What Is the Z: Drive in DOSBox? In Plain Words

What Z: is, in the documents’ own substance

The DOSBoxWiki ZDrive page says: “When DOSBox loads it automatically creates a Virtual Internal Drive called Z: which contains various utilities that make a reasonable approximation of a fully setup DOS Compatible environment.”

The wiki’s MOUNT page says the same thing from the other side. When you enter the command MOUNT from the DOSBox Z:\> prompt, the list it shows includes this line: “Drive Z is mounted as Internal Virtual Drive.”

The wiki’s Drives page calls it “a virtual drive in memory (RAMDrive) where the OS Tools are stored.” In plain words — this page’s own wording, not a quote — Z: is a drive DOSBox carries inside itself for its own tools, not a folder on your real computer that the documents point you to.

Why you start on Z:\>

The Manual says: “At the beginning you’ve got a Z:\> instead of a C:\> at the prompt.”

The Drives page says the same thing in its own words: in MS-DOS, users would commonly be greeted with a C:\> prompt once a computer was done booting, but “upon starting DOSBox the prompt instead reads Z:\>.”

The Manual’s next point explains why there is no C: yet: “You have to make your directories available as drives in DOSBox by using the ‘mount’ command.” The Manual’s Quickstart puts it this way: “DOSBox does not automatically make any drive (or a part of it) accessible to the emulation.”

What is on the Z: drive

The ZDrive page says, “You can find the following files in Z: drive,” and then lists:

• COMMAND.COM
• AUTOEXEC.BAT
• INTRO.COM
• KEYB.COM
• IMGMOUNT.COM
• BOOT.COM
• RESCAN.COM
• LOADFIX.COM
• MEM.COM
• MOUNT.COM
• MIXER.COM
• CONFIG.COM

That list is the ZDrive page’s list, in its order. The Manual covers programs with names matching several of those files in its section 4, “Internal Programs.” It says: “DOSBox supports most of the DOS commands found in command.com. To get a list of the internal commands type ‘HELP’ at the prompt. In addition, the following commands are available” — and then describes MOUNT, MEM, VER, CONFIG, LOADFIX, RESCAN, MIXER, IMGMOUNT, BOOT, IPX and KEYB.

The wiki’s Commands page gives one-line descriptions for many of the same names. For example, it describes CONFIG as “Change or query various DOSBox settings during runtime,” MEM as “A program to display the amount of free memory,” and MOUNT & IMGMOUNT as “Mount folders and CD-ROM drives.”

Why the Z: drive is at the front of the PATH

The ZDrive page says: “This drive is automatically inserted to the front of the PATH and cannot be modified.”

The wiki’s PATH page explains what that means. It says the PATH “is an environment variable that instructs DOSBox where to find an executable if one cannot be found in the current directory,” it gives the example “PATH=Z:\;C:\UTILITIES;C:\DOS,” and it says: “By default the Z:\ is at the beginning of the PATH making the default DOSBox utilities available to you no matter what sub directory you are currently in.”

One caution from the wiki itself: the MOUNT page separately says, “By default, the MOUNT command will not be recognized at the C:\> prompt.” This page prints both wiki statements exactly as they stand and does not try to reconcile them. If MOUNT does not answer where you are, the documents’ own examples show MOUNT being run from the Z:\> prompt.

Which drive letters are for your own drives

MOUNT is the program the documents give you for your own folders. The Manual describes it as a “Program to mount local directories as drives inside DOSBox,” and says: “Basically MOUNT allows you to connect real hardware to DOSBox’s emulated PC. So MOUNT C C:\GAMES tells DOSBox to use your C:\GAMES directory as drive C: in DOSBox.”

The wiki’s MOUNT page gives the basic template as “MOUNT [Drive-Letter] [Local-Directory],” and its usage examples mount a folder as C:, a floppy as A:, a CD-ROM as D:, and an image as E:. None of its examples mounts Z:.

The Manual also gives this guidance, in its own words: “HardDisk should always be mounted as c”; “CD-ROM should always be mounted as d”; “Floppy should always be mounted as a (or b).”

The Manual’s command-line section gives one further example of a different letter in use: an example that “mounts H:\MyFolder as the Y drive.”

So, in the documents’ own examples and guidance — this sentence is this page’s plain-words summary, not a quote — Z: is DOSBox’s, and the letters shown for a user’s own mounts are the likes of A:, C:, D:, E: and Y:. The documents read for this page do not print a complete list saying every other letter is free.

Why games and settings guides keep referring to Z:

First, because that is where the work starts. The wiki’s Basic Setup guide shows its running-a-game steps starting from the Z:\> prompt — for example, “Z:\>MOUNT C C:\OLDGAMES” — and then changing to the new drive by typing the drive letter, as in “Z:\>C:” followed by “C:\>.”

Second, because a settings program lives there. The Manual says, twice, in sections 13 and 14: “CONFIG.COM, which can be found on the internal DOSBox Z: drive when you start up DOSBox.” In section 13 the full sentence is that an extra configuration file “can be generated by CONFIG.COM, which can be found on the internal DOSBox Z: drive when you start up DOSBox.” In section 14 it says a language file can be generated the same way.

Third, because the startup tour lives there too. The Manual’s Quickstart says: “Type INTRO in DOSBox for a quick tour,” and INTRO.COM is one of the files the ZDrive page lists on Z:.

Can you use Z: for your own mount, or write to it?

On writing, the documents are direct. The Drives page says: “Users cannot write data to the Z:\ and it exists only for DOSBox purposes.” The ZDrive page says the drive “cannot be modified.”

On removing it, the Manual is also direct. Its description of MOUNT’s -u option, which it describes as “Removes the mount,” adds: “Doesn’t work for Z:\.”

On mounting your own folder as Z:, the documents read for this page are silent in a specific way, and this page will not fill the silence in. No example in the Manual or in the wiki’s MOUNT page mounts Z:, the MOUNT listing already shows Z: as the Internal Virtual Drive, and no anchor read for this page gives an error message or a step-by-step result for trying “MOUNT Z” with your own folder. What the documents do say is the part above: Z: is already DOSBox’s internal drive, it cannot be modified, users cannot write data to it, and unmounting does not work for it.

On hiding it, the ZDrive page says only this: “This Z: Drive can be largely hidden with some creative modifications to the AUTOEXEC.BAT for a more complete emulation of MS-DOS.” The page does not give those modifications, and this page does not invent them.

The difference, in one look

• Z: DOSBox’s Virtual Internal Drive, automatically created when DOSBox loads, holding DOSBox’s utilities, at the front of the PATH, and not modifiable.
• C:, and the other letters in the examples: drives you create with MOUNT, connecting a real directory or drive to DOSBox’s emulated PC — the Manual’s guidance is hard disk as C:, CD-ROM as D:, and floppy as A: (or B:).