64 bit

[Robert Heller]

At Fri, 25 Jul 2014 14:03:19 -0500 Jeffrey Ollie <jeff at ocjtech.us> wrote:

> 
> On Fri, Jul 25, 2014 at 1:34 PM, John Dablin <jdablin at ntlworld.com> wrote:
> > On 25/07/14 08:46, John Ralls wrote:
> >>
> >> It might be. I don't think anyone has tried. Mingw64 would be required.
> >> Note that I also don't think that there's any good reason to, as GnuCash's
> >> data fits easily in a 32-bit address space.
> >
> > This is pure curiosity, but the maximum value of a 32 bit signed integer is
> > 2,147,483,647, so if that were cents it would represent $21,474,836.47. My
> > bank balance will never grow that high, worse luck, but a medium sized
> > business might have totals of that order. Does Gnucash use multi-word data
> > types to handle this, or would it cause an error?
> 
> The 32 bits in a 32 bit operating system refers only to the amount of
> address space (RAM) that a process can access.  It has nothing to do
> with the number of bits in data elements used by a program, which can
> be 64 bits, 128 bits, or even more.

It also refers to the integer CPU register size (and the native single1
instruction ALU ops) and also refers to the width of the data bus (how many
bit can be transfered in one cycle, although with modern '32-bit' processors
this is somewhat meaningless, given caches and pipelines, and such). All
*modern* 32-bit C/C++ compilers support 'long long int', which is 64-bits on a
32-bit machine. Most modern scripting languages also support (at least) 64-bit
integers as well (and some have support for some flavor of 'bignum', which is
an integer that has as many bits as it needs, dynamically growing as needed).

So yes, the only real hard limitation of a *modern* 32-bit processor (eg an
Intel i686 type processor), is virtual address space, which is about 3.5G
(about .5G is 'lost' to PCI address space). (The latest incarnation of the
i686's include PAE, which includes x86_64/amd64 processors in 32-bit mode,
which actually allows more *system* memory, but each *user-land process* is
still limited to just under 4G.)

The only restriction with running 32-bit x86 apps on a x86_64 processor
running a 64-bit operating system is the presence or absense of the 32-bit
system libraries. Some of the latest 64-bit Linux distros don't bother to
install the 32-bit libraries *by default*, but they can be optionally 
installed if needed.  I'm guessing the 64-bit Windows 7 and 8 do install the 
32-bit libraries.  I don't know what MacOSX 10.9 does, but I believe up though 
10.8 has both 64 and 32 bit libraries.
> 

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