Segmentation memory- question

[szarek]

Brendan, thanks for your help

The CPU has 2 different "spaces"

1. Therefore, is it phisically placed in cpu's memory?
2. Is it cache memory?
Thanks in advance

[Peterbjornx]

It is neither, IO space is address space mapped directly to peripheral registers, on a real 8086 an IO cycle would have a line asserted to signal that it was addressing IO and not memory, the IO device would then either latch the value on the bus or put its data on the bus depending on the kind of cycle(read,write)

[azblue]

the segment's limit is only "byte granular" if the segment is 64 KiB or less (for larger segments you have "4 KiB granular");

Isn't it possible to have 1MB data segments? Not that that would be particularly useful, but the CPU does support that, doesn't it?

[Brendan]

Hi,

the segment's limit is only "byte granular" if the segment is 64 KiB or less (for larger segments you have "4 KiB granular");

Isn't it possible to have 1MB data segments? Not that that would be particularly useful, but the CPU does support that, doesn't it?

You're right - it's "byte granular" up to 1 MiB (and 4 KiB granularity for 1 MiB or larger segments). Basically, you can set the limit to 0x000FFFFF (1 MiB - 1 byte), but can't set it to 0x00100001 (1 MiB + 1 byte) and would have to use a limit of 0x00101000 (1 MiB + 4 KiB) instead.


Cheers,

Brendan