Q12. What are the different files present in DOS? Explain its drawbacks.
Answer:
Files Present in DOS
Files may include program or any other information. It is necessary to assign a name these files so that it becomes easier to identify them. Dos allows the user to assign file names which basically consist of two parts,
1. Primary names
2. Secondary names.
1. Primary Names
The primary names comprises of eight characters including alphabets, numbers, characters, hypen.
2. Secondary Names
The secondary names are maximum of three character long. These names are optional.
Both primary name and secondary names are separated by a dot.
The following are the two important files of DOS,
(a) CONFIG.SYS
(b) AUTOEXEC.BAT
(a) CONFIG.SYS
This file consist of those commands required for setting up different parameters. It is a special file comprising of setup and configuration instructions belonging to the computer system. It is considered as the primary configuration for DOS and OS/2 operating system. CONFIG.SYS file is located in the root directory from which DOS can be booted. This files is loaded each time the computer first boots up. It is responsible for controlling the components connected to the computer such as memory and other hardware devices.
(b) AUTOEXEC.BAT
This file was used in MS-DOS and in early versions of Microsoft Windows operating system. It manages and executes other programs that are listed in the file is a special DOS batch file stored in root directory. Upon starting or restarting the computer is automatically executed and is used to load TSR (Terminate and Stray Resident) programs that are present in the memory and pop-up whenever user invokes them. The main purpose of AUTOEXEC.BAT file is to set environment variables such as keyboard, printer and temporary file location. It is also used to start low-level system utilities like Virus scanners, Mouse drivers, Keyboard drivers, CD drivers etc.
Drawbacks of DOS
DOS has an upper limit to the size of hard disk partitions. This is because of the following two reasons:
1. DOS operating system never provided any support for file system that were newer than FAT 16.
2. The hard disk is accessed by DOS by invoking interrupt 13. This interrupt call uses the cylinder-head sector system which is relative to the disk mapping. The drawback of this system is that only 8 gigabytes of memory is visible to the operating system. Most of the present days operating system carried out disk access by mean of different software.
Despite of these drawbacks DOS is still used in many embedded systems due to the following reasons.
(i) Simple architecture
(ii) Minimal memory and processor
requirements.
