I put my vote on DDR3.
- With DDR3 we finally had some semblance of standardization between manufacturers and vendors.
- The price fixing era of DDR2 had been squashed, oversight and regulation on manufacturers was more strict, and quality improved dramatically.
- Almost out of the gate DDR3 was pushing 2000MT/s (with applicable nForce chipset) and prices on the standard 1333MT/s 4GB kits stabilized below $100. By the end of its run the fastest DDR3 was still roughly equal bandwidth and latency of the average consumer DDR4 kits in 2017, 10 years after introduction. (Provided of course a golden IMC and motherboard that could support such speeds.)
- Compatibility was insanely good: while DDR2 almost entirely cleared up the need to run matching DIMMs to guarantee proper performance, DDR3 could effectively be grab-bag mix-and-match and still run at rated speeds. Intel finally adopting an IMC for their processors certainly helped with this (as AMD had proved this kind of reliability was possible for years) but more importantly their DDR3 IMCs continued to support their MCH feature of asymmetric multi channel, “Flex Mode”, which allows any set of DIMMs of any speed or capacity to be paired up into both a symmetric multi-channel and asymmetric single-channel. This is why you start seeing more laptops from around 2010-2011 suddenly featuring strange 3/6/12GB RAM configurations using mismatched SODIMMs.
Emphasis on “at JEDEC speeds”, but more importantly “at IMC rated speeds” because JEDEC validated 3200MT/s in 2017, and yet Zen 1/Zen+ struggled tremendously with anything over 2666MT/s (and still do if you run 2Rx8/2DPC). Haswell-E also cannot run the highest JEDEC standard speed without overclocking in quad-channel. Many systems until 2019 are limited to lower speeds by default, with Intel’s 6th-9th gen Skylake derivatives sharing the same 2666MT/s limited IMC.
512MB PC133 SDRAM was absolutely a thing by 2001 when most machines were moving to DDR. I still have some on a few boards.
With about two systems ever that support those speeds, and none that support it in dual channel without winning the silicon lottery. Unlike later DDR standards, DDR1 did not have any sort of SPD profiling. The manufacturer may have tested a maximum of 330MHz on their test equipment, but nobody made a memory controller that could handle those transfer speeds 1:1, and often you were left running 4:5 or lower offsets, effectively kneecapping the speed of the RAM by constraining the bus its attached to to a lower transfer rate than the RAM itself. (I.E. MCH at 400(3.2GB/s) while DRAM is at 660(5.3GB/s). Besides that, any DDR kits over 600MT/s were exclusive limited edition DIMMs made for bragging rights, similar to DDR2-1250 and DDR3-3200. The fastest commercially viable DDR1 was 500-550 with 500 already being a decent challenge for 1:1 MCH:DRAM below 3v.
As far as I know only the CAS latency could go lower, to “1.5”, and was a marketing and SPD trick from GEIL. Only a few NF4U boards supported it with Athlon 64, and no Intel boards officially worked with anything lower than CL2. Otherwise the rest of the timings had to effectively remain at 2-cycles in order for DDR to function properly.
Dual-channel DRAM was introduced with RDRAM in 1999 on Intel i840, then again at the end of 1999 with SDRAM on ALi’s Aladdin 7 chipset. nForce 420-D didn’t introduce dual-channel DDR until the end of 2001.
Opterons killing Pentium 4s in everything is a story as old as the release of K8 Opterons. No amount of faster DRAM/MCH will save a P4.