How much RAM can XP Pro Ed. handle

S

seth_myhre

I am having a sreaming PC built mostly so I can have XP Pro instead of Vista
installed. One builder tells me that XP can only manage 2 GM of RAM, and one
"expert" as CES recently told me that XP can actually handle 3GB. Which is it?


FYI, my system will be an ASUS P5E (X38 chipset) motherboard, Intel 6600
Quad CPU, Nvidia 8600GTS GPU, WD 36GB raptor Hardrive for apps, and a WD 500
GB hardrive for files. I will use it for business, gaming, video editing at
the same time. I am a power multitasker. I get my info from PC magazines but
don't really know what I am talking about, does anyone have any comments on
this build regarding compatability, money wasted?
 
K

Ken Blake, MVP

I put 4 gigs in mine. Vista says I have 3.3 gig.


All 32-bit versions of Windows (Vista as well as XP), even though
they have a 4GB address space, can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but is
usually around 3.1GB.

Note that the hardware is using the address *space*, not the actual
RAM itself. The rest of the RAM goes unused because there is no
address space to map it too.
 
C

Colin Barnhorst

4GB. However, XP does not report the amount of installed ram but the amount
available to user programs. How much will display as available to user
programs varies from around 2.5 to 3.3 depending on the mobo and devices in
the computer. Modern mobos provide for memory mapped I/O and device
designers take advantage of this to enhance performance. However these
memory mapped I/O address spaces are protected from user programs and the
address range is not reported. Hence you don't see 4GB as available. There
is nothing inherent in XP that prevents it from using all 4GB of the 32-bit
address range. It is the BIOS that is reserving some of the space for
hardware buffering and such.

There is no particular reason why XP cannot report installed ram instead of
the amount available in the user space, but the latter is probably more
useful to know and that's how 32-bit Windows has always done it.

However, Vista x86 beginning with SP1 will be reporting the amount of
installed ram so the users who are testing the release candidate right now
are seeing 4GB on the system properties page. This only a change in what is
being reported, however. It does not change what is available to the user.
This change is NOT being retrofitted to XP with SP3.
 
T

Tim Slattery

seth_myhre said:
I am having a sreaming PC built mostly so I can have XP Pro instead of Vista
installed. One builder tells me that XP can only manage 2 GM of RAM, and one
"expert" as CES recently told me that XP can actually handle 3GB. Which is it?

Neither one. 32-bit XP, like other 32-bit systems has a 32-bit (4GB)
address space which must be used to access BIOS, video memory, etc, as
well as system RAM. See here:
http://members.cox.net/slatteryt/RAM.html
 

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