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From: brownc@utah-cs.UUCP (Eric C. Brown)
Newsgroups: net.arch
Subject: Re: What if IBM Had chosen the 68000?
Message-ID: <3557@utah-cs.UUCP>
Date: Fri, 22-Nov-85 11:37:21 EST
Article-I.D.: utah-cs.3557
Posted: Fri Nov 22 11:37:21 1985
Date-Received: Sun, 24-Nov-85 05:32:43 EST
References: <129@intelca.UUCP> <392@aum.UUCP> <225@l5.uucp>
Reply-To: brownc@utah-cs.UUCP (Eric C. Brown)
Organization: Univ of Utah CS Dept
Lines: 31

In article <768@h-sc1.UUCP> thau@h-sc1.UUCP (robert thau) writes:
>> 2) CP/M Software (8080) is given no place to migrate.  CP/M programs and
>>    6502 programs all have a high degree of processor loyalty that C programs
>>    for 16 bit CPU's don't.  What this means
>>    is that CP/M doesn't die, and maintains strength the same way the Apple
>>    ][ and Commodore Architectures hang on.  
>WRONG.  Even the 8086 gave CP/M software no place to migrate.  It is true that
>the register set-up is similar to that of the 8080.  However, the instruction
>sets are not in one-to-one correspondance.  I recall a BYTE article several
>years back which compared a few 8080-to-8086 translators which were on the
>market at the time; all of them had to expand one instruction to three in some
>cases, and many could be tricked into far worse.  There were the inevitable
>problems with translation of operating system calls.  Lastly, any directly
>translated software would be unable to use more than 64K bytes.
>

Actually, the software *did* migrate; Microsoft Basic and early WordStar
versions for the IBM PC were nothing more than (poorly) translated copies of
8080 Microsoft Basic and WordStar.  Try unassembling IBM Cassette Basic or
Wordstar 3.0 or so.  As far as the OS call translation problems, MS-DOS 1.0
was essentially CP/M 2.2 with a different file structure.  The majority of
programs that did nothing but open, close, read, and write text files could
be ported without any major changes.  On your final point, you are correct,
most translated software didn't use more than 64K.  WordStar simply swapped
back and forth within its buffer of 20K or so, regardless of how much memory
was actually there.  That's why RAMDisks were so popular; if you couldn't
get at more than 64K above DOS, it made sense to load the rest of the stuff
into RAM and use it as a disk.

Eric C. Brown
brownc@utah-cs