I went with PC2100 memory, not PC2700 or PC3300. Why? It’s not because I only needed PC2100 DDR RAM. If you were building a gaming or office PC with 266MHz DDR-RAM, you’d still shop for the memory with the highest rating. What makes a workstation or server different is Registered ECC memory.
Two to twelve times each year, a bit in memory gets inappropriately flipped. This can be caused by cosmic rays flying through your RAM or a decay of the minute radioactive isotopes found in your RAM – the impurity need only be a single atom. Most of the time, this flipped bit is unimportant. Maybe it’s a flipped bit in unallocated memory, or maybe it just altered the position of a pixel for a fraction of a second. If you’re unlucky though, this flipped bit can alter critical data and cause your system to crash. In our situation, a flipped bit could potentially alter our results significantly.
ECC memory provides error checking and correction facilities. By adding an extra memory chip, ECC memory makes your memory act in a similar way to a RAID array. In other words, when that lone bit is inappropriately altered, the memory is able to detect this failure and correct it.
FiringSquad has always had good experiences with Corsair memory, and so I went with two 512 MB sticks of registered DDR memory. In general, it’s not a good idea to rely on a single DIMM for a high-end workstation. Even though Corsair offers a lifetime warranty, replacing of a bad stick of memory still requires an RMA (shipping time), or a trip to Fry’s. Having a system built with two memory sticks means that you’ll still have a running system while you wait for the part to be replaced.
But I made mistake in selecting the memory. There is no such thing as “cost-is-no-object” -- you are always on a budget. In selecting the memory, I decided that a gig of RAM would be plenty. Of course, once the system was built and we started running some more test applications, I realized that 1GB was just enough to provide data to one CPU. (Some of our datasets contain over 800MB of data). Our system needed at least 2GB of memory. By going with two 512MB DIMMS instead of two 1GB DIMMS, I have limited the system upgrade potential to 3GB rather than 4GB (unless we are willing to sacrifice the two 512MB DIMMS). Two lessons:
1. Make sure you know your requirements when you build the PC
2. You can never have too much memory … really.