Why not 64 bit under 32?

[Kenneth Lantrip]

Why can't 64 bit code run under a 32 bit OS?

I understand that perhaps you could address the memory but why not have
some mixed in 64 bit instructions inside a 32 bit program running under
a 32 bit OS?

Does the processor have to change modes like the 386 did from a 286?

Just curios.

Kenneth

 

[Jack Klein]

Why can't 64 bit code run under a 32 bit OS?

I understand that perhaps you could address the memory but why not have
some mixed in 64 bit instructions inside a 32 bit program running under
a 32 bit OS?

Does the processor have to change modes like the 386 did from a 286?

Just curios.

Kenneth

Did you have a question about the C programming language, which does
not define '64 bit code', '32 bit OS', or 'processor modes'?

 

[Jim]

Why can't 64 bit code run under a 32 bit OS?

I understand that perhaps you could address the memory but why not have
some mixed in 64 bit instructions inside a 32 bit program running under
a 32 bit OS?

Does the processor have to change modes like the 386 did from a 286?

Just curios.

Kenneth

Many compilers support a 64-bit long long type. Check your compiler's
documentation.

Jim

 

[Dan Pop]

Why can't 64 bit code run under a 32 bit OS?

Who said it can't? I've spent about one year working with 64-bit code
under a 32-bit OS. Not to mention Windows NT on Alpha, which is a 32-bit
OS implemented with 64-bit code. Ditto for certain OpenVMS/Alpha
versions.

I understand that perhaps you could address the memory but why not have
some mixed in 64 bit instructions inside a 32 bit program running under
a 32 bit OS?

Engage your brain: if it's a 32-bit program, how can the processor
guess that certain opcodes must not be interpreted as 32-bit opcodes?

Does the processor have to change modes like the 386 did from a 286?

What was your C language question?

Dan