Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 21h Function 24h
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     This function is used when switching from sequential to random I/O
     within a file. The contents of the relative-record field (offset
     21h) are derived from the record size (offset 0Eh), current block
     (offset 0Ch), and current record (offset 20h) fields of the file
     control block.
 
     All four bytes of the FCB relative-record field (offset 21h)
     should be initialized to zero before calling this function.
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