Questions tagged [real-mode]
For questions about switching hardware into real address mode
11 questions
-1 votes
0 answers
95 views
How to tell gdb the default opsize, so it can debug multi cpu mode code (without a weird dissassembly output) [closed]
I've made my own kernel. It has 32-bit pm, 16-bit pm, and 16-bit real mode code. I use Qemu to emualate an i686. And when i debug the mode switch parts, the code runs and works. However, the ...
6 votes
1 answer
545 views
Can you write to the GDT on Windows 95 from protected mode? Why, and how?
Can you write to the GDT (Global Descriptor Table) on Windows 95 from protected mode? Why, and how? In some old notes of mine, I have: "In Windows 95 the descriptor tables are accessible from ...
- 1,551
26 votes
4 answers
5k views
How can a 32-bit x86 CPU start with reset vector 0xFFFFFFF0 even though it starts in 16-bit real mode?
As far as I know, x86 CPUs start up in 16-bit 'real' mode (maybe some don't). The reset vector is 0xFFFFFFF0 (in most CPUs and in this context) In this 16-bit real mode, we can only access 16 bit ...
- 363
1 vote
2 answers
441 views
8086 assembly relative addressing issue [closed]
This tiny program puts a few A's into the text mode buffer of an ms-dos pc. But only works if the number of repetitions (CX) is loaded with a direct value. If I try to read that from memory, i.e. ...
- 785
14 votes
2 answers
3k views
Are .COM executable binaries real mode or protected mode?
Windows and DOS binary executable files with the .EXE extension have an MZ header in them and nowadays also a PE header. But before these there used to also be .COM binary executable files and they ...
- 8,214
43 votes
3 answers
6k views
80286 can switch from real mode to protected mode - but why not back?
It's been a while, but I've read in a system programming book that you could switch your Intel 80286 CPU from the normal real mode to a more powerful protected mode. I clearly remember that they said ...
- 1,225