Wednesday, July 16, 2008

DDR vs. DDR2

Manufacturer: Corsair
Supplied by: Corsair

by Brian Tiller (8/26/2004)


Now that DDR2 is out, motherboard manufacturers have gotten geared up for its appearance. Is now the time to go for the gusto and upgrade? Hopefully this article will help to shed some light on that question as we pit the new against the old.

Now, I'm not saying that the days of DDR are over, but we've pretty much seen the limits of what DDR is capable of. DDR2 is the next logical progression for memory standards and speeds. DDR2 incorporates several new designs and specifications which play a part in it's increased speed.

On-Die Termination
On-Die Termination is what it sounds like. With DDR, excess signal noise was eliminated by transistors built into the motherboard, but DDR2 has the terminating transistors built into each memory chip.

Posted CAS and Additive Latency
These two, prevent data collisions within the memory while still able to transfer more read/write instructions per clock cycle.

Off Chip Driver Calibration
Increases signal integrity

DDR uses a 2-bit prefetch while DDR2 now uses a 4-bit prefetch.

No, not the cardboard and plastic that the memory comes shipped in, but the packaging of the memory chips themselves. Using a Fine Ball Grid Array (FBGA), DDR2 can be made smaller than DDR which uses Thin Small Outline Package (TSOP).

Below is a small chart, courtesy of Corsair, which outlines the major differences of the two types of memory.

Data Bus 64 bits 64bits
Data Rate 200/266/333/400 Mbps 400/533/667 Mbps
Bus Frequency 100/133/166/200 MHz 200/266/333 MHz
DRAM Frequency 100/133/166/200 MHz 100/133/166 MHz
Package Type TSOP-II FBGA
Densities 256MB 512MB 1GB 256MB 512MB 1GB
Voltage 2.5V 1.8V
Prefetch Size 2 bits 4 bits
Burst Length 2/4/8 4/8
CAS Latency 1.5, 2, 2.5 3+, 4, 5
Write Latency 1T Read Latency -1

From this chart you can tell that DDR2 effectively picks up where DDR1 leaves off. It's data rate begins at 400 and scales upward to 667 currently. Another thing to take notice of are the latencies; they are double those of DDR. Apparently, they are sacrificed for the higher speed, and it should be interesting to see what kind of a trade off it is.

Voltage requirements for DDR2 are greatly reduced from that of DDR. Down to 1.8 volts; this translates into a lot less power needed to read and write for the memory.

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