The DOS boot sequence

The DOS boot sequence

Yes, you will see references to the DOS boot sequence on the exams. Virtually every PC goes through about the same sequence of events when starting up, regardless of the operating system it uses.

Memorize the DOS boot sequence and remember the sequence of the files.

Remember After the POST completes, the MS-DOS system loads using the following steps:

1. The CMOS indicates the sequence in which the disk drives (A, C, and so on) are scanned for a boot record.

2. If the boot device is the C drive, the Master Boot Record (MBR) loads, and its program locates the boot partition.

3. If the boot disk is the A drive, or if the C drive boot is continuing, the DOS Boot Record (DBR) loads, and control passes to it.

4. The DBR loads the IO.SYS and MSDOS.SYS files (which is most of DOS) and passes control to them.

5. IO.SYS loads CONFIG.SYS (required by DOS systems), which sets the environment and loads the device drivers.

6. The COMMAND.COM command interpreter then loads, and control passes to it.

COMMAND.COM loads and executes the AUTOEXEC.BAT and then displays the user interface (the command prompt).

Instant Answer The DOS boot sequence is IO.SYS, MSDOS.SYS, CONFIG.SYS, COMMAND.COM, and AUTOEXEC.BAT.

Following the DOS PATH

The DOS PATH= statement that is placed in the AUTOEXEC.BAT file is mentioned at least once on the exam. The context goes something like this: Why would a certain file when entered on the command line prompt result in the message, "Bad or missing file name?"

The PATH statement establishes the directory sequence and priority for where the operating system is to look for command-line files. For example, this statement in the AUTOEXEC.BAT file means that the system should look in the DOS directory first and then the Windows directory for a command entered on the command line.

PATH=C:\DOS;C:\WINDOWS