OPERATING SYSTEMS 9 OPERATING SYSTEMS (O/S) Answer these questions. a. What operating system does your mobile phone work on? b. And your computer? c. What O/S is the most popular among your classmates? bill: bolletta to be devised: essere concepito overall: complessivo to prove: risultare, rivelarsi room: spazio slice: fetta thread: filo The first operating system as we intend it today was developed by IBM in the 1960s for the System/360 series of machines, all with the same instruction and input/output architecture. An operating system 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. The most important part of the O/S consists of the supervisory programs, which control all the other programs in the O/S, and service programs, which provide system services to the user. These fall into two categories: utility programs and system aids. Utility 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. System aids assist the user when developing a program. Any system errors experienced in a program at run time will be located and identified by the O/S. However, logic errors must be located by the programmer. As the system must be capable of accepting information from the user in a programming language, systems aids also include translation programs such as assemblers, interpreters and compilers. Just as there are different types of computer systems, so there are different types of O/S. Here are the most common: single program: one application program is run at a time, both at real time and batch processing. In real time processing, the user interacts with the computer during the execution of the program and that means that the computer is able to respond immediately to inputs; in batch processing a series of programs are run in sequence as, for example, in the compilation of bills; multi-user: a number of users use the computer system at the same time. 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 slice in turn, every user has the impression that they have exclusive use of a computer all the time; multi-processing: a very 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-programming or multi-tasking: more programs appear to run at the same time. 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-threading: different parts of a single program run concurrently; virtual storage: data is moved between primary and secondary storage as and when the primary storage proves to be too small. The user has the impression of a computer with a larger memory; virtual machine: different users can use different operating systems simultaneously on the same PC. 126 Module 3 FLOWCHARTING