Software and Operating Systems: Types, Functions and MCQs

A computer is two things at once. The machine you can touch is hardware; the set of instructions that tells the machine what to do is software. Every question an examiner asks in the Computer Awareness section about Windows, Linux, Android, booting or memory management sits inside this one division, so it is worth fixing the vocabulary before anything else. Software is intangible, it is written in a programming language, and it can be copied, updated or deleted without opening the cabinet.

The two families of software

Software is classified into system software and application software. System software runs the machine itself: the operating system, device drivers, language translators and utility programs. Application software does a user job: a word processor, a spreadsheet, a browser, a billing package. A third term, firmware, sits between the two; it is software written permanently into a chip, such as the BIOS on the motherboard, and the machine cannot start without it.

Language translators belong to system software and are asked often. An assembler converts assembly language into machine code. A compiler translates a whole high level program into machine code in one pass and reports all errors together. An interpreter translates and executes the program line by line, so it stops at the first error. A linker joins object modules, and a loader places the program in main memory for execution.

What an operating system does

The operating system is the system software that acts as the interface between the user and the hardware. It is loaded first and it stays in memory as long as the machine is on. Its standard functions are process management, memory management, file management, device management, security and job scheduling. It also provides the user interface, which may be a command line interface, where the user types commands, or a graphical user interface, which uses windows, icons, menus and a pointer.

Types of operating system

A batch operating system groups similar jobs and runs them without user interaction. A multiprogramming system keeps several programs in memory so the processor never sits idle. A time sharing or multitasking system gives each user a small slice of processor time in turn, so many users feel served at once. A real time operating system guarantees a response within a fixed time and is used in missile control, medical equipment and industrial plants. A distributed operating system shares work across several connected computers. A network operating system manages servers, printers and shared files on a network.

Kernel, booting and scheduling

The kernel is the core of the operating system, the part always resident in main memory, and it controls the processor, memory and devices. A monolithic kernel keeps all services in one block; a microkernel keeps only the essentials in the kernel and moves the rest out. The shell is the outer layer that takes the user command and passes it to the kernel.

Booting is the process of starting the computer and loading the operating system into main memory. A cold boot is starting a machine that was switched off; a warm boot is restarting a machine already on. On start-up the BIOS runs the power on self test, which checks the hardware, and the bootstrap loader then brings the operating system in from disk.

Scheduling decides which ready process gets the processor next. First Come First Served serves processes in arrival order. Shortest Job First picks the process with the smallest burst time. Round Robin gives every process a fixed time quantum in rotation and is the method used by time sharing systems. When two processes each hold a resource the other needs and neither will release it, the system is in deadlock.

Memory, files and famous names

Virtual memory lets the operating system use a part of the hard disk as though it were main memory, so a program larger than the installed RAM can run; the technique of moving fixed size blocks between disk and memory is paging, and excessive paging that leaves no time for real work is called thrashing. Spooling places output in a queue on disk so that slow devices such as printers do not hold up the processor.

A file system decides how data is stored and named on a disk. FAT32 and NTFS belong to Windows, ext4 to Linux. Among the operating systems themselves, UNIX was developed at Bell Laboratories in 1969 by Ken Thompson and Dennis Ritchie, Linux was released in 1991 by Linus Torvalds and is free and open source, MS-DOS was a single user command line system, Windows brought the graphical interface to the personal computer, and Android is built on the Linux kernel.