Finally! 4GB of True 1.8V DDR2-800 Memory!

One of the things that continually burns me up on PC Memory is the over-marketing of the synchronous clock of today's Double Data Rate II (DDR2). It was bad enough when latency was jacked up high (worse) for higher synchronous clock rates and performance was no different. I touched on how to calculate real-world "latency" on DRAM modules near the end of my Spring 2007 PC Assembler's Quick Guide.

But now the majority of vendors are claiming DDR2-800 (JEDEC PC2-6400) and higher synchronous clocks that utterly violate the JEDEC spec of 1.8V that require you to run them at 2.0-2.1V typically, 1.9V if you're lucky, and 2.2V+ are not uncommon either. It was less common at DDR2-667 (JEDEC PC2-5300) for them to do this, but now almost defacto standard with DDR2-800 (even in notebook SO-DIMMs, almost guaranteeing incompatibility). To even misinform the consumer more, some even report the DDR2-667 timings (e.g., CAS 5), and the DDR2-800 gets worse (e.g., CAS 6 is common), and that's only when you over-volt too. That's why I've just stuck with DDR2-667 for now, inexpensive 1GB HP parts when rebates are offered, along with a JEDEC compliant 1.8V DDR2-667 parts from a few vendors.

Luckily I noted last week the Transcend JM4GDDR2-8K 4GiB kit, two (2) 2GiB DIMMs that are fully JEDEC DDR2 Compliant at 1.8V for PC2-6400 (DDR2-800) rated with CAS 5 timing. It is a very inexpensive kit available for under $80 at the time of this writing. It replaced my 8-month old Patriot PSD24G667K 4GiB kit, also two (2) 2GiB DIMMs that were fully JEDEC DDR2 compliant at 1.8V for PC2-5300 (DDR2-667) rated with CAS 5 timing.

On the eVGA 112-CK-NF77-A1 Mainboard (eVGA "NF77") with the nVidia GeForce 7150 IGP (with nForce 630i MCP combination), the timings were reported by Serial Presence Detect (SPD) as follows ...
- Transcent DDR2-800: CAS 5, RAD 4, RP 4 and RAS 15 (5-4-4-15)
- Patriot DDR2-667: CAS 5, RAD 4, RP 4, RAS 15 (5-4-4-14)

Essentially the exact same timings, but at a 20% synchronous clock improvement. CAS 5 at DDR2-800 is basically like having CAS 4 at DDR2-667, a RAS of 15 at DDR2-800 closer to a RAS of 12 (than 13) on DDR2-667. Most people are reporting major boosts in performance as memory latency is always a major performance hit. I.e., RAS 15 on DDR2-800 is 37.5ns (26.6MHz "equivalent" -- yes, two-six megahertz like your old 80386 clock, that's how much DRAM technology sucks at latency, such as just getting the first page read). RAS 15 on DDR2-667 is 45ns (22.2MHz "equivalent"). And this is without over-clocking/volting, stock clock and timing at 1.8V.

The overwhelming majority of DDR2-800 modules are, again, over-clocked because they are over-volted beyond 1.8V -- 2.0-2.1V is extremely common. That's why most come with heat spreaders, which also hide the true synchronous clock (reported in latency). If you're running at JEDEC compliant 1.8V, you don't need spreaders, and only need to add spreaders if you want to over-clock/volt. Frankly, I want my memory chips to last, so I'll run them at stock, keep the ambient temperature in the case low, and possibly consider heat spreaders later.

If you just want basic performance, such as a low-end dual-core system, then DDR2-667 will do fine, although make sure you get 1.8V. If you're looking for optimal performance while being compatible, get a DDR2-800 which runs at a true, JEDEC compliant 1.8V and has a true CAS 5 and similar 5-5-5-15 timings or better at actual DDR2-800. So many out there are 6-6-6-18 or similar, and that requires an over-volt to 2.0V+ to get (and some want you to do 2.3V+ to get CAS 5 or 4 at DDR2-800). The Transcend JM4GDDR2-8K 4GiB kit makes a great selection, and just separately pay $5 more for the heat spreaders if you really want to add them (especially if you're going to over-clock/volt to DDR2-1000+).