SEGMENT          Initiate segment definition                        Directive

  SEGMENT name [attributes]             ; Ideal mode
  name SEGMENT [attributes]             ; MASM mode

    Most applications can use segments created using the standard memory
    models (defined with the MODEL directive). To get full control over
    all aspects of segment generation, the SEGMENT directive is required.

    The SEGMENT directive opens a segment. All code or data following it
    will be included in the segment, until a corresponding ENDS directive
    closes the segment. If you have already defined a segment with the
    same name, this segment is treated as a continuation of the previous
    one. You need only specify the segment attributes the first time you
    open the segment.


    Segment attributes are (TASM processes attribute values from left to
    right):

       - alignment attribute            tells the linker to ensure that
                                        a segment begins at a specified
                                        boundary
       - combination attribute          tells the linker how to combine
                                        segments from different modules
       - class attribute                helps the linker determine the
                                        order in which segments are to
                                        be ordered in the program file
                                        (e.g. separate code and data)
       - size attribute                 (≥80386) tells linker if segment
                                        is 16 or 32 bit
       - access attribute               tells linker to apply specific
                                        access restrictions to a segment
                                        (currently only supported by the
                                        Phar Lap linker)

    ──────────────────────────────────────────────────────────────────────

    align specifies the type of memory boundary where the segment must
    start: BYTE, WORD, DWORD, PARA (default, 16 bytes), PAGE (256 bytes),
    or MEMPAGE (4 KB).


    combine specifies how segments from different modules but with the same
    name will be combined at link time:

      AT expr       locates segment at absolute paragraph address expr
                    (typically used as a template, e.g for the BIOS data
                    area: SEGMENT bios_data AT 0040h); the linker emits no
                    code or data for AT segments
      COMMON        locates this segment and all other segments with the
                    same name at the same address (overlapping)
      MEMORY        (same as PUBLIC)
      PRIVATE       does not combine this segment with any other segments;
                    this is the default
      PUBLIC        concatenates all segments with the same name to form
                    a single contiguous segment
      STACK         concatenates all segments with the same name to form
                    a single contiguous segment, then initializes SS to the
                    beginning of the segment and SP to the length of the
                    segment
      VIRTUAL       defines a special kind of segment that will be treated
                    as a common area and attached to another segment at
                    link time (permits sharing of static data that comes
                    into many modules from included files)
      UNINIT        will cause TASM to warn if any data is written to the
                    segment (use with uninitialized data segments)
                    (e.g. SEGMENT udata2 PARA PUBLIC UNINIT "BSS")


    class controls the ordering of segments at link time: segments with the
    same class name are loaded into memory together, regardless of the order
    in which they appear in the source file.


    size specifies the default word size for the segment if 80386 code
    generation is enabled, and can be either USE16 or USE32.
 

    access

       EXECONLY    segment is executable only
       EXECREAD    segment is readable and executable
       READONLY    segment is readable only
       READWRITE   segment is readable and writable

    The Phar Lap linker assumes that the segment is meant to run in
    protected mode if you select any of these attributes, or if you select
    the USE32 attribute. TASM assumes the READONLY attribute if you
    selected the USE32 attribute but did not specify any of these four
    attributes.

    ──────────────────────────────────────────────────────────────────────

    Example showing mixed simplified and generic segmentation:

        ; File: i.inc
        ideal
        model   nearstack compact, nolanguage
        p186
        segment bmp_image para public uninit "FAR_BSS"
        ends
        segment vga_graphics at 0A000h
        ends

        ; File: imain.asm
        ideal
        include "i.inc"
        STACK   200h
        DATASEG
        fname   db "d:\bmp\352x200.bmp",0
        UFARDATA bmp_image                      ; Public segment
                buf_size = 0fff0h
        bmp_buffer db buf_size dup (?)
        UFARDATA pcx_image                      ; Private segment
        pcx_buffer db buf_size dup (?)
        CODESEG
        procdesc load_n_draw Pascal :dword, :word
        StartupCode
        call    load_n_draw Pascal, ds offset fname, buf_size
        ExitCode 0
        ;...
        END     @Startup