Q30500

layout	title	permalink
page	Q30500: Segment Relative Versus Group Relative	/pubs/pc/reference/microsoft/kb/Q30500/

Q30500: Segment Relative Versus Group Relative

Article: Q30500
Version(s): 5.10
Operating System: MS-DOS
Flags: ENDUSER |
Last Modified: 23-MAY-1988

The following sample code will be used to explain segment relative
and group relative:

dgroup  GROUP   aseg,cseg
ASSUME  cs:dgroup,ds:dgroup
aseg    SEGMENT public  byte    'CODE'
        org 100h
        start:
        data_pointer    dw  the_data
aseg    ends
cseg    SEGMENT public  byte    'CODE'
        the_data    label   byte
cseg    ends
        end start

   When defining data, fixups are relative to the start of the
segment. The variable data_pointer will have an address relative to
the start of the aseg segment. If you want the variable to have an
address relative to the start of the group, you can explicitly state
the offset relative to dgroup as follows.

data_pointer    dw  offset  dgroup:the_data

   The exception is when you are using simplified segment directives.
In that case, group relative fixups always are used rather than
segment relative.
   In code segments, fixups are relative to either segment or group
depending on the ASSUME statements. In other words, the ASSUME
STATEMENT is checked before the fixup is generated. The exception here
is the same as above. When using simplified segment directives, group
relative fixups are the default.

   The OFFSET operator is segment relative and is discussed further in
a separate article.