ASSUME           Associate segment with segment register            Directive

  ASSUME segreg:expression [,segreg:expression] ...
  ASSUME NOTHING

    Specifies the segment register (segreg) that will be used to calculate
    the effective addresses for all labels and variables defined under a
    given segment or group name.

    expression is one of the following:
       - the name of a group as defined with the GROUP directive
       - the name of a segment as defined with the SEGMENT directive or
         one of the simplified segmentation directives
       - an expression using the SEG operator
       - the keyword NOTHING

    The NOTHING keyword cancels the association between the designated
    segment register and segment or group name. The ASSUME NOTHING
    statement removes all associations between segment registers and
    segment or group names.

    You can use the ASSUME directive whenever you modify a segment register,
    or at the start of a procedure to specify the assumptions at that point.
    If you use a MODEL statement, Turbo Assembler automatically sets up the
    initial ASSUMEs for you.