Text 27234, 46 rader
Skriven 2007-01-22 06:47:22 av Jeff Guerdat
     Kommentar till en text av ED VANCE
Ärende: Re: duo core - what for?
================================
ED VANCE wrote:

> As you probably heard me brag, I have 3GB of DDR RAM in this XP box.
> 
> Would I have to use a /2GB switch in boot.ini to get 2GB for apps and
> 1GB for the OS?

...

> I just jumped to CMD and saw that bootcfg/? gives me a listing of
> allowed commands, so I now know XP uses it.
> 
> I see there is no /2GB switch only a /3GB switch.
> One of the MSKB articles referred to its' use for just SCSI, but I think
> it can be used with IDE and SATA.

As you found, it's only an issue with systems that have >3GB of RAM. 
Since the OS lets processs occupy up to 2GB of RAM in the first place, 
that means the OS only gets 1GB for itself with your 3GB.  The switch 
would simply have no effect.  While I haven't tried it, you could always 
add the switch to boot.ini so you're all set when (not if ;) ) you put 
the full 4GB into place.

I suspect the reference to SCSI is due to most machines with 4GB or more 
of memory tend to be special cases such as servers and high-end 
workstations which may well employ SCSI disk subsystems for performance.

> How did you get so smart in knowing all this complicated stuff so you
> can help us other users???

Some of it is just dumb luck, tripping over a piece of information in 
reading about something else.  Most of it, however, is due to 
experience.  For instance, I already knew (as of about 1999) that 32 bit 
OSes/applications had issues with accessing 4 full GB of RAM.  This was 
because we were running into application crashes while simulating new 
chip designs in software.  The job would grow to 2GB of RAM usage and 
unexpectedly go away.  I found in Sun's Solaris that the default limit 
to a process was 2GB, even if you set the environmental variable to 
"unlimited".  There was a very specific number to be used to allow the 
process to use as much RAM as possible.  I forget exactly but I think it 
was something like 3.6GB.  Another way to look at this is that a signed 
integer for a 32 bit OS is 31 bits (2GB) with a "+" or "-".  Basically, 
we needed to ignore the sign bit.  So, with that in mind, I suspected MS 
would also have issues with >2GB of RAM in a machine.
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