DDR2 Memory

So what's the deal with DDR2-667 vs. DDR2-800 memory?

First of all, when it comes to memory, the more you have, the better it is... period.
The DDR2-800 and the DDR2-667 comes in 2 GB chips so you can fit 4 GB in (read more on DDR2-800 later) the 2 available slots of most notebooks.

Second, your OS & chipset have a big impact on how much memory your system can see, and effectiuvely use.
3GB was the old barrier, this was due to the Windows XP OS and the pre-965 Intel chipsets (on Intel CPU's). The other memory was there, but was allegedly used by "upper system functions". Sounds a little fishy to me, memory that is there but you can't see or get any benefit from?
Until now we were only offering 3GB memory configurations. Now we have 64 bit Windows Vista (for better or worse) which supports more memory than we can effectively put in the system.

For AMD on the other hand. The Turion X2 supports DDR2-800, so keep that in mind if you are looking at an Assassin. You have to weigh the benefits and drawbacks and look at your program usage to determine if 20% more bandwidth (ie faster transfers) are more important than twice the amount of RAM. Usually it is the latter, and again, more is better.

Third, even though the new Intel Centrino Santa Rosa chipset utilizes a 800 Mhz front side bus, the memory channel still only supports 667 Mhz!?! I know, I know... what was the point? This is very confusing, and I believe Intel is making it deliberately hard to find this out so people will naturally assume the memory is 800 Mhz. The only thing I can think is that they needed something to "add-on" for the next chipset revision because many people think, "Oh yea, now I am going to be cranking extra clocks on my memory", which would boost system performance, but unfortunately that is not the case. We were the first notebook vendor to sell DDR2-800 because some people just have to have it. It's ok, we're the same way. We want the fastest and the best possible, but in this case, the 4GB of DDR2-667 is a much better route to go for performance.

Forth, what about memory brands? At KillerNotebooks we are all about quality and building bulletproof computers. We started with the idea of using best of breed componets, which is why we use OCZ Technologies memory. For a short period we actually fell for the idea that all RAM was created equal and "the memeory chips were the same." Well, we found out the hard way they are not! We used Corsair, which we, like many others considered high quality RAM. The rate at which Corsair failed and caused the BSOD was ridiculous. Rest assured, we use OCZ, and it costs way more (almost 40%), and as far as we're am concerned... worth every penny.

Here is an example. Recently I had the misfortune of having to use an Executioner with a Core Duo T2700 2.33 Ghz CPU. No slouch by any means, but also no T7600 Core 2 Duo with 4 GB of RAM (that I usually use). For multi-tasking I was using Adobe Photoshop CS3, Dreamweaver CS3, SnagIt, Thunderbird, about 8 Firefox windows, WinAmp, MBall, and at times Adobe Fireworks and AVG antivirus in the background (not scanning, just resident). I could feel the lack of memory big time. This what I consider multi-tasking, cut that list in half, and you just have some programs open... for multi-tasking you will want large amounts of RAM.

DDR2 SODIMMS for notebook-pc's offer a number of improvements over the previous DDR1 generation memory solution. These include low power consumption, improved thermal characteristics, and high bandwidth. All this results in greater performance per watt and improved battery life compared to other memory standards.

Bandwidth is the rate at which data can be sent from the DRAMs over the memory bus. Lower timings allow faster access to the data, while higher bandwidth allows access to more data. Applications that access large amounts of data - either sequentially or randomly - usually benefit from increased bandwidth. Bandwidth can be increased either by increasing the number of memory channels (i.e. dual-channel) or by increasing the clock speed of the memory. Doubling memory bandwidth will never lead to a doubling of actual performance except in theoretical benchmarks, but it could provide a significant boost in performance. Many games and multimedia benchmarks process large amounts of data that cannot reside within the cache of the CPU, and being able to retrieve the data faster can help out. All other things being equal, more bandwidth will never hurt performance.

RAM Latency Explained

CAS

Column Access Strobe (sometimes Column Access Select). This is actually the last stage in finding where data is physically located in RAM. Data is stored in an array of columns and rows–the row is selected first, then the column is selected and the data in memory is either read from or written to. CAS is the amount of time, in cycles, between receiving the column access command and acting upon it. It is usually a value of 2, 2.5, or 3 for DDR and 4-5 or 6 for DDR2.

tRCD

RAS (Row Access Strobe) to CAS delay. This is the delay, in number of cycles, between finding the row of a location in memory, and finding the column. This value is usually between 3 and 5 cycles, but it doesn't tend to have a huge impact on performance. Sequential bits of data are usually stored along the same row in memory, so rows are not re-selected nearly as often as columns.

tRP

RAS precharge. This is how much time it takes for the memory to stop accessing one row and start accessing another. Like tRCD, this value is typically between 3 and 5 cycles for modern memory systems. It can have an impact on performance when programs use large blocks of memory that span several rows.

tRAS

Active to Precharge Delay. This is the delay, in cycles, between the pins of the memory module electronically receiving a signal and the module starting the Row Access Strobe to locate and retrieve (or write) it. This is generally a pretty big delay, from 5 to 8 cycles on most DDR memories. But it also doesn't have a huge impact on performance, and should only make a big difference when memory access patterns change dramatically.