Why Does Microsoft® Windows Vista™ Report Less than the Actual Amount of Memory Installed?

Problem:
Why Does Microsoft® Windows Vista™ Report Less than the Actual Amount of Memory Installed?

Discussion:
Windows Vista automatically allocates a certain amount of memory for system use. The amount varies but is at least 1 MB. Only the unallocated memory is reported by Windows Vista programs (e.g., Welcome Screen, System Information, System).

Resolution:
On a system configured with 4 GB of random-access memory (RAM), Microsoft® Windows® reports 3.0 to 3.8 GB of available memory. The same behavior is seen in Linux and other operating systems, as this is a limitation of 32-bit addressing used in IA-32 systems.

Note: At this time, Dell portable systems reserve 1 GB of memory for input/output (I/O) space in the basic input/output system (BIOS), making the total memory available 3,000 MB, which equals 3 GB. This is set in the BIOS and cannot be changed by the user.