Here's another thread where I expect Mark Larson could provide some useful help :)

For my toy kernel, I need to know what the memory map below the 1meg barrier is like... above 1meg I'll rely on int15 E820 if it's available, and if not either E801 or 88. That ought to be fairly trivial.

I have an old reference here that seems to say that basically memory from 0x500 to 0x9FFFF is available for my use and the rest are reserved for various things? Are there any other reserved areas that I should be aware of?
Posted on 2005-01-09 00:23:16 by f0dder
No, as long as your kernel doesn't use BIOS functions (int 05 print screen, called by the BIOS keyboard driver, uses a flag at 0:0500h for example)
Posted on 2005-01-09 03:42:19 by japheth
Hm, my reference says that 0x400-0x4FF is "Bios data" while 0x500-0x5FF is "DOS and system"... no that it matters that much, "my" memory map starts at 0x1000 :)
Posted on 2005-01-09 05:44:22 by f0dder
The first megabyte of memory (0000:0000 to 000F:FFFF)
Conventional (Base) Memory is from 0000:0000 to 0009:FFFF (first 640K)
Upper Memory is from 000A:0000 to 000F:FFFF (last 384K)

Conventional Memory Setup
0000:0000 to 0000:03FF - The Interrupt Vector Table for x86 Real Mode (the first kilo of memory)
0000:0400 to 0000:04FF - The BIOS Data Area
0000:7C00 to 0000:7DFF - MBR loaded by BIOS
-Everything else is free game for usage in Conventional Memory, just watch out for the stack.

Upper Memory Setup
000A:0000 to 000A:FFFF - Mapped RAM for Graphics Mode Video Cards
000B:0000 to 000B:7FFF - Mapped RAM for Monochrome Text
000B:8000 to 000B:FFFF - Mapped RAM for Color Text
000C:0000 to 000C:7FFF - Mapped ROM for Video
000C:8000 to 000D:FFFF - Mapped ROM for a Special Adapter
000E:0000 to 000F:FFFF - Mapped ROM for BIOS

Considerations
-If you ever plan on using Virtual 8086 mode, leave the IVT intact
Posted on 2005-01-09 09:31:54 by SpooK
Thanks, Spook - that map is mostly consistent with this (really old) map I have, except some of the ranges are described differently ("XT harddisk bios" and such). Just wanted to be sure the ranges I thought were free *are* indeed free :)

Yes, I plan on adding V86 sometime, and I'm not touching the first 4k at all.
Posted on 2005-01-10 08:54:18 by f0dder