Disk Operating System (DOS)

Description and characteristics of DOS Sessions in MS-Windows 95, 98, and XP. How to start and customize the DOS Session.

MS-DOS Sessions in Windows

Starting DOS Sessions in MS-Windows

Starting an MS-DOS session from within the MS-Windows 95,98,XP GUI causes VMM (virtual machine manager) to create virtual machine for the session with 1mb of memory (640kb conventional and 384kb of upper memory). VMM also creates a DOS environment based on defaults in IO.SYS and any other settings in AUTOEXEC.BAT and CONFIG.SYS.

DOS sessions have access to long file names, multitasking, 32-bit disk caching, protected mode drivers for the mouse and CD-ROM, etc. etc.

Starting DOS Sessions (type EXIT to return to GUI)

Method Notes
Run Command Can use parameters and switches for COMMAND.COM (see Unleashed; p.660) Starts DOS in drive/directory currently selected in Windows Explorer (or C:\WINDOWS\DESKTOP if Explorer not open)
Start Menu, Programs, MS-DOS Prompt This shortcut is not always present
Double-click COMMAND.COM Double-click on C:\COMMAND.COM or C:\CMD\COMMAND.COM from Windows Explorer
Create shortcut to DOS on desktop or Start menu Can use parameters and switches for COMMAND.COM (see Unleashed; p.660)
Open folder in DOS Window from Windows Explorer context sensitive menu First create a new action for Explorer's context-sensitive menu

Customizing DOS Session Settings

There are many settings for DOS Sessions. These settings are made using the properties sheet either for a program or a shortcut.

When you set the properties for either a DOS program or a shortcut to a DOS program you are actually creating a PIF for that program.

Unless you want to start the program by double-clicking on its icon in Windows Explorer there is little point in setting the properties for the program file itself.

It is much more convenient to start programs either directly from the Start menu or the desktop or from a folder in the Start menu or the desktop. To do so we do not place programs themselves on the desktop or the Start menu, we put a Shortcut to the program in one of those places. Therefore it is more common to set up the properties for a program's shortcut then for the program itself.

The properties sheet for a shortcut is accessed by right-clicking on the shortcut and then choosing Properties. The properties sheet has five tabs, each with its own settings:

Program Tab

Setting Explanation
Command Line Path and name for the program, as well as any parameters or switches.
Working What the current drive and path should be when the program is started. DOS programs sometimes need to find their data in the current directory, or this may just be for the user's convenience when retrieving files.
Batch file Specify a batch file to run before the program is started. A batch file may be used to set environmental variables, copy files, change the path, load tsr, etc.
Shortcut key Ctrl-Alt-key keyboard shortcut to launch the program.
Run Normal, Minimized, or Maximized window (also see Screen)
Advanced This is where you can specify MS-DOS Mode for a program. When MS-DOS Mode is specified none of the other settings are used because Windows will boot to Real Mode. See Customizing MS-DOS Mode below.
Change icon Specify a path and filename for the icon to represent the shortcut.
Close on Exit Check this box to have windows close the window when the DOS program terminates.

Font Tab

Setting Explanation
Font size Choose a font size for the program to use when it runs in a window.

Memory Tab

Setting Explanation
Conventional Memory
  • Total. VMM gives every DOS session 640k of memory by default. Many don't need that much, so specify less to conserve system resources (or reduce paging to the swap file, as is the case).
  • Initial environment. Increase the size of the DOS environment for the DOS session.
  • Protected. Check off to write protect system memory area and prevent the DOS app from crashing Windows.
Expanded (EMS) memory Total. Set to none if you know the program doesn't use expanded memory, or limit it to a specific amount rather than let VMM give the app as much as it likes. Note: if not available it probably means that NOEMs is in the CONFIG.SYS.
Extended (XMS) memory
  • Total. Ditto Expanded memory.
  • Uses HMA. Should program have access to HMA? Probably not, but perhaps to load device driver.
MS-DOS protected mode (DPMI) memory Amount of protected mode memory available to the app.

Screen Tab

Setting Explanation
  • Run program full-screen or in a window.
  • Number of lines on screen (both full-screen and window).
  • Display toolbar by default.
  • Restore settings on startup. Restores the window size and position from the last session if checked.
  • Fast ROM Emulation. When checked allows Windows to emulate ROM BIOS video services with RAM-based virtual VxD's (virtual device drivers), which are faster. Disable is compatibility issues due to program making non-standard ROM calls.
  • Dynamic memory allocation. When checked allows VMM to reduce (and therefore conserve) allocated memory when a DOS program switches from Graphics mode to text mode. Unchecking it forces VMM to always give enough for graphics mode.

Misc Tab

Setting Explanation
Allow screen saver when program is in foreground? No for communications programs or if screen saver causes a conflict with program. (DOS box becomes minimized when screen saver kicks in)
  • QuickEdit. Enables selection of text with mouse when program running in a window.
  • Exclusive Mode. Use only if mouse won't otherwise work in DOS program.
Background Always suspend in background? Uncheck if program does no background processing to stop it from stealing cpu cycles from other running apps.
Termination Warn if still active. Warn you if you try to close the window without first shutting down the program (can cause loss of data).
Idle Sensitivity How much cpu time program gets when it is idle. The lower the Idle sensitivity the longer Windows waits before declaring the program idle and reducing its cpu cycles. This will increase efficiency of DOS programs which do process in background but, unlike Windows programs, have no way of communicating their current state.
Fast pasting How fast information is pasted from clipboard into the program. Many DOS programs can't handle full speed and text gets scrambled.
Windows Shortcut Keys Deactivates the windows shortcut keys if they are used by the program.

Bruce Miller, 2002, 2014