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NDOS.TXT
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1993-05-30
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NDOS ?
by Chris Bieda
Why You Should Delete command.com
In the Beginning
Sooner or later, every victim of the MS-DOS and PC-DOS operating
systems comes to learn that there are three essential files that
compose the core of the systems. (In MS-DOS, these are msdos.sys,
io.sys and command.com; in PC-DOS, ibmdos.com, ibmbio.com and
command.com.) This knowledge usually is acquired shortly after the
user deletes command.com because it doesn't appear to do anything
useful, and besides, it's taking up disk space. (This is also the
point at which many users learn the expressions "bootable disk"
and "boot floppy.")
The undaunted few proceed beyond this sobering experience to learn
what command.com actually does: it supplies the interface, a command
line, to DOS, as well as provides certain fundamental utilities, like
copy and rename, and delete and "dir." (The fact that command.com
accepts what you type to the command prompt and decides how to
handle it, either by processing the command itself, or loading
another program to do so, is why it is referred to as "the," or more
properly, if rarely, "a" command processor or command interpreter.)
This ascension to the intermediate heights of power userdom is often
followed by the shocking revelation that command.com is, in fact, an
optional interface, at least insofar as you need not use command.com
if you have another command processor available!
(Just as an aside, if there is reading this an OS/2 user who is not
familiar with DOS, your cmd.exe serves the same purpose as DOS's
command.com, and it is just as optional!)
Command Processor Options
Besides DOS's command.com, there are two other options for command
processors that I know of (I would be glad to learn of others): the
JP Software company's 4DOS, a shareware program, and the Symantec
Corporation's NDOS. In fact, these two programs are extremely
similar, largely because NDOS is a licensed OEM version of an
earlier release of 4DOS! NDOS is supplied with version 6.xx of The
Norton Utilities, for many the indispensable set of DOS utilities,
and corresponds roughly to version 3.02 of 4DOS, which is currently
at version 4.01d.
Since many of us own The Norton Utilities, and many more should,
I will describe cool features of NDOS throughout this series. You
should note, however, that virtually everything I describe works
precisely the same way in the newer 4DOS , and if you don't own the
Norton package, you can attain the same level of functionality by
using 4DOS (which is available from our BBS service, as well as our
public domain and shareware library service, Public Brand Software).
By the end of my tour, I suspect that quite a few of you will delete
command.com one last time, because these optional processors are
great!
Compatibility Considerations
Probably the coolest feature of NDOS is that it is fabulously
compatible. In fact, since booting to it for the first time over a
year ago, I haven't found a single application or utility, or DOS
routine, that gags or runs differently.
This is no small feat, since there are literally dozens of books out
there with titles like Undocumented DOS or Secrets of the Command
Line Bill Gates Doesn't Want You To Know. DOS, like any complex
operation (it is a system, after all), is full of bugs, leftover
code (with leftover unintentional results) and back and trapdoors,
as well as undocumented or unsupported features. To successfully
support Windows 3.x, DESQview, and some of the worst-written TSR's
(terminate and stay resident, or "pop up," programs) ever, which were
written for command.com exclusively, NDOS must mimic the basic
operations of command.com almost perfectly. Based on my experience,
it does.
Installation
A lesson many support personnel learn, often by painful trial and
error, is to get command.com tucked safely away in some place
that del-happy tyros won't easily find it (this is called "making
your life easier"). The traditional remedy has been to copy
command.com to a subdirectory, say the c:\dos subdirectory, and to
add the following line to the config.sys file in the root directory:
shell=c:\dos\command.com c:\dos /p
which instructs DOS to look for command.com in the specified
subdirectory at bootup, to look for a copy of command.com in c:\dos
when (if) it needs to load another, and (the "/p" part) to leave
DOS running that particular processor ( c:\dos\command.com )
when the bootup procedure is done. (It will also cause
c:\autoexec.bat to be run, which is most often a good thing!)
Once these modifications were made (and with a bootable floppy at
the ready), c:\command.com was deleted, and the system rebooted
to look for, and use, the command.com tucked away. This often
solved the problem of del -zeal. (It remains recommended.)
This same method is used to call NDOS instead of command.com,
to wit:
shell=c:\norton\ndos.com c:\norton /p
So much for installation.
Making It All Pretty
For real DOS-jockeys, the command-line, and not some fancy menuing
interface like Windows, GeoWorks or even XTree, is the only way to
fly; it's certainly quicker, and "doing" the command-line marks you
as a real pro. It's what separates the adults from, say, Macintosh
users (just kidding folks). And for these people, the appearance of
their beloved DOS "prompt" (the onscreen "message" displayed while
DOS awaits your next command) is critical. It must be useful, perhaps
fanciful, but certainly unique.
Probably 95% of all DOS systems have a prompt that looks like "A" or
"C" or "A:\" or "C:\". While these are useful (surely the latter
pair more than the former), they are not fanciful, nor unique.
command.com gives you a handful of prompt customization options, but
NDOS supplies more, including perhaps the coolest prompt
feature imaginable, the (jargon-alert!) "shell nesting level."
Back up a moment. The "shell," as you might have gathered by now, is
the context in which DOS software (applications and utilities) are
run. It is established and maintained by the command processor
(whether command.com or NDOS), and a single context (instance of the
shell) is often all that a user, particularly one who works solely
within single applications (like 1-2-3 or WordPerfect) requires.
Many users, however, use and enjoy a feature supplied by many
applications, commonly referred to as "shelling to DOS," or "opening
a DOS shell." These functions give the appearance of temporarily
exiting the application and returning to a point immediately before
the application was loaded, when the user was staring at a DOS prompt.
In fact, this is an illusion. Far from exiting the application,
opening up a shell from within it temporarily suspends the
processing of that application (disconnecting it, as it were, from
the keyboard, display, disk drives, etc.), and opens up another
application: the command processor.
You see, whether you are using command.com, ndos. com or 4dos.com,
you are already running a program (hence the ".com" for a command
file), which is a command processor, or "shell." When you load
1-2-3 into that shell, you have now loaded two programs, the
second beneath the first. When you use that second program's
ability to "shell" to DOS, you open a third program (another shell),
and while in that second shell, you may even open a fourth, such as
a small utility program. God help you if that fourth program also
allows shelling to DOS (if you're keeping count, number five),
for if you do so, you may well get lost in your shells! This is
hazardous in the extreme when using command.com-based shells, for t
here is no simple way to tell if you are at the bottom of the "stack:"
all the shells (command lines) look alike! (Several applications
modify the prompt in the shells they spawn, to help clue you in,
e.g., "Type "exit" to return to WordStar.;" many simply do not.)
Should you shut your computer off (or should it lock up) while in a
"nested" (number two or subsequent) shell, all your work in the
applications resting below that was not saved before you went
shelling will be lost. Scary stuff.
NDOS enables a delightful prompt modification that can permanently
save your bacon. Putting the lowercase letter z into your prompt
string will imply the number of shells you have invoked by
displaying the sequence number of the one you are currently in,
starting with "0" (zero) for the first. So, for example:
prompt Level z [$p$g]
will return a prompt of "Level 0 [C:\]" when you are in the first
(primary) shell, "Level 1 [C:\]" when in the second, and so on. As a
result, when you are at any NDOS prompt, you know if there remain
matters beneath the current shell that require your attention. (At
Level 0, there is not; at other Levels, there are.) This is, of
course, no help whatever when the computer locks up in a secondary
or tertiary (or . . . ) shell, but when you are in control, you are
never blind.
To be perfectly honest, so much do I use shells, and so few of these
shells provide customized prompts by themselves, that this one cool
feature would warrant my use of NDOS over command.com.
But there's more to NDOS than this, like faster batch file
processing, interactive batch files, and a doskey facility that
allows you to customize your environment to an amazing extent while
saving RAM!