60426Re: [ccd-newastro] Re: Help with computer
- Dec 2, 2007Wow !!
Thanks for the explanation. I am afraid I could not track all of it - but I get the drift of what you were saying - I think.
Given the need for astro computers to multi task - are you suggesting that we could reconfigure a PC to make it considerably more efficient ?
Roger Hamlett <roger@...> wrote: > Interesting. MS claims that 32 bit versions of Vista use up to 4GB. I
> Googled this and got some interesting answers.The 32bit versions of Vista, and XP, can both directly _address_ 4GB.
> 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
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
Run up XP directly (without VMware), and the memory drops to only 3248MB.
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