Lawrence Plummer wrote:
> XP (32-bit) can use up to 4GB, with default configurations giving 2GB to
> applications. This can be altered by changing the boot.ini file. There is
> a /3GB option to increase process space to a max of 3GB, but it can be
> somewhat problematic (see http://support.microsoft.com/kb/833721/en-us). XP
> (64-bit) can use up to 128GB. Addressing is always done using unsigned.
>
Xp was another example of poor design by microsoft.
The intel processors had limits of 4gb per *program* running so one
program could not access more than 4gb but you could have 2 programs
each using 4gb. Microsoft choose not to support this or did not know and
so *everything* running has to fit into 4gb. They could have fixed this
without the need to go to 64bit but again choose not to. This is why
Linux does not have this problem. In fact with a little creatitiy XP
could have not even had the 4gb limit at all. The proccessor has 6
registers for addressing memory each register could be loaded with a
different 4gb slab of memory offering 4gb for the code, and the
remaining 5 registers offering 20gb for the data. Again this is on a per
program basis. Again they chose not to support this. The additional
advantage is that each register can be security protected so that
malicious programs could not execute code or write modify the program
code again they chose not to support this hense the buffer over run
problems etc. One day Microsoft may drag its 32 bit operating system in
line with the hardware caperbility of the processors has the 486 let
alone the pentium 1 series....
As far as signed or unsigned addresses go ALL adresses are unsign as far
as the processor is concerned but because most compilers treat pointers
to memory as numbers they must mnake the choice of signed or unsigned
and most compilers stupidly decided pointers where signed thereby
throwing away 50% of the available addressing space. GGGRRRRR. Same
thing happened with file sizes two hense the 2gb limit on a file size
when it could have been 4gb.
sorry for the rant
James
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