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60424Re: Help with computer

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  • Roger Hamlett
    Dec 2, 2007
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      > Interesting. MS claims that 32 bit versions of Vista use up to 4GB. I
      > Googled this and got some interesting answers.
      >
      > In XP, if you have an integrated video system, it steals main memory and the
      > reported amount is smaller by that amount. But 512MB is awfully large
      > for integrated graphics.
      >
      > Seems like the answer for Vista is a whole lot more complicated and a whole
      > lot OT to this group.
      >
      > On 11/29/07, Murray Hammick <mphammick@...> wrote:
      >> I have Vista on a Quad core PC with 4 gig of Ram loaded.
      >>
      >> The system only shows 3.25gig for some reason. perhaps that is the max on
      >> VIsta.
      >>
      >> Murray
      The 32bit versions of Vista, and XP, can both directly _address_ 4GB.
      However,out of this address space has to come a whole lot of stuff.
      Spaces for the BIOS, the video card BIOS, a huge window for the video,
      even when it is not shared, areas for network adapters, etc. etc..
      It is typical to lose about 256MB, on systems designed to keep the loss
      small. On normal systems 300MB, to 768MB is 'typical' (the latter in
      particular on systems supporting double video cards...).
      Now, there is a way round this, called 'PAE'. Basically, a modern
      'smarter' bank switching technology, allowing the memory manager to
      switch in different memory areas according to what is using them. This
      was first implemented in NT. Latter it appeared in W2K, and then it
      arrived in XP SP1. At this point, basic XP, could give you 4GB of
      'visible' RAM, on sytems with this fitted, and the hardware to implement
      the switching. Only a couple of weeks latter, MS introduced a 'hotfix',
      and though PAE was left enabled (it is used for some other things
      related to system security), the maximum addressable, dropped back to
      4GB, except on the server releases...
      Vista32 retains this limit.
      Now, part of MS's statement about disabling the feature on XP, was that
      for machines with only 4GB, it was costing more than you gained.
      Switching to supporting the extended addressing, implies that huge
      numbers of table entries inside the OS, have to grow from being 32bit
      values, to a larger size. This makes handling slower, and increases the
      size of these tables. So though you then 'see' 4GB of RAM, the useable
      area, does not grow by much, and you lose perfomance. You also need to
      remember, that if you are running a typical application, _it_ cannot see
      4GB. Normally XP/Vista, allocate 2GB _max_ to a application. There is an
      option (/3GB), which increases this allocation, but it also requires the
      application to have been compiled to support the large address space model.
      The difference, really appears, when you run a 64bit OS (where the page
      switching is no longer needed, and the register addresses in the
      processor directly support the extra size), with an application that has
      also been written to support this. Then with even more memory (8GB+),
      the performance on large database application, and raphics, really flies.
      I am typing this to you, on a XP32 Pro 'session', inside a Vista64 box.
      The XP session, has 3669MB of memory available. The Vista host, has
      8061MB available. This is using VMWare, which really shows how MS,
      should have implemented 32bit support for the 64bit OS. Inside the
      session, I can even run half a dozen peripherals, for which there are no
      64bit drivers, whilst at the same time gaining full 64bit performance
      outside.
      Run up XP directly (without VMware), and the memory drops to only 3248MB.

      Best Wishes
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