by April 5, 2004 0 comments



With all the changes happening in hardware, it’s essential for the memory to keep pace, and the answer to these changes today seems to be DDR II (Double Data Rate Memory), which, like the name suggests is the successor to DDR memory.

The new memory has some distinct advantages over its predecessor, such as lower operating voltage, faster throughputs and a better roadmap to scale performance in the future.

Already players such as Corsair have announced their DDR II memory products, which means we should see some action in this space this year.

Snapshot
Applies to PCs
Usp Higher throughput
Links www.lostcircuits.com
www.theddrzone.com

To explain how DDR works, we’ll first explain the basic elements of a memory module. A memory module is made of three elements, the core, the I/O logic and the power supply.

In ordinary SDRAM (Synchronic Dynamic RAM), the I/O logic is able to fetch a single bit from the core per clock cycle.

Here, both the core and I/O logic work on the same clock frequency, so it’s just a matter of synchronizing the data transfer from one unit to the other. In DDR, the efficiency of operation is improved with the same clock frequencies. So, the I/O logic fetches two bits of data from the core instead of one. This literally doubles the throughput of the memory. This also means that now there are two data lines instead of one from the core. DDR II on the other hand, doubles the I/O clock frequency, and fetches four bits from the core instead of two.

Feature DDR DDR
II
Data
transfer rate
266,
333, 400 MHz
400,
533, 667, 800 MHz
Operating
voltage
2.5
V
1.8V
Density 64MB
to 1 GB
256
MB to 4 GB
Pin
count
180 240
A quick comparison between DDR and DDR II memory

All DDR II modules will use FBGA (Finepitch Ball Grid Array) packaging, which helps reduce the packaging size. This also improves heat dissipation and the performance. Other changes are increased pin count of 240 pins instead of 180 pins in DDR memory. It also operates at a lower voltage of 1.8 V instead of 2.5 V-2.8 V for DDR. The end result is basically augmented memory bandwidth to the system at the expense of latency–number of clock cycles needed to read a bit of information –by effectively using two DRAM (Dynamic RAM) cores instead of one as used by DDR I.

In order to use DDR II, a new motherboard will be required because DDR II is not backward compatible with DDR memory due to a higher pin count and different operating voltage.

DDR II is expected to hit the market sometime this year, both as single and dual configurations. The memory is expected to
reach 667 MHz in 2005 and will be replaced by DDR III in 2007 with a speed between 800 to 1066 MHz.

There are some competing technologies to DDR II as well. One is the QDR (Quad Data Rate Memory), which is not a standard, but a technology developed by Kentron. The other is XDR (eXtreme Data Rate), which is the final name for Rambus ‘Yellowst
one’ technologies. XDR is effectively a hybrid of DDR and Rambus DRAM designed to combine the best elements of both. Finally, there’s also something called QBM (Quad Band Memory), which is a combination of DDR and
QDR.

Sushil Oswal

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