INTRODUCTION
After you install Windows Vista Service Pack 1 (SP1), the memory (RAM) value reported by Windows Vista may increase if the following conditions are true:
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The system BIOS has reserved physical memory for graphics or for other peripherals.
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Your computer has more than 3 GB of system memory installed.
This change occurs because Windows Vista with SP1 reports how much physical memory installed on your computer. All versions of Windows NT-based operating systems before Windows Vista Service SP1 report how much memory available to the operating system. This change in Windows Vista SP1 is a reporting change only.
You will see this reporting change in the following locations:
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The RAM value in the Welcome Center.
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The Memory value at the bottom of the My Computer windows.
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The Memory (RAM) value in the System Properties windows.
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The Total amount of system memory value of the View and Print Details page of the Performance Information and Tools item in Control Panel.
Additionally, the System Information tool (Msinfo32.exe) now displays the following entries on the System Summary page:
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Installed Physical Memory (RAM)
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Total Physical Memory
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Available Physical Memory
The installation of Windows Vista SP1 will not change the reporting in the following diagnostic tools:
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The Performance tab in Task Manager
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WinVer
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DirectX Diagnostic Tool (DXDiag.exe)
Important This change in reporting does not address all differences in memory reporting. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
935268 Components of the user interface in Windows Vista report slightly different values for the total physical memory that is available on the computer
More Information
Before the installation of Windows Vista SP1, Windows Vista displayed how much system memory was available to the operating system. For computers that have 3 GB or less of physical memory installed, the reported memory value can sometimes be somewhat less than the memory physically that is installed. These differences are because of the BIOS and possibly driver reservations of physical memory. For example, some BIOS implementations allocate some physical memory for the graphics adapter. Typical sizes are from 8 MB to 128 MB for graphics. Other sizes are possible. The BIOS and some drivers may reserve physical memory for other peripherals or purposes. These reservations are reasonable and are part of the usual operation for a computer. However, they do reduce how much physical memory is available for use by the operating system and applications. These reservations affect both 32-bit and 64-bit computers.
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.
References
For more information about how system memory is reported in Windows Vista, click the following article number to view the article in the Microsoft Knowledge Base:
929605 The system memory that is reported in the System Information dialog box in Windows Vista is less than you expect if 4 GB of RAM is installed
