DDR2
RAM · 5 specs
Direct Answer
DDR2, standardized by JEDEC in September 2003, doubled DDR's internal prefetch to 4 bits and dropped operating voltage to 1.8V. Its 240-pin DIMM introduced a new pin count, but its 200-pin SO-DIMM confusingly matches DDR1's pin count -- the two are still incompatible via a different notch position.
Source: JEDEC · Last reviewed Aug 28, 2026
Specs
| JEDEC Standard | September 2003 |
| DIMM Pins | 240 |
| SO-DIMM Pins | 200 (same count as DDR1, different notch position -- not compatible) |
| Nominal Operating Voltage | 1.8 V |
| Data Rate Range | 400–1066 (DDR2-400 to DDR2-1066) MT/s |
A Pin-Count Coincidence That Isn't Compatibility
DDR2 reached JEDEC standardization in September 2003, doubling the internal prefetch buffer to 4 bits (from DDR1's 2 bits) and lowering operating voltage from 2.5V to 1.8V for better power efficiency. Its 240-pin desktop DIMM introduced a new pin count that made desktop incompatibility with DDR1 obvious at a glance.
The laptop SO-DIMM side is a genuine point of confusion: DDR2 SO-DIMM uses 200 pins, the exact same count as DDR1's SO-DIMM -- but the two are not interchangeable. The notch position differs between them, physically preventing a DDR1 module from seating in a DDR2 slot or vice versa, even though counting the pins alone would suggest they should match. Data rates at introduction ranged from DDR2-400 up to a commonly-cited practical maximum around DDR2-1066.