On Sat, 20 Sep 2014, Ali wrote:
That would be great. As Fred mentioned in another post
the system maybe
MS DOS compatible but not PC compatible. Although, I was always under
the impression it was the other way around i.e. MS DOS compatibility was
a subset of PC Compatibility i.e. a PC could run multiple DOSes (e.g.
MS-DOS, PC-DOS, DR-ROS, CP/M, Netware, etc.) but MS-DOS could only be
run on a PC...
An interesting way to look at it.
ALL "PC-Compatible" machines can run PC-DOS, which [<5.00]is a version of
MS-DOS.
Almost all MS-DOS machines can run PC-DOS. But more importantly, to be
"PC-Compatible", it must run not only the OS, but also the software
written for the PC. MOST commercial software did not use the operating
system for input and output. Putting bytes into video memory is MUCH
faster then asking the operating system to write a character, which then
asks the BIOS to write a character, which then puts the byte into video
memory. If you are filling the entire screen with text, that will look
like a teletype, whereas REP MOVSW can write those 2000 characters (AND
attributes) in way less time (not much more than 1/30 second)
BIOS provides much more versatile keyboard input - get a character and
echo it, get a character without echoing, and very importantly, check for
a character and get it WITHOUT waiting until there is a character before
coming back.
Using the OS for disk IO works great for files. It's possible, but
awkward, to read or write sectors. It is not practical to read or write
sectors that are a different size than what that version of the OS is
configured for.
MS-DOS itself is a moderately portable system.
It can be used on machines without video memory in the same place as the
PC, or even on machines that do their console IO without video memory.
It doesn't CARE what the video, keyboard, or FDC hardware is. But that
means that it also can only do what it is designed for. PC-DOS is MS-DOS
configured for the IBM PC. NEC MS-DOS is MS-DOS configured for the NEC.
So, therefore, since PC-DOS is a version (or "subset") of MS-DOS,
"PC-Compatible" is a "subset" of MS-DOS compatible, and can include
some machines with different hardware.
At a trivial level, that could mean that there could be a machine that is
not "PC compatible" that is very similar, or even identical, except for
for example, using a different kind of disk drive. DEC Rainbow, Victor
9000, Gavilan, Toshiba T300, etc. all run various versions of MS-DOS, but
commercial PC software will not run on them.
--
Grumpy Ol' Fred cisin at
xenosoft.com