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From: davidsen@steinmetz.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: IBM new 'standard'
Message-ID: <1353@steinmetz.steinmetz.UUCP>
Date: Mon, 30-Mar-87 14:07:19 EST
Article-I.D.: steinmet.1353
Posted: Mon Mar 30 14:07:19 1987
Date-Received: Wed, 1-Apr-87 06:45:56 EST
References: <701@imsvax.UUCP> <855@bucsb.bu.edu.UUCP> <882@mtunb.UUCP>
Reply-To: davidsen@kbsvax.steinmetz.UUCP (William E. Davidsen Jr)
Organization: General Electric CRD, Schenectady, NY
Lines: 34


There have been several postings about "well behaved" and "ill behaved"
program. I would like to offer a suggestion for classifying these
programs, in order to clarify what problems are caused by each.

Class 1: "well behaved" - performs all i/o via calls to the BDOS and
assumes nothing about memory outside its own program space. Example:
Microsoft C.

Class 2: "Reasonably well behaved" - performs all its i/o via calls to
the BDOS or BIOS. Does not use memory outside its own program space.

Class 3: "direct screen writes" - performs all i/o except screen write
(or reads) by calls to the BDOS or BIOS. Does not issue any IN or OUT
instructions. Does not use any memory except the screen memory and its
own program space.

Class 4: "ill behaved" - issues any IN or OUT instructions, writes in
system memory, reads data from the tables at the start of the BDOS, etc.
----------------------------------------------------------------
Having defined my terms, I believe that class 1, 2, and 3 programs will
run on IBM's new hardware, class 4 will not.

I have often wonderd why people diddle i/o ports directly. Going
directly to the screen memory is obviously a big performance win (as is
using int 29h to write to the screen driver), but hopefully no one is
changing the screen mode or the serial baudrates, etc, often enough to
need the performance of direct i/o.

-- 
bill davidsen			sixhub \
      ihnp4!seismo!rochester!steinmetz ->  crdos1!davidsen
				chinet /
ARPA: davidsen%crdos1.uucp@ge-crd.ARPA (or davidsen@ge-crd.ARPA)