Questions tagged [protected-mode]
Aspects of the protected mode of x86-based CPUs: entering and exiting the mode, programming in it, particular features and characteristics.
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Operating systems running programs in 286 16-bit protected mode
I'm looking for existing, old operating systems which can run programs in 286 16-bit protected mode. (Please note that in this question I'm not interested in 16-bit programs for the 8086 and 80186, or ...
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Were there any protected mode PC booters?
The "PC booter" era lasted until around 1990, but the 386 was generally released in 1986. That's quite a narrow window, but it strikes me that a protected-mode booter game, using non-...
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What is the purpose of DPMI interrupt 31h function 300h?
In the DOS Protected Mode Interface, int 0x31 function 0x0300 is "Simulate Real Mode Interrupt". I found some documentation that says:
You may use this instead of the INT nn opcode to ...
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Example Windows 3.11 286 protected mode program - how long did Win 3.1 286 protected mode last?
This ancient program to sort a text file was used as a test case for Windows 3.1 286 protected mode. Since the 64 KB segments can't overlap, it read the file 63 KB per 64KB "chunk" and would ...
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BIOS support for 286 Protected Mode
Did BIOS on 286 systems provide support for the Protected Mode? On a 386, the BIOS can be fairly easily accessed from protected mode using the Virtual 86 mode, but since 286 did not officially support ...
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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 ...
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The move to protected mode on x86 [closed]
When I learned programming, the programmer of the CPU had direct memory access. That is, the Z80, the 8086/8088, 6502, and so on. I don't know of any real use of the 186, but at least the 286 ...
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How much slower was the 286 in protected mode?
I am given to understand that if the 80286 is run in protected mode, it is slightly slower than real mode, due to memory protection checks taking extra clock cycles.
Just how much slower is it? Either ...
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Why did "protected-mode MS-DOS" never happen?
Software written for MS-DOS used DOS extenders as early as on PC/AT (DOS/16M), and starting from i386-based systems, DOS extenders became really widespread.
I'd think it was pretty obvious at the time ...
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Were Windows 3.x applications dependent upon 80286 instructions?
While Windows 3.x operating system stuck to the 80286 platform, did applications compiled for Windows 3.x have to use 80286 instructions explicitly or be aware of the 80286 memory layout?
Or was it ...
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XMS function 0Ch "Lock Extended Memory Block"
I have a question about this function that has bugged me for years, so I decided to let this community a try :) So, this function supposedly locks a XMS extended memory block in place, and returns an ...
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Did any software attempt to perform 8086 emulation on the 80286 using LOADALL, in the vein of the later virtual 8086 mode of the 80386?
I know that Virtual 8086 mode was added on the 80386 to make it possible to run old applications in a Protected Mode environment.
The 80286 had a lot of shortcomings, such as not being able to switch ...
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Why does the ‘Get Next Selector Increment Value’ DPMI call exist?
In DPMI, interrupt 0x31 services 0x0000 and 0x0100 are capable of simultaneously allocating multiple protected-mode selectors in a single call. When that happens, both services return only the first ...
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How can a protected-mode Watcom C program access memory that a real-mode interrupt service returned in a segment:offset register pair?
I'm using Open Watcom 1.9 to write some 286 real mode, and 386 protected mode software for DOS in C.
In real mode, I can retrieve a pointer to the system ROM character bitmaps in real mode using int ...
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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 ...
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