Application 32/64 bit and OS 32/64 bit

Question

I would like to know the following things :

1. Can a 32 bit application run under a 32-bit operating system?
2. Can a 32 bit application run under a 64-bit operating system?
3. Can a 64 bit application run under a 32-bit operating system?
4. Can a 64 bit application run under a 64-bit operating system?

Thank you.

Answer 1

Yes. If not directly (case 3 is tough), then by means of emulation/virtualization.

Answer 2

1. Yes, of course...
2. Yes
3. No
4. Yes of course...

Maybe you should read something about computers, CPUs and x86 acrhitecture in general.

Answer 3

1) Yes 2) Yes 3) No (As said above without running a virtual machine or emulating or something) 4) Yes

http://www.techsupportalert.com/content/32-bit-and-64-bit-explained.htm

There is some reading for you to help with why :)

Answer 4

Yes Yes No Yes

In a 32 bit system and application , variables are of size "x". In a 64 bit system and application , variables are of size "2x"

thus a pointer in a 64 bit system can point to twice as much data as a pointer in a 32 bit system ... thats why a pointer in a 64 bit system can access anything in 32 bit application and in a 32 bit system a pointer can access only access half of the data it is supposed to in a 64 bit application...