"IBM personal computer assembly language tutorial" - читать интересную книгу автора (Auerbach J.)

complex options such as the GROUP statement and the use of other "combine
types" and "classes." I don't recommend getting into any of that. I will
talk more about the linker and modular construction of programs a little
later. The assembler manual also implies that a STACK segment is required.
This is not really true. There are numerous ways to assure that you have a
valid stack at execution time.

Of course, if you plan to write applications in assembler which are more
than 64K in size, you will need more than what I have told you; but who is
really going to do that? Any application that large is likely to be coded
in a higher level language.

The third form of the SEGMENT statement makes the delineated section into
something like a "DSECT;" that is, it doesn't generate any code, it just
describes what is present somewhere already in the computer's memory.
Sometimes the AT value you give is meaningful. For example, the BIOS work
area is located at location 40 hex. So, you might see

BIOSAREA SEGMENT AT 40H ;Map BIOS work area
ORG BIOSAREA+10H
EQUIP DB ? ;Location of equipment flags, first byte
BIOSAREA ENDS

in a program which was interested in mucking around in the BIOS work area.

At other times, the AT value you give may be arbitrary, as when you are
mapping a repeated control block:


IBM PC Assembly Language Tutorial 18


PROGPREF SEGMENT AT 0 ;Really a DSECT mapping the program prefix
ORG PROGPREF+6
MEMSIZE DW ? ;Size of available memory
PROGPREF ENDS

Really, no matter whether the AT value represents truth or fiction, it is
your responsibility, not the assembler's, to get set up a segment register
so that you can really reach the storage in question. So, you can't say

MOV AL,EQUIP

unless you first say something like

MOV AX,BIOSAREA ;BIOSAREA becomes a symbol with value 40H
MOV ES,AX
ASSUME ES:BIOSAREA

Enough about SEGMENT. The END statement is simple. It goes at the end of