OSDev.org

Hi,

AFAIK this ISA memory hole only relates to ISA video cards. Theoreticaly, there can be a hole anywhere in memory. For example, device configuration space tends to be in high memory but needn't be. There may be an APIC hiding up there somewhere in high memory too.

As long as you're creating your physical memory allocator based on int 15h, AX=E820h, you should be fine. If you can't use this function, assume worst case scenario - i.e. a memory hole at 15Mb and a large PCI configuration space in high memory.

Cheers,
Adam

ouchouchouch, your OS would seriously bork my test box when it finds the video memory (located at 1G) and think it's RAM...

I used INT 15h E801, so people with less memory are okay. i should probably upgrade to the E820 call.

It returns a value just shy of 2 Gig=0x80000000. I have no clue what's just below the 2 Gig mark -- something tiny.

Umm... The IHC7 chip uses stuff in the 0xFE000000 range. I have a video card in the 0xE0000000. In general the 0x80000000-0xFFFFFFFF range seems full of landmines

Currently you must enter physical address ranges of additional RAM beyond 2 Gig when you compile the kernel. I only have 2 Gig and have no idea where a third or fourth Gig would be mapped. My OS is 64-bit, so I can handle more memory. You know... the problem of only having one or two machines to test on really sucks when it comes to operating systems. Actually, it's a convenient excuse

You should DEFINITELY use E820 if you can. Any newer system has it. There's some information in this topic that might be useful when using E820, as there are some catches.