Re: not exactly 4GB of RAM

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

Windows XP allocates 3GB of virtual address space to programs and 1GB to the kernel
and to executive components. A program must be designed to take advantage of the additional
memory address space.

Available switch options for the Windows XP Boot.ini files
http://support.microsoft.com/default.aspx?scid=kb;en-us;833721&Product=winxp

--
Carey Frisch
Microsoft MVP
Windows XP - Shell/User
Microsoft Newsgroups

-------------------------------------------------------------------------------------------

"Marc" wrote:

| Hi
|
| I have a Dell Precision Workstation 670 with 4GB of ECC RAM.
|
| BIOS reports 4GB. But Windows XP/SP2 reports 3.25GB of RAM
| (under My Computer|Properties and in Task Manager)
|
| Quoted from Dell Tech Support:
| -----
| Technically the Precision Workstation 670 can hold up to 12GB Maximum of
| physical
| RAM.
|
| The system BIOS or Setup Screen will show you 4GB of RAM. On a system
| configured
| with 4 GB of RAM, Windows shows 3.3 to 3.8 GB in Windows. 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.
|
| This is a limitation of a 32-bit architecture. The system can only
| address 4 GB
| of allocated memory. Allocated memory is made up of physical RAM, and
| any I/O space
| needed by devices. The way memory is allocated is that starting at 4GB
| the system
| allocated device I/O addresses working it''s way down. Normally this is
| not a problem
| but when systems have 4 GB of physical memory the addresses needed to
| address RAM
| overlap the space needed for I/O. In this case the need for I/O space
| takes precedence
| and the amount of RAM visible to the operating system and applications
| is limited
| to 4GB minus I/O Space.
|
| Example: If you have a total I/O range of 512 MB needed by all the
| peripherals,
| AGP Aperture etc in the system you have 3.5 GB shown as usable RAM in
| Windows.
|
| NOTE: Server systems are able to extend the address space with PAE
| (physical address
| extension). This options is not available on desktop and workstation
| systems.
| -----
|
| I absolutely understand that 4GB is a 32-bit limitation.
|
| However, my question is this:
| I have a 2GB machine and it does not get reduced by memory required by
| peripherals.
| Why is that? Same goes for my 1GB machines.
|
| Dell's explanation doesn't quite explain it all for me. I would think
| that this behavior could be changed by the BIOS. But before I argue
| with Dell, I would like to confirm that XP/SP2 can indeed "see" all 4GB
| and that it's a fault of the motherboard/BIOS...
|
| Thanks,
| Jay
.

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