WHAT IS THE DOS BOOT SEQUENCE??

Short answer:
Power On Self Test (POST )which checks BIOS,CPU, RAM, Video, Keyboard,
drives, etc.
Load Operating System (OS)
? IO.SYS
? MSDOS.SYS
? CONFIG.SYS
? COMMAND.COM
? AUTOEXED.BAT
Specifics
1. BIOS locates the Master Boot Record (MBR) on the hard drive.
2. The partition table find the physical location of the logical boot drive and
turns to the boot record of that logical drive
3. The boot record (a very short program) loads two hidden files into
memory. These files are IO.SYS and MSDOS.SYS
o The IO.SYS file contains more BIOS software
o The MSDOS.SYS contains software to manage files, run
applications software and interface with hardware
4. Once these two files are loaded, the boot record program is longer needed
and turns control over to a file stored on MSDOS.SYS
5. This program looks on the hard drive for a file named CONFIG.SYS. This
is the first OS file that you, the user, can change. This file contains
commands that tell DOS how many files it can open at any one time
(FILE=) and how many file buffers (a temporary holding area for a file) to
create (BUFFERS=). It also contains the commands to load device drivers
(small programs that tell your computer how to communicate with devices
such as printers) (DRIVERS=) and other information. Several drivers can
be loaded into memory and CONFIG.SYS puts them anywhere it wants
unless the program requests a certain memory location.
6. When CONFIG.SYS is done, MSDOS looks for another file called
COMMAND.COM. This file consists of 3 parts: more code to manage
Input/Output (I/O), internal DOS commands such as COPY and DIR, and
a short program that looks for AUTOEXEC.BAT.
7. AUTOEXEC.BAT stands for "automatically executed batch" program. This
file holds a list of DOS commands that are automatically executed each
time DOS loads. Two of these commands are:
o PROMPT $P$G this instructs DOS to display the current directory
name and the current drive name as part of the prompt.
C:\Windows instead of C:>.
o PATH Tells DOS where to look for program files. Example:
C:\Windows\Driver Cache \Fonts
o AUTOEXEC.BAT also loads TSRs (terminate and stay resident
programs).
8. The boot process is completed after AUTOEXEC.BAT has finished
executing. At this point, COMMAND.COM is in charge and you have the
command Prompt (C:>).