does pc800-45 ram interchange with pc800-40 ram?

Yes, in most cases; it's the latency in nanoseconds. Very expensive stuff nowdays. Check out the link below for the full scope.

The 40ns skill "40 nano-seconds" (a nano-2d is one billionth of a 2d) and refers back to the get right of entry to time it takes to circulate information between the pc and the memory. frequently the motherboard producer will rfile this variety of memory which you elect; however, contained whilst it comes to get right of entry to time, it would not harm to get the memory with the 'decrease' huge form no remember if that's no longer too lots greater high priced than the different. in the experience that your pc can get right of entry to the memory at larger speeds, that's greater useful to get the only with quicker get right of entry to time, yet it won't harm in the experience that your pc can not cope with the decrease huge form. on your case, 40 nanoseconds is quicker than 40 5 nanoseconds, so which you will get the 40ns specified memory.

45 Milliseconds compared to 40 Milliseconds. Yes, it will. (45 is the slower one. You won't notice)

is that rambus ram? it should..