DDR RAM Explained: DDR2 to DDR5, DIMM vs SO-DIMM and ECC for the A+ Exam
DDR stands for Double Data Rate — memory that transfers data on both the rising and falling edge of the clock signal, effectively doubling throughput without doubling the clock. Every generation since has kept that name and increased density, speed, and efficiency. The single most important practical fact: DDR generations are not interchangeable. Each has a different notch position and a different voltage, and they physically will not fit in the wrong slot. That incompatibility is deliberate. The notch in the edge connector sits in a different place for each generation, so you cannot install DDR4 in a DDR3 board even with force — and forcing it damages both. The Generations Type Voltage DIMM pins SO-DIMM pins Typical speeds Era DDR 2.5 V 184 200 200–400 MT/s 2000 DDR2 1.8 V 240 200 400–1066 MT/s 2003 DDR3 1.5 V (1.35 V low-voltage) 240 204 800–2133 MT/s 2007 DDR4 1.2 V 288 260 1600–3200+ MT/s 2014 DDR5 1.1 V 288 262 4800–8400+ MT/s 2020 Two things to notice. Voltage ...