- The system BIOS has reserved physical memory for graphics or for other peripherals.
- Your computer has more than 3 GB of system memory installed.
You will see this reporting change in the following locations:
- The RAM value in the Welcome Center.
- The Memory value at the bottom of the My Computer windows.
- The Memory (RAM) value in the System Properties windows.
- The Total amount of system memory value of the View and Print Details page of the Performance Information and Tools item in Control Panel.
- Installed Physical Memory (RAM)
- Total Physical Memory
- Available Physical Memory
- The Performance tab in Task Manager
- DirectX Diagnostic Tool (DXDiag.exe)
On computers that have a 32-bit operating system, more than 3 GB of system memory, and with a version of Windows that is earlier than Windows Vista SP1, users will see a larger difference in how much memory is reported as available to the operating system compared to how much physical memory is installed. This is because some physical address space must be reserved as I/O regions for memory mapped peripherals. These I/O regions are allocated between the 3 GB physical address and the 4 GB upper physical address limit.
Physical memory addresses that are mapped to these I/O regions cannot be used to address physical system memory. These addresses also cannot be used to prevent the operating system from using some physical memory that would ordinarily be accessed between the 3GB physical address and the 4GB upper physical address limit. The size of these I/O regions varies from system to system because they determine the type and configuration of the system’s peripherals.