Addressing modes

I was wondering if anyone could clear up, a very simple issue for me. How
are the various segment registers applicable in 32-bit (i.e. non 16-bit)
code? Do the addresses simply get translated into 32 bit values and then
used as a immediate 32 bit value ? Thanks for any information.

"Daniel Huw Bellringer" wrote in
message ...
I was wondering if anyone could clear up, a very simple issue for me. How
are the various segment registers applicable in 32-bit (i.e. non 16-bit)
code? Do the addresses simply get translated into 32 bit values and then
used as a immediate 32 bit value ? Thanks for any information.

Those segments are all still there in 32-bit mode, but they are extremely
flexible in how they are defined, and most operating systems simply define
them to be equal to zero, in a way, so they can ignore them.

But you can conceivably have 48-bit addresses in an x86 32-bit processor
using segments. That is 16:32 for segmentffset. Each segment could be a
defined 4GB address area. Of course, most of that wouldn't fit in physical
memory, so it would have to be obtained through virtual memory.

Yousuf Khan

"Yousuf Khan" wrote in message
ble.rogers.com...

(snip)

Those segments are all still there in 32-bit mode, but they are extremely
flexible in how they are defined, and most operating systems simply define
them to be equal to zero, in a way, so they can ignore them.

But you can conceivably have 48-bit addresses in an x86 32-bit processor
using segments. That is 16:32 for segmentffset. Each segment could be a
defined 4GB address area. Of course, most of that wouldn't fit in physical
memory, so it would have to be obtained through virtual memory.

You could have 64GB physical memory, but only 4GB can be mapped by the MMU
at once.

No OS that I know of will do the remapping to allow multiple segments and
4GB addressable real memory for one task.

-- glen

"Glen Herrmannsfeldt" wrote in message
news:1m87b.395855$Ho3.59305@sccrnsc03...
But you can conceivably have 48-bit addresses in an x86 32-bit processor
using segments. That is 16:32 for segmentffset. Each segment could be
a
defined 4GB address area. Of course, most of that wouldn't fit in
physical
memory, so it would have to be obtained through virtual memory.

You could have 64GB physical memory, but only 4GB can be mapped by the MMU
at once.

No OS that I know of will do the remapping to allow multiple segments and
4GB addressable real memory for one task.

Yes, exactly.

Yousuf Khan