DDR2 - Why Consider It?
Compared to DDR, DDR2 offers extraordinary performance, reduces power consumption, maximizes DRAM throughput, improves signal integrity, and optimizes flexibility. Some of the measurable differences are highlighted in the comparison chart below.
| Feature/Option | DDR | DDR2 | DDR2 Advantage |
|---|---|---|---|
| Package | 66-pin TSOP 54-, 60-ball FBGA |
60-, 84-ball FBGA 63-ball FBGA DDP |
Enables better electrical performance and speed, dual die package enables higher densities |
| Voltage (core and I/O) Low volt |
2.5V-2.6V N/A |
1.8V 1.55V |
Reduces memory system power demand DDR2 offers a low voltage solution |
| Densities | 256Mb to 1Gb | 256Mb to 4Gb | High-density components enable large memory subsystems with fewer chip counts |
| Internal banks | 4 | 4 and 8 | 1Gb and higher density DDR2 devices have 8 banks for better performance |
| Prefetch (MIN WRITE burst) | 2 | 4 | Enables faster clock rates |
| Data rate (MT/s per pin) | 333 400 667 800 |
533 667 800 1066 |
Migration to higher data bandwidth |
| READ latency Additive latency (posted CAS) |
2, 2.5, 3 CLK N/A |
CL + AL CL=3, 4, 5, 6, 7 AL options 0, 1, 2, 3, 4, 5, 6 |
Eliminating one-half clock settings helps speed internal DRAM logic and simplify timing Mainly used in server applications to improve command bus efficiency |
| WRITE latency | 1 clock | READ latency - 1 | Improves command bus efficiency |
| DQ bus termination | Motherboard parallel to Vtt | DRAM on-die termination (ODT), optional on-motherboard termination | ODT for both memory and controller improves signaling, lowers power, and reduces system costs |
| Data strobes | Single-ended | Differential or single-ended | Improves system timing margin by reducing strobe crosstalk |
| Modules | 184-pin DIMM
|
240-pin SODIMM
|
Improved layout, more form factors, and power delivery design |