Hi..
 > Lesson 1:
 > In Real mode, the 80x86 can access up yo 1,024KB of memory using
 > segments and offsets. An offset is a 16-bit logical address used to
 > reference bytes within a segment. The first byte in a segment is at
 > offset 0000, the second is at 0001 and so on (The last is at FFFF).
Correction to lesson one: in real mode, the 286+ can access 1088kb-16 bytes 
of memory. This is achieved by segmentreg=FFFFh offset reg=0 to FFFFh. This 
is how the 286+ ITSELF operates.
Now, hardware incorporated in the **specific design** of the IBM-PC 
effectively
disables this feature whilst in real mode. This specifc hardware is called 
he
A20 Gate. This feature was included so that the design would remain 100% 
software compatable with the older, 8086 based design. The fact that you only
program on a PC whose hardware design limits you to 1024kb whilst in real 
ode
does not subtract from the fact that the 286+ it's self does NOT have this
limitation.
Finally, you can switch on the A20 gate yourelf if you like and restore the
full addresability - you just need to know how to program the hardware, or, 
in this day and age, ask Himem.sys to do it for you.
 > The 286 (technically referred to as the 80286)
 > processor was the first in the Intel family to introduce separate
 > operating modes. The architectural features of Protected Mode included
 > larger physical memory, better memory management, and hardware support
 > for multi-tasking and task-switching operations.
AFAIK the 80386 was the first processor to introduce hardware support for 
multi-tasking and task-switching. Care to say how the '286 implements this 
so-called 'hardware support'?
    Craig
--- FMail/386 1.20+
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