hi. i have some question about memory addressing:
-in protected mode, is the segment base address (in descriptors) only for protection (to sign the begining of a segment), or that used to calculate the memory ( i mean that the physical address will be the offset ([ebx] for example) plus the segment base address).

-how descriptor cashes used in real mode (on new processors)? i mean, that are they only for protection, to controll the operand and address size and such, or not ( i guess yes)?

segment base address is also used to count final address. so final address is segment base address + offset.

segment limit still works under real mode, segment base is ignored, 32/16bit code works (but interrupt still push only 16bit IP on stack), don't know about others.

ok thank you!

Just one more thing:

[quote="vid"](but interrupt still push only 16bit IP on stack), don't know about others.[/quote]

Is that mean, that even hardware interrupts (i guess)? so if i hit a key on the keyboard, it will push only 16 bit offset when interrupt?

yes... no way to place code above 1MB

Another questions:
-can i use address and operand size prefix in real mode?
-You mean no way to place code above 1mb if i want interrupts to work correctly or you meant that no way to hold the cs descriptor cache (will it updated anyway?).

- yes, use can use prefixes.
- you can't. Not because cached CS - that stays unchanged. It is because offset pushed is 16 bit even if code is 32bit.

thanks!