------ Original Message ------
From: "Chris Albertson" <albertson.ch...@gmail.com>
To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
Sent: 7/28/2017 3:14:56 PM
Subject: Re: [Emc-users] [7x12minilathe] CNCZEUS is now Open source
Yes, still if you run Linux in single user mode it should behave like
DOS ...
No. Not at all like DOS, In Linux even running as root, system calls
are
still trapped and executed in the kernel on behalf of the user.
Memory
and file aches controls are in place the root user can start any number
of
tasks that are scheduled. Basically it's still Linux/Unix
Under DOS there is no kernel and nothing is trapped. All DOS does is
load
the app's image from disk and jump to it's entry point. Technically
DOS
is not even an operating system. All the functions of an OS have to
reside
in the user's application. Think of DOS is a fancy boot loader.
Prior to MS-DOS 7 (the DOS that Windows 95 launches from) the core
system functions of DOS were handled by IO.SYS and MSDOS.SYS while
filesystem handling and things like communicating with serial and
parallel ports via the drivers in IO.SYS and/or MSDOS.SYS were taken
care of by COMMAND.COM
With MS-DOS 7 the functions of MSDOS.SYS were combined into IO.SYS while
MSDOS.SYS became a plain text file holding information such as where to
launch Windows from, making it much easier to have two or more installs
of Windows on one PC.
The BIOS and various basic peripherals presented a standardized system
for DOS so no extra drivers were required to work with files, send text
to a monitor, access floppy and hard disk drives, standard ports, and
the basic graphics functions IBM had in the CGA, EGA and 640x480 VGA
standards. To use those graphics functions a DOS program had to be
written to access them but it didn't have to have any code beyond
activating the mode and throwing properly formatted data at the card.
The modes were (likely still are on most GPU cards) exactly the same on
every card. That's what standards are good for. :-)
DOS is far more than a 'fancy boot loader'.
What did cause problems were printers. Plain text could be sent to
serial or parallel printers by sending it directly to the port, without
any special formatting. Of course all you'd get on paper was plain,
unformatted text - and all stamped out over and over on one line if you
got the CR/LF switch settings wrong on the printer. That was usually
step one, finding out if the printer could be set to do its own linefeed
with every carriage return and setting up all your printing programs to
match.
Beyond that, any special functions of a printer had to be individually
part of every program that printed. I usually had two different printers
in my DOS and Windows 3.1x years because several DOS programs supported
one but not the other. Nobody ever bothered to invent anything like a
standardized high resolution and graphics interface that could be
supported by a loadable driver, accessible to any DOS program via simple
and tiny function calls.
Other hardware without support built into DOS eventually got that.
CD-ROMs eventually got a couple of nearly universal drivers so memory
could be saved by using a single driver to support two or more drives
from different manufacturers. PCMCIA cards got there for some types of
devices. Even tap backups eventually got around to some interface
standards for drives that connected to floppy controllers.
But printers? Nope. Never. Epson, HP, STAR, Qume, Cannon and the rest
never did get around to working together for DOS support. Windows forced
them to get along, for Windows programs, by requiring printer drivers to
'plug into' Windows' own higher level API so that every printing Windows
program could use Windows' interface instead of having to speak each
different printer brand's proprietary language.
PCMCIA didn't get much, if any, better with Win 3.1x. Still relied on
DOS drivers and could be a huge RAM hog if you had more than a couple of
devices that required point drivers instead of being able to use the
multiple device supporting class drivers.
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