreader

-Lifetime warranty

http://www.newegg.com/Product/Product.asp?Item=N82E16820227029