Thursday, September 27, 2001
Basics of DDR Memory
DDR (double data rate) SDRAM memory technology is a revolutionary new technology derived from the mature SDRAM technology.
The secrets behind DDR memory''s high performance architecture are its capability to perform two data read/write operations in one clock cycle – therefore providing twice the throughput of SDRAM. If you have not read our previous article regarding DDR Memory Click Here to find out how to identify a DDR Memory module.
How many type of DDR memory are there?
DDR memory currently supports memory bus speeds of either 100 or 133MHz, with newer and faster memory bus speed such as 166 and 200Mhz still under review by the JEDEC committee. Recently while researching online for memory prices update , I chance upon an unofficial new addition to the DDR family – called the PC2400 DDR DIMM memory.
Corsair Memory an industry leader in high density DRAM DIMM Memory Modules have aggressively announced that it is now offering Extended Memory Speed ("XMS") Double Data Rate DIMMs. These modules support a memory clock speed of 150 MHz, which yields a memory data rate of 300 MHz, or 2.4 gigabytes per second.See picture of Corsair DDR Module.Check Corsair press release
Infact there is no such thing as a PC2400 standard, currently DDR SDRAM comes in three flavours, PC1600, PC2100 , PC2700 and now adding the fourth flavour PC2400.
PC2100 SDRAM are used in systems running with a 133 MHz (266 MHz) front side bus, and PC1600 SDRAM are used in systems with a 100 MHz (200 MHz) front side bus.
What is PC2400 exactly?
After researching JEDEC Web-site, I could not find any information on PC2400 and for those readers who are curious, this is how PC2400 should be interpreted.
PC2400 describes the memory''s data transfer rate of 2400 MB/sec (2.4 GB/sec) on a 64-bit bus rather than its MHz speed, the current PC2100 memory transfer rate are 2100 MB/Sec (2.1 GB/sec), therefore the PC2400 name sound reasonable.
PC2400 is Non-Jedec Standard
PC2400 is not approved or endosed by JEDEC infact its a clever marketing campaign developed by enterprising memory resellers to spur demand for memory sales during this slow season.
The JEDEC committee are currently finalising the next standard for the PC2700 DDR Memory, which will allow you to run a healthy 166 MHz FSB (333 MHz) effectively. For more information on the Jedec standard Click Here for more information.
What PC2400 offers are its guarantee that the memory module will run beyond its published specification and PC2400 basically refers to the fact that these sticks will allow you to run the your system at 150 MHz FSB (300 MHz effectively).
PC2400 DDR is designed for use with CPUs which run on a 133MHz FSB (266MHz DDR) which is known to run stable when the CPU Front-Side-Bus (FSB) is overclocked to a 150MHz (300MHz DDR) FSB. The latest VIA P4X266 DDR chipset with the Intel Pentium 4 CPU can be overclocked to 160Mhz FSB(320Mhz effectively) using 1 Mhz increment.
Many advance PC users such as serious gamers always try to stretched their system performance beyond manufacturer ‘s recommended specification just to gain a notch or two on system performance. However this technique are very risky and we do not recommend any novice user to try it unless you are familiar with over-clocking techniques.
PC2400 DDR memory must use DDR-266 “A Grade” memory chips, which are usually rated for CAS2 latency operation at 266MHz. These DDR modules are usually programmed for CAS 2.5-3-3 operation at 300MHz via the serial presence detect (SPD) EEPROM.Click here for Micron Data sheet
The following picture shows an example of how a PC2400 DDR memory module could be package with a Heat-Spreader similar to Rambus modules.Running at 300Mhz - the DDR SDRAM chips gets heat up very quickly and may caused the memory be unstable - therefore a Heat-Spreader may be neccessary to dissipate heat quickly and to protect the module from overheating. You will find many other PC2400 memory may be sold without a heat-spreader.
Where to buy PC2400 modules?
The price for PC2400 rated memory module are slightly more expensive than PC2100 memory module,Muskin sells the 256MB PC2400 module for U$62.
Check out this few sites for current prices:
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Copyright 2001 CST Inc
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