I recently built this computer for gaming primarily, but was curious as to why BIOS is only reading my RAM at 800MHz. It's got that dual threading (I can't remember the word for it, apologies if that's incorrect) thing, and given the exact halving of the advertised speed, I figure that's probably why, but just in case I'm getting a second opinion.
The 'DDR' in your DDR3 memory is short for 'double data rate' which means that it transfers data on both the rising and falling ends of the clock, if I remember correctly; what this means is that the memory is effectively running two transactions per clock cycle, and so you're getting an effective 1600Mhz even though the system is detecting it as 800Mhz. At least, that's my simplified understanding of how things work; feel free to correct me if I'm wrong, anyone.
download and run CPU-Z. If this program says your running at 800 MHz then you are actually running at 1600 MHz. If it says your running at 400 MHz then your running at 800 MHz. this is because of the (DDR) duel data rate. The data rate is multiplied by 2 .
to the previous posters. Although you are both correct, please remember not all Bios readings are the same. Some will give the single data rate and some will give the full data rate. This means there needs to be a check somewhere else for conformation that the ram is actually running the proper data rate.