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From: dmt@mtunb.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: IBM new 'standard'
Message-ID: <890@mtunb.UUCP>
Date: Wed, 1-Apr-87 08:01:33 EST
Article-I.D.: mtunb.890
Posted: Wed Apr  1 08:01:33 1987
Date-Received: Sat, 4-Apr-87 08:53:42 EST
References: <701@imsvax.UUCP> <855@bucsb.bu.edu.UUCP> <882@mtunb.UUCP> <1353@steinmetz.steinmetz.UUCP>
Reply-To: dmt@mtunb.UUCP (Dave Tutelman)
Organization: AT&T Information Systems - Lincroft, NJ
Lines: 40

In article <1353@steinmetz.steinmetz.UUCP> davidsen@kbsvax.steinmetz.UUCP (William E. Davidsen Jr) writes:
>
>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.
>... [ definitions of 4 classes ]

I like your classes.

>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.

OK, here are a few things that "Class 4 ill-behaved" programs (the
***REAL UGLIES*** in your classification) do all the time:

   -	If you buy the performance need for writing to display RAM, then
	remember that moving the cursor requires I/O to a 6845 register.

   -	The serial port BIOS calls are so brain-damaged as to be useless
	at more than 300 baud.  Every communications program I've seen for
	MSDOS machines have their own I/O interface to the serial port.
	(Editorial comment - this is not a BIOS implementation problem;
	it's an architectural screw-up.  There's no non-blocking READ
	in the BIOS.)

   -	There is no BIOS or DOS function to access the speaker port.
	If you want to do anything more than a standard "beep"
	(putc (7) ), you've got to do explicit OUTs.

There are others, but these are probably the most common.

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