Whats real mode and protected mode?
Also whats ring0 and ring3?
Posted on 2002-12-11 00:29:53 by clippy
"Real" and "Protected" mode are names given to different CPU modes that govern how the processor behaves when doing things like addressing memory and handling program execution. For the programmer, the major difference is that while Real mode uses a 20-bit segmented memory model, (memory is addressed in segment:0ffset pairs. segment*16+offset) in 32-bit Protected Mode the segment register is a descriptor, and registers are used to address a flat 4gb range of memory. There is also a rarely used 16-bit Protected Mode. And as well there are strange 'hack' modes like "Flat Real Mode" that you can achieve if you are brave enough to poke around. Protected Mode offers other advantages over Real mode such as segment protection and native multitasking.

Ring0 and Ring3 refer to priveledge levels of the CPU. There are four different levels in all, but AFAIK Windows only allows for the two. Ring0 is the mode the kernel runs in and it allows for total control of the CPU. Ring3 is what user applications run in. It's a restricted level that does not allow the application to access certain registers and restricts access to hardware and memory. These priveledge levels are only significant in Protected Mode, ergo Real Mode applications are free to tinker with the computer in whatever way they like.
Posted on 2002-12-11 01:32:44 by iblis
Nice Explanation.
Thanks Iblis.:alright:

Btw, your postcount reads - 404:grin:
Posted on 2002-12-14 23:30:51 by clippy