MS-DOS 6.22 Boot Configuration Blocks File

In MS-DOS 6.22, the file responsible for defining user configuration block settings during the boot process is CONFIG.SYS. Located in the root directory of the startup drive (typically C:\CONFIG.SYS), this primary text file configures system hardware, allocates memory managers, and structures startup menus. This guide explains how CONFIG.SYS uses configuration blocks to let users choose different hardware and memory setups at boot time, along with how it integrates with AUTOEXEC.BAT.

The Role of CONFIG.SYS in the Boot Process

During startup, after the system loads the core MS-DOS files (IO.SYS and MSDOS.SYS), MS-DOS automatically searches for and parses CONFIG.SYS. In version 6.22, this file can contain multi-configuration blocks that give users an interactive menu to choose distinct startup environments, such as configurations tailored for conventional memory optimization, CD-ROM support, or expanded memory (EMS).

Anatomy of Configuration Blocks

MS-DOS 6.22 organizes multi-configuration menus using specific block headers enclosed in square brackets:

  • [menu]: Defines the menu structure. It contains commands such as menuitem, menudefault, and menucolor.
  • menuitem=BlockName, Menu Text: Associates a user-selectable label with a specific configuration block.
  • [BlockName]: Contains the specific drivers and settings (such as DEVICE, DEVICEHIGH, DOS=HIGH,UMB, and BUFFERS) executed only when that block is selected.
  • [common]: Contains commands executed across all configurations, regardless of the user's choice. It is standard practice to place a [common] block at the end of the file so third-party software installers append directives globally.

Example CONFIG.SYS Implementation

Below is a standard multi-configuration setup in CONFIG.SYS:

[menu]
menuitem=CDROM, Boot with CD-ROM Support
menuitem=NOCD, Boot without CD-ROM Support
menudefault=CDROM,10

[common]
DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\DOS\EMM386.EXE NOEMS
DOS=HIGH,UMB

[CDROM]
DEVICEHIGH=C:\DOS\OAKCDROM.SYS /D:MSCD001

[NOCD]

[common]
FILES=40
BUFFERS=30

Integration with AUTOEXEC.BAT

When the user selects an option from the menu, MS-DOS 6.22 assigns the chosen block name to an environment variable named %CONFIG%. The system then processes AUTOEXEC.BAT, where conditional branching logic (using GOTO %CONFIG%) executes matching startup programs and drivers, such as MSCDEX.EXE for CD-ROM drives or specific mouse drivers.