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Q34985: PRB: A2102 Warnings Generated for Possible 80286 Problems

Article: Q34985
Product(s): Microsoft Macro Assembler
Version(s): 5.1
Operating System(s): 
Keyword(s): 
Last Modified: 04-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), version 5.1 
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SYMPTOMS
========

The Microsoft Macro Assembler (MASM) versions 5.1 and 5.1a will generate a
warning for the following sample code, while MASM version 6.0, 6.0a, and 6.0b
will assemble it without error. The warning generated by 5.1 and 5.1a is as
follows

  A4102: segment near (or at) 64K limit

The linkers that shipped with both products (versions 3.64 and 5.13,
respectively) will report the following error at link time

  L4020: code-segment size exceeds 64K-36

CAUSE
=====

Warnings are generated because code segments in the range of 65,501 - 65,536
bytes may be unreliable on certain 80286 processors.

MORE INFORMATION
================

The size of a 16-bit segment is limited to 64K. The recommendation of having
segments no larger than 65,500 (64K-36) is to avoid problems with certain 80286
processors.

When the segment really does exceed 64K, MASM 5.1 and 5.1a generate an error
rather than a warning

  A2102: segment near (or at) 64K limit

and MASM 6.0, 6.0a, 6.0b generates an error as well

  A2103: segment exceeds 64K limit

The following sample code will cause MASM to generate warnings, since the segment
size is between 65,501 and 65,536 bytes. Increasing the size of 'value' to
65,550 will result in errors rather than warnings.

Sample Code
-----------

  ; Assemble options needed: none

  .model small,c
  .286

  .stack
  .code

  start:

      MOV ax, @data
      MOV ds, ax

      value db 65500 dup ( ? )

      MOV ah, 4ch
      INT 21h

      END start

Additional query words: 5.10

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510
Version           : :5.1

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