Personal-Computer Systems

Personal-Computer Systems

As hardware costs have decreased, it has once again become feasible to have a computer system dedicated to a single user. These types of computer sys­tems are usually referred to as personal computers (PCs). The I/O devices have certainly changed, with panels of switches and card readers replaced with type writer like keyboards and mice. Line printers and card punches have suc­cumbed to display screens and to small, fast printers.

Personal computers appeared in the 1970s. They are microcomputers that are considerably smaller and less expensive than mainframe systems. During their first decade, the CPUs in PCs lacked the features needed to protect an oper­ating system from user programs. PC operating systems therefore were neither multiuser nor multitasking. However, the goals of these operating systems have changed with time; instead of maximizing CPU and peripheral utilization, the systems opt for maximizing user convenience and responsiveness. These systems include PCs running Microsoft Windows, and the Apple Macintosh. The MS-DOS operating system from Microsoft has been superseded by multi­ple flavors of Microsoft Windows, and IBM has upgraded MS-DOS to the OS/2 multitasking system. The Apple Macintosh operating system has been ported to more advanced hardware, and now includes new features such as virtual memory.

Operating systems for these computers have benefited from the develop­ment of operating systems for mainframes in several ways. Microcomputers were immediately able to adopt the technology developed for larger operating systems. On the other hand, the hardware costs for microcomputers are sufficiently low that individuals have sole use of the computer, and CPU utilization is no longer a prime concern. Thus, some of the design decisions that are made in operating systems for mainframes may not be appropriate for smaller systems. For example, file protection may not seem necessary on a personal machine.