DDR is running at 100Mhz, 133Mhz, 166Mhz, 200Mhz, 233Mhz, or 266Mhz. What makes this separate from the older types of SDRAM (PC100, PC133) is that DDR can transfer memory on both the rise and the fall of a clock cycle. So, essentially, you are getting 200Mhz, 266Mhz, 333Mhz, 400Mhz, 466Mhz, or 533Mhz respectively.
DDR2 is running at 266Mhz, 337Mhz, 375Mhz, 400Mhz, and 450Mhz. So, essentially, you are getting 533Mhz, 675Mhz, 750Mhz, 800Mhz, and 900Mhz respectively.
DDR3 is running at 533Mhz, 666Mhz, and 800Mhz which provides a total speed of 1066Mhz, 1333Mhz, and 1600Mhz.
With the introduction of competing DDR SDRAM memory, the DDR standards groups turned against the standard clock speed naming schemes such as PC100 and PC133 used for the older SDRAM modules, and instead named their parts by the amount of peak bandwidth they could utilize.
For example, a 200 MHz DDR module wasn't called DDR-200, rather was called PC-1600, as the module could operate at 1.6 GB/s. Of course, the follow-ups like PC-2100 (2.1 GB/s), and PC-2700 (2.7 GB/s) followed and gave the impression that DDR SDRAM was faster than current RDRAM memory was. As PC-1600 DDR memory was coming out at roughly the same time PC-800 RDRAM was, people immediately started to think, PC-1600 is faster. However, this is not the case.
So, DDR is most likely going to be known as PC1600 (200Mhz), PC2100 (266Mhz), PC2700 (333Mhz), PC3200 (400Mhz), PC3700 (466Mhz), and PC4200 (533Mhz), whilst DDR2 is going to be known as PC2-4300 (533Mhz), PC2-5400 (675Mhz), PC2-6000 (750Mhz), PC2-6400 (800Mhz), PC2-7200 (900Mhz), PC2-8000 (1000Mhz), or PC2-8500 (1066Mhz) as it correlates to the peak bandwidth potential.
RDRAM or RAMBUS Ram up until a few years ago didn't have the same dual-data-rate features as DDR so was named according to the speed it ran at. So, essentially, PC600 RDRAM runs at 600Mhz, PC800 at 800Mhz, and PC1066 at 1066Mhz. Because each standard RDRAM module has only a single 16-bit channel, the modules have to be installed in pairs to achieve the same bandwidth transfer rates as DDR or DDR-2 ram.
Due to the DDR naming conventions, Rambus had to alter their naming conventions to stay in line as well. In 2002 they introduced RIMM-4200, which is a dual channel PC-1066 memory stick, and can provide peak bandwidth of 4.2 GB/s. There is also a dual channel version of PC-800, which is dubbed RIMM-3200 (3.2 GB/s). So far there have been very few motherboards released to accept this new RIMM technology.
| DDR | Output | FSB | Peak Bandwidth |
| PC1600 | (200Mhz) | 100Mhz | 1.6GB/sec |
| PC2100 | (266Mhz) | 133Mhz | 2.1GB/sec |
| PC2700 | (333Mhz) | 166Mhz | 2.7GB/sec |
| PC3200 | (400Mhz) | 200Mhz | 3.2GB/sec |
| PC3700 | (466Mhz) | 233Mhz | 3.7GB/sec |
| PC4000 | (500Mhz) | 250Mhz | 4.0GB/sec |
| PC4200 | (533Mhz) | 266Mhz | 4.2GB/sec |
| DDR2 | Output | FSB | Peak Bandwidth |
| PC2-3200 | (400Mhz) | 200Mhz | 3.2GB/sec |
| PC2-4300 | (533Mhz) | 266Mhz | 4.3GB/sec |
| PC2-5300 | (667Mhz) | 333Mhz | 5.3GB/sec |
| PC2-5400 | (675Mhz) | 337Mhz | 5.4GB/sec |
| PC2-6000 | (750Mhz) | 375Mhz | 6.0GB/sec |
| PC2-6400 | (800Mhz) | 400Mhz | 6.4GB/sec |
| PC2-7200 | (900Mhz) | 450Mhz | 7.2GB/sec |
| PC2-8000 | (1000Mhz) | 500Mhz | 8.0GB/sec |
| PC2-8500 | (1066Mhz) | 533Mhz | 8.5GB/sec |
| DDR3 | Output | FSB | Peak Bandwidth |
| PC3-8500 | (1066Mhz) | 533Mhz | 8.5GB/sec |
| PC3-10600 | (1333Mhz) | 666Mhz | 10.6GB/sec |
| PC3-11000 | (1375Mhz) | 687Mhz | 11.0GB/sec |
| PC3-12800 | (1600Mhz) | 800Mhz | 12.8GB/sec |
| RDRAM | Output | FSB | Peak Bandwidth |
| PC600 | (600Mhz) | 300Mhz | 2.4GB/sec (per module) |
| PC800 | (800Mhz) | 400Mhz | 3.2GB/sec (per module) |
| PC1066 | (1066Mhz) | 533Mhz | 4.2GB/sec (per module) |
Flash Memory, (including USB Drives, CF Cards, SD Cards, and other types) is often labelled with a speed of 10x, 45x, 133x, etc. Typically this figure is worked out by dividing the maximum write speed in bits per second by 150. The latter figure represents the old standard 1x CD-ROM drive write speed - being 150 bits/sec or 1x. Therefore if a flash card is listed with a speed of 50x, then the maximum write speed in ideal conditions is going to be about 7500 bits per second, or around 7.5 Mbits per second.
To complicate matters further, a new type of flash memory card was introduced, termed "High Capacity". Presently these cards have speed classified as "Class 2" (2 MB/sec minimum data transfer rate), "Class 4" (4 MB/sec minimum data transfer rate), or "Class 6" (6 MB/sec minimum data transfer rate). Already some manufacturers have started introducing their own write speed specification (such as 133x, or 20MB/s) to indicate that their High Capacity cards perform much better than the minimum standard.
<-- Back to FAQ's