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SYSTEM SECURITY

OBJECT:TO DESIGN AND DEVELOPED A PASSWORD ROUTINE WHICH ACTIVATE AT THE START OF THE BOOTING OF A COMPUTER.

Design Interface Layout of the utility.
Writing on boot sector.
Successfully Interface Implemented.
Writing On boot sector not implemented.
Only studied boot record, deletion and writing on sector.

Save password in a file.

BRAIN DEBUGGERS

Department of Computer Science

University of Karachi-Pakistan

Brain.debuggers@usa.net

Dos Boot Process

When a PC is turned on, the CPU begins executing instructions from a location fixed when the chip was designed. i.e during the Power up sequence, the 8086/8088 microprocessor, by virtue of its design, automatically executes the instruction located at physical address FFFF0h, as in the table mention below:

STATE OF THE 8068/8088 ON POWER ON OR RESET

COMPONENTS STATUS

Flags All cleared

IP register 0000h

CS register FFFFh

DS register 0000h

SS register 0000h

ES register 0000h

At FFFF0h, IBM BIOS contain a jump instructon to a routine that performs several hardware tests. When these test conclude the SOFT RESET routine checks for a diskette in drive number 0 and, if present, read the diskettes side 0, track 0, and sector no 1 (called the Boot Sector) into memory at logical address 0000:7c00h.

Finally Boot transfers execution to the instruction location at the address, upto this part the programmer cannot interfere with the power-up sequence, that of replacing the BIOS.

ROM BOOTSTRAP LOADER:

The Rom Bootstrap loader is the heart of the boot sequence. After peripherals identified in Rom Bios have been identification tested and initialization the Boot Sector and system files are loaded into memory at physical address 0000:7c00h

By this ROM Bootstrap Loader. These programmes are too large or too variable (depending upon the System Configuration) or too infrequently used to be included in ROM. Since the operating System is not yet available, the loader of the boot programme must be done at a very basic level only what is known about the disk in ROM BIOS can be used.

 Boot Programme:

 The boot sector contains information about the system and disk organization (BPB) as well as that programmme (the boot program or disk bootstrap loader). The boot program uses BIOS service available in ROM and information from the BPB to load the IO.SYS file, which contains the additional BIOS routine and the sys files modules that controls the rest of the system restart.

 IO.SYS

It contains various BIOS routine not supplied with ROM, usually unique to a particular manufacturer or system configuration. IO.SYS contains sysinit, which relocates MSDOS.SYS the DOS Kernel to its final location. Bootstrap loader loads IO.SYS, which in turns loads MSDOS.SYS.

MSDOS.SYS

It comprises the Dos kernel routine providing the essential Dos service that remains memory resident.

CUSTOMIZING BOOT STRAP LOADER

Naturally the boot record on the diskeete corresponding to the MSDOS operating system, which takes over execution at this time. For many applications that runs under MSDOS this sequence of events in quite convinience. The programme manual for the application usually includes instructions for incorporating DOS into the program or vice versa. Boot circumstances arise. That requires by passing this conventional sequence of operation in situations like the following:

  1. In creating system program that receive control directly from BIOS, as would be a new DOS .
  2. In executing programs do not requires the services provided by MS DOS or that can profit from not considering with MS DOS in one or more of the following ways.
  1. Greater diskette stroage space
  2. Greater RAM avaibility
  3. Greater software independence

The BIOS strap differs from conventional assembly language code in the following points:

  1. The routine is automatically loaded from disk 0, track 0, and sector number 1 to the absolute address 0000:7c00h
  2. The routine cannot exceed one standard disk sector that is 512.
  3. CS: IP cannot be specified in the service.
  4. Segment fix ups cannot be present. The routine must executes at the absolute address 7c00h and cannot be loaded or relocated by the DOS command processor.
  5. The bootstrap programme can use BIOS services, since BIOS has been initialized at this time but not the service provided by the DOS.