please forgive the beginner like questions since I am not really an asm programmer but I am interested.

1. is it possible to write a program/os in only 64 bit mode?

2. how does one find the limitations of the hardware on a machine, like VT capability and size of physical ram.

3. can assembler be "generalized" like C for other arch's? I suspect no but thought I would ask anyway.

thank you,
charles......

1. yes

2. this is hardware dependant, check your mobo and expansion card manuals, but there are BIOS calls that can provide basic mobo information.

3. no, it has to be ported to work with different instruction sets.

2. Also, CPUID gives you loads of info about the CPU instruction set and features. And if your programming in windows then there are a number of functions that give you info about ram, video and sound capabilities, motherboard info, etc.

I thought the CPU starts out in compatibility mode, so that 32bit OS can load? So doesn't the first part need to be 32bit before entering long mode?

Actually the CPU starts in real mode and only the boot loader needs to know that. The original question is about "program/os", so the answer is correct to say yes.

another question, can i acces 64bit registers with 32bit only x code?

edfed, no I don't think you can (unless you count MMX or Mac OS X's weird 32-bit hybrid kernel that can run 64-bit apps somehow).