RAM

DDR SDRAM (sometimes called DDR1), finalized by JEDEC in 2000, was the first double-data-rate memory standard -- transferring data on both the rising and falling edge of the clock signal. It used a 184-pin DIMM for desktops and a 200-pin SO-DIMM for laptops, running at 2.5V.

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.

DDR3, standardized in 2007, kept DDR2's 240-pin DIMM count but switched from a rounded to a square notch in a different position, making the two physically incompatible despite the matching pin count. It dropped voltage to 1.5V (1.35V for the low-power DDR3L variant) and raised data rates up to DDR3-2133.

DDR4's spec was finalized in September 2012, though it didn't reach the commercial market until 2014. It moved to a 288-pin DIMM and 260-pin SO-DIMM, dropped voltage to 1.2V, and started at a minimum of 2133 MT/s -- roughly double DDR3's starting point.

DDR5, released by JEDEC in July 2020, splits each memory module into two independent 32-bit subchannels instead of DDR4's single 64-bit channel, and moves voltage regulation onto the module itself via an on-board PMIC rather than relying on the motherboard. Standard data rates start at 4000 MT/s, well above DDR4's ceiling.