Path: utzoo!attcan!uunet!isc-br!tau-ceti!cims2!proto!joe
From: joe@proto.COM (Joe Huffman)
Newsgroups: comp.lang.c++
Subject: Re: Zortech C++ Version 2.1
Summary: VCM is real mode fancy overlays, DOS extender is protected mode.
Message-ID: <1320@proto.COM>
Date: 28 Jun 90 19:58:54 GMT
References: <25252@unix.cis.pitt.edu>
Organization: Prototronics; Sandpoint, Idaho
Lines: 38

In article <25252@unix.cis.pitt.edu>, rozin@unix.cis.pitt.edu (R Rozin) writes:
> 
> I just received an upgrade order form from Zortech, for version 2.1. 
> Two of the advertised new features which seem unclear to me are:
> 
>     1. Virtual code manager, which is supposed to let you write programs
>        up to 4 megabytes in size in real mode.
> 
>     2. Rational systems Dos extender, which is supposed to let you write
>        proprams which access memory beyond 640k.
> 
> If you have 1., why would you need 2.?  Does anyone know more about these

There is some runtime overhead with the VCM, see 'Virtual Memory For 640K DOS'
by Walter Bright in the July 1990 issue of 'The C Users Journal'.  Depending
on your application it may be unacceptable.

> features?  Would they let you write programs whose data is about 2-3 mbytes,
> without worrying about expanded memory, and without using the __handle?

VCM doesn't overlay data, so the answer is no for VCM.  As for the Rational
Systems I believe the answer is as follows:  You can malloc (standard malloc,
not handle_malloc()) as many blocks of (up to 64K in size) memory as you want
until you run out of extended memory.  So the answer is yes if you can break
the data up into blocks of < 64k.

> How does it compare to the facility of Turbo C++ which provides virtual
> memory (in a way)?

VROOM?  Walter says (paraphrased and toned down from a private conversation) 
that VCM is better.  Of course he wrote it, so consider the potential for
bias.


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