tailieunhanh - Operating-System concept 7th edition phần 2

Phân bổ nguồn lực. Khi có nhiều người dùng hoặc nhiều công việc đang chạy tại cùng một thời gian, nguồn lực phải được phân bổ cho mỗi {hem. Nhiều loại khác nhau của tài nguyên được quản lý bởi hệ điều hành. Một số (chẳng hạn như chu kỳ CPU, bộ nhớ chính, và lưu trữ tập tin) | User Operating-System Interface 41 Resource allocation. When there are multiple users or multiple jobs running at the same time resources must be allocated to each of Ềhem. Many different types of resources are managed by the operating system. Some such as CPU cycles main memory and file storage may have special allocation code whereas others such as devices may have much more general request and release code. For instance in determining how best to use the CPU operating systems have CPU-scheduling routines that take into account the speed of the CPU the jobs thatmustbe executed the number of registers available and other factors. There may also be routines to allocate printers modems USB storage drives and other peripheral devices. Accounting. We want to keep track of which users use how much and what kinds of computer resources. This record keeping may be used for accounting so that users can be billed or simply for accumulating usage statistics. Usage statistics may be a valuable tool for researchers who wish to reconfigure the system to improve computing services. Protection and security. The owners of information stored in a multiuser or networked computer system may want to control use of that information. When several separate processes execute concurrently it should not be possible for one process to interfere with the others or with the operating system itself. Protection involves ensuring that all access to system resources is controlled. Security of the system from outsiders is also important. Such security starts with requiring each user to authenticate himself or herself to the system usually by means of a password to gain access to system resources. It extends to defending external I O devices including modems and network adapters from invalid access attempts and to recording all such connections for detection ofbreak-ins. If a system is to be protected and secure precautions must be instituted throughout it. A chain is only as strong as its .

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