Re: When to use the /3 GB switch
From: Mike Hodgson (mike.hodgson_at_mallesons.nospam.com)
Date: 02/21/05
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Date: Mon, 21 Feb 2005 17:12:00 +1100
With 3GB of physical RAM in your box, no you shouldn't enable the /3GB
switch.
This switch would be better off called the 1GB switch rather than the
3GB switch because what it actually does is reduce the kernel mode
address space from 2GB down to 1GB thereby allowing the user mode
address space to use 3 out of the 4GB of virtual addresses in a Win32
application. The maximum addressable memory in a 32-bit application is
4GB (2^32 bytes). Windows splits this into 2 parts - the user mode
address space and the kernel mode address space. Note, these are all
virtual addresses and are mapped to physical RAM as needed. By
specifying /3GB in boot.ini you're altering the 2/2 split to be 3/1 so
the kernel code has less memory to play with.
With 3GB of physical RAM in your box, the absolute most physical RAM an
app could play with (assuming nothing else was running on the box) would
be (3GB - O/S RAM). So, if the kernel needs at least 1GB, that only
leaves a max of 2GB left, which is the standard user addressable
memory. So telling the kernel it can only use 1GB is pointless, may as
well leave it at the standard 2/2 split.
To answer your other question, /3GB is still supported in Win 2003 (I
think) but Microsoft recommend using the /USERVA switch, which is new to
Win 2003. /USERVA allows a greater granularity so you can specify, for
example, /USERVA=2560 to indicate that the user mode address space is
2.5GB and the kernel mode address space is 1.5GB.
HTH, sorry about the waffle. :-[
-- *mike hodgson* |/ database administrator/ | mallesons stephen jaques *T* +61 (2) 9296 3668 |* F* +61 (2) 9296 3885 |* M* +61 (408) 675 907 *E* mailto:mike.hodgson@mallesons.nospam.com |* W* http://www.mallesons.com Josh G via SQLMonster.com wrote: >I have a new installation of Windows 2003 Standard server with SQL 2000. >And 3 GB of Memory installed. Should I use the /3 GB switch? Is it even >support in windows 2003 standard edition? > > >
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