Technology

The first PC motherboards with support for RDRAM debuted in 1999. They supported PC800 RDRAM, which operated at 400 MHz but presented data on both rise and fall of clock cycle resulting in effectively 800 MHz, and delivered 1600 MB/s of bandwidth over a 16-bit bus using a 184-pin RIMM form factor. This was significantly faster than the previous standard, PC133 SDRAM, which operated at 133 MHz and delivered 1066 MB/s of bandwidth over a 64-bit bus using a 168-pin DIMM form factor.

Some downsides of RDRAM technology, however, included significantly increased latency, heat output, manufacturing complexity, and cost. PC800 RDRAM operated with a latency of 45 ns, compared to only 7.5 ns for PC133 SDRAM. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heatsinks on all RIMM devices. RDRAM also includes a memory controller on each memory chip, significantly increasing manufacturing complexity compared to SDRAM, which used a single memory controller located on the northbridge chipset. RDRAM was also two to three times the price of PC133 SDRAM due to manufacturing costs, license fees and other market factors. DDR SDRAM, introduced in 2000, operated at an effective clockspeed of 266 MHz and delivered 2100 MB/s over a 64-bit bus using a 184-pin DIMM form factor.