# Virtual drives/non-existent Drive letters under DOS? #

# Virtual drives/non-existent Drive letters under DOS? #

Post by Charles D » Sun, 30 Jun 1996 04:00:00




>Hi all.

>I asked this question a while ago, with little response. Can someone tell me
>how I can create a virtual disk drive under DOS? That is, how do I get DOS
>to think that a certain drive letter is assigned when it really isn't?

For a thorough discussion of phantom and non-DOS drives, get a copy of
"Undocumented DOS" by Schulman et al.  Chapter 8 covers the file system
in excruciating detail.  To anwer your question in brief, you can create non-
useful drives simply by setting bits in the drive's CDS entry.  If you want
the drive to actually do useful things, though, you need to start implementing
IFS functions -- and it rapidly becomes less simple!

The book is published by Addison-Wesley, and the ISBN number is
0-201-63287-X.


 
 
 

# Virtual drives/non-existent Drive letters under DOS? #

Post by Paul D. DeRocc » Sun, 30 Jun 1996 04:00:00



> I asked this question a while ago, with little response. Can someone tell me
> how I can create a virtual disk drive under DOS? That is, how do I get DOS
> to think that a certain drive letter is assigned when it really isn't?

If by "virtual disk drive" you mean the sort of virtual drive created by
the SUBST command, then it can be done. Under DOS 6-, you have to poke
into the current directory table, which is documented under Int 0x21
function 0x52 (SYSVARS) in Ralf Brown's Interrupt List. If you have
trouble understanding the description, the best thing to do is to write
a simple program that dumps this area, and see what you get for various
SUBST commands. Under DOS 7 (a.k.a. Windows 95), there is a new DOS
function call (0x71AA0 for manipulating the SUBST table, which is of
course much easier and safer.
--

Ciao,
Paul D. DeRocco

 
 
 

# Virtual drives/non-existent Drive letters under DOS? #

Post by Anton Maurovi » Mon, 01 Jul 1996 04:00:00


Hi all.

I asked this question a while ago, with little response. Can someone tell me
how I can create a virtual disk drive under DOS? That is, how do I get DOS
to think that a certain drive letter is assigned when it really isn't?

- Anton

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1. Swap CDROM drive letter with a hard-drive partition drive letter

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