The indication of the memory can be quite confusing in Windows 8.1, usually memory is always less than the really installed memory!
Now don't panic, if you use a 32-bit Windows 8.1 so only 3.5 GB used.
A 32-bit version of Windows 8.1 report that only 3.5 GB of usable memory available on a computer with installed 4 Giga Byte memory. This is a normal worth under Windows 32-bit usually varies from system to system between 3.2 and 3.51 gigabytes depending on the computer hardware!
But also for Windows x 64 (64-bit), it may happen that the available memory is different from the actually installed RAM. Especially if you have for example on-board graphics card with 256 MB, Windows must assign this memory within the first 4 GB of address space.
There are also cases where the memory chip is actually defective! Or, there are several additional situations that could cause the usable RAM to be less than expected.
See also:... Restrict maximum memory under Windows!
... How can I see if i have x64 Edition or Windows x32/x86 on Windows 8/8.1?
FAQ 207: Updated on: March 22th 2014 21:19