The Boot Process in DOS

Execute ROM diagnostic Program

Errors Detected?
yes, Display Error Messages
No, then

Load DOS Hidden
System Files(IO.SYS, MSDOS.SYS)

CONFIG.SYS Files?
yes, Re-configure DOS in RAM
No, then

Load COMMAND.COM File
(Internal DOS Commands)

AUTOEXEC.BAT file?
yes, Execute Commands in AUTOEXEC.BAT file
No, then

Prompts for System DATE and TIME

Display the Default System Prompt


CONFIG.SYS File

DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\DOS\EMM386.EXE NOEMS HIGHSCAN
DOS=HIGH,UMB
DEVICEHIGH=C:\DOS\MOUSE.SYS
DEVICEHIGH=C:\DOS\RAMDRIVE.SYS 1024 /E
SHELL=C:\DOS\COMMAND.COM C:\DOS\ /E:2048 /P
BUFFERS=30
FILES=40

  • EMM386,EXE manages the upper memory area on 386 and 486 PCs. It makes sure that no two programs (or device drivers) use the same memory area at once. Like HIMEM.SYS, EMM386.EXE is loaded with the DEVICE command. A new HIGHSCAN option directs DOS to aggressively search the upper memory area for available space. This option can yield up to 64KB of additional memory. HIGHSCAN finds and uses the small upper memory blocks that remained unused in the past.

  • Expanded memory is addtional memory installed on an expanded memory board. Because programs can only use expanded memory 64KB at a time, it is slower than extended memory. EMM386 can simulate expanded memory for programs that require it. If any application programs are designed to use expanded memory (EMS), change the NOEMS parameter of EMM386.EXE to RAM.

  • The DOS=HIGH command loads device drivers in the upper memory area.

  • SHELL represents the name of the command interpreter to load. The default command interpreter is the COMMAND.COM file. ALthough the SHELL command can be used to specify a different command interpreter, SHELL is most often used to increase the size of your environment space.

  • BUFFERS is the number of input/output buffers(RAM) needed to improve disk performance. By specifying a higher number of buffers, you tell DOS to read a larger chunk of data from your disk into RAM every time. Data stored in RAM is instantly available. A recomnended setting of 20 buffers will suit most circumstances. Each buffer uses 512 bytes of memory.

  • FILES is the number of files that can be used at once by your programs. That DOS default is only eight. It is recommended that you have at least 40 files specified, as the number of open files include the hidden system files, COMMAND.COM, and Terminate-and-Stay-Resident (TSR) programs. Database and Windows applications often require 30 to 40 files open at a time.

  • DEVICE is a particular device driver, such as ANSI.SYS, MOUSE.SYS. Some device drivers short programs that tell DOS how to handle input/output from a given device, such as a keyboard, disk, or mouse. A configuration command must be supplied for each device you wish to install.


    AUTOEXEC.BAT File

    PATH C:\DOS;C:\UTIL;C:\MENU
    PROMPT $P$G
    SET DIRCMD=/ON
    SET TEMP=C:\DOS
    DEL C:\DOS\*.TMP
    COPY C:\SSFILES\BUDGET.WK1 A:BUDGET.BAK
    CD C:\SS
    LOTUS

  • Sets default search path to use C:\DOS, C:\UTIL, and C:\MENU.
  • Causes the system prompt to display the current disk and directory.
  • Sets the default for directory listings to be in filename sequence.
  • Sets C:\DOS as the default directory for any temporary files created by DOS or application program.
  • Deletes any temporary files on the DOS directory.
  • Copies a file in the SSFILES directory of the hard disk to Drive A.
  • Changes to the SS directory on the hard disk.
  • Executes an application program called LOTUS.

    To load a CD-ROM Drive


    AUTOEXEC.BAT File "C:\MSCDEX /D:MSCD000 /L:E"
    CONFIG.SYS FILE "DEVICE=C:\CDROMDRV.SYS /D:MSCD000"

  • MSCDEX.EXE is a DOS external command. "/D:" is driver and "/L:" is drive letter
  • CDROMDRV.SYS is an example of CDRom Device Driver that came with the CD-ROM drive's manufacturer