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From: cliffhanger@cup.portal.com (Cliff C Heyer)
Newsgroups: comp.sys.ibm.pc
Subject: int 13h vs. int 21h disk I/O confusion
Message-ID: <26038@cup.portal.com>
Date: 17 Jan 90 15:11:27 GMT
Organization: The Portal System (TM)
Lines: 31

Books explain int 21h calls as being more 
functional and portable than int 13h calls.
But I'm wondering if there other important
benefits of one method vs. the other.

A point of confusion is what do compilers
output. The C compiler gives you a choice of
what to use, but I assume other languages
may use either 13h or 21h when you compile
a program, and you might not know which one
is used(?) Also 21h gives more than one
way of doing disk I/O (FCBs, Fcn. 44 &
_dos_ interface calls). Do you use switches
to control which is used in some languages?

Further, books say 13h is for floppies only.
If you write a program using 13h, does it
crash if you try it on a hard disk? Does
the compiler generate code that detects
a hard disk and and substitute 21h
calls?

Also, do 13h and 21h access installed device
drivers the same way, or does 13h speak
the WD1003 interface language only and
bypass any installed device drivers.

Perhaps I have not found the right book that
really explains all this stuff.

Cliff