DDR3 stands for double data rate three and is a RAM technology used for high-speed storage of working data of a computer or other digital electronic device. DDR3 is part of the SDRAM (Synchronous Dynamic Random Access Memory) family of technologies and is one of many DRAM (Dynamic Random Access Memory) implementations. DDR3 SDRAM is an improvement over its predecessor, DDR2.
The main advantage of DDR3 is its ability to transfer data for I/O at up to 8 times the speed of its memory cells, which provides faster bus speeds and higher peak bandwidth than earlier DRAM technologies. However, there is no corresponding decrease in latency, which is therefore proportionally higher. In addition, the DDR3 standard allows the use of chips with capacities from 512MB to 8GB, effectively providing a maximum memory module size of 16GB.
Comparison table
DDR2 vs DDR3 comparison table
| DDR2 | DDR3 | |
|---|---|---|
| current rating is 3.67/5 (291 ratings) | current rating is 3.99/5 (196 ratings) | |
| voltage | 1.8 Volts (standard); 1.9V (high performance) | 1.5 volts (standard); 1.65 Volts (high performance); 1.35V (low voltage) |
| Speed | 400 MHz, 533 MHz, 667 MHz, 800 MHz, 1066 MT/s | 800 Mhz, 1066 Mhz, 1333 Mhz, 1600 Mhz, and 1866 Mhz |
| Modules | 240-pin unbuffered registered DIMM; 200-pin SODIMM; 214-pin MicroDIMM | 240-pin DIMM (same size as DDR2 but electrically incompatible with DDR2 DIMMs and has a different key notch location). DDR3 SO-DIMMs have 204 pins. |
| Prefetch buffer | 4n | 8n |
| Bus clock | 200-533 MHz | 400-1066 MHz |
| Internal speed | 100-266 MHz | 100-266 MHz |
| Transmission speed | 0.40-1.06 GT/s (gigatransfers per second) | 0.80-2.13 GT/s (gigatransfers per second) |
| Channel bandwidth | 3.20-8.50 Gbps | 6.40-17.0 Gbps |
Advantages of DDR3 over DDR2
- Higher bandwidth up to 1600 MHz: The main advantage of DDR3 is the higher bandwidth provided by the 8-bit DDR3 prefetch as opposed to the 4-bit DDR2 prefetch or 2-bit DDR buffer. DDR3 modules can transmit data at an effective clock rate of 800-1600 MHz using both the rising and falling edges of the 400-800 MHz I/O clock. In comparison, the current effective data rate range of DDR2 is 400-800 MHz when using a 200-400 MHz I/O clock, and the DDR range is 200-400 MHz when using a 100-200 MHz I/O clock.
- Higher performance with lower power consumption (longer battery life in notebooks): DDR3 memory promises a 30% reduction in power consumption over current commercial DDR2 modules due to the 1.5V DDR3 supply voltage versus 1.8V DDR2 or 2.5V.
- Advanced low power features
- Improved thermal design (cooler)
Disadvantages of DDR3 vs. DDR2
- DDR3 usually has a high CAS latency: While typical latencies for JEDEC DDR2 devices were 5-5-5-15, standard latencies for newer JEDEC DDR3 devices are 7-7-7-20 for DDR3-1066 and 7-7-7-24 for DDR3-1333. DDR3 latencies are numerically higher because the clock cycles by which they are measured are shorter; the actual time interval is usually equal to or less than the DDR2 delays. Moreover, although these are standards, manufacturing processes improve over time. Ultimately, DDR3 modules will probably be able to run at lower latencies than JEDEC specifications. You can find DDR2 memory that is faster than the standard 5-5-5-15 speeds, but it will take time for DDR3 to fall below JEDEC latencies.
Videos explaining the differences
Physical differences
The following images show what the DDR2 and DDR3 DIMMs look like.
Diagram of the physical structure of DIMM DDR2, DDR3, and DDR4 modules.
DDR2 and DDR3 RAM modules
DDR2 vs. DDR3
Video cards need fast data transfer between frame buffers. So the higher DDR3 bandwidth is useful.
