Problem with new ram


Oct 19, 2011
prblm with ram

i just bought new ram of 2gb 850mhz

originally i had 2gb

now the total should be 4gb but system properties is showing

"3.25 usable"

i am unable to understand???
Memory management is a pretty complicated subject, but basically a 32 bit operating system is built around an address space of 32 lines. 2^32=4GB.

But it is worse than that. Intel CPU's use memory mapped input/output - devices are assigned address space that then cannot be used for memory.

The end result is that you generally have around 3.25 - 3.5 GB RAM available.

64 bit OS can address 2^64 or 4GB*4GB or a bunch of RAM, well 16 exabites (16 x 10^18). Limitation is generally the motherboard.