3.3 OPERATING SYSTEMS OPERATING SYSTEMS FOR COMPUTERS AND MOBILE DEVICES 1 An (O/S) is a system of different programs that work together to control and manage the hardware to provide the most efficient use of the available equipment and memory resources, and to act as an interface between the computer and the user. operating system 2 The main parts of an O/S The most important part of the O/S consists of the , which control all the other programs in the O/S, and the , which provide system services to the user. These fall into two categories: utility programs and system aids. supervisory programs service programs allow files to be saved, copied, renamed, or deleted. They activate all peripheral devices and are able to format a disk in preparation for storing information. Utility programs assist the user when developing a program. Any system errors experienced in a program at runtime will be located and identified by the O/S. System aids also include translation programs such as assemblers, interpreters, and compilers. System aids Types of operating systems The most common types of O/S are: : one application program is run at a time, both in real-time and batch processing. In , the user interacts with the computer during the execution of a program, meaning that the computer can respond immediately to inputs; in , a series of programs are run in sequence, and output is only provided at the end. Single program real-time processing batch processing : a number of users use the computer system simultaneously. The computer resources are time-shared among the users, each user having exclusive use of the resources at any one time. As all operators are offered a time in turn, every user feels as though they have exclusive use of a computer all the time. Multi-user slice : a complex program is run on more than one CPU at the same time. The CPUs are linked in parallel, as in the case of supercomputers. Multi-processing : more than one program can run simultaneously. Different areas of primary storage are reserved for each program, and any one particular program can be called into operation by the user at any time. Multi-programming or multi-tasking : different parts of a single program run simultaneously. Multi- threading : data is moved between primary and secondary storage as and when the primary storage too small. The user experiences the impression of a computer with larger memory. Virtual storage proves : different users can use different operating systems simultaneously on the same PC. Virtual machine : various computer systems connected to each other using a shared communication network have their own CPU, main memory, secondary memory, and resources. Distributed MORE Besides computers and mobile devices, other devices which perform a specific task, like a washing machine or a microwave oven, have an embedded operating system. This O/S allows the software which runs the programs to access device hardware. 1 MORE The first operating system as we know it today was developed by IBM in the 1960s for the System/360 series of machines, all with the same instructions and input/output architecture. 2