新编计算机专业英语3、选择填空

三、选择填空

Operating system for micro, mini, and mainframe computers perform many services. These services can be classified either as“external”or“internal”.

The operating system provides external services that help users start programs, manage stored data, and maintain security. You, as the computer user, control these external functions. Using a command-line, menu-driven, or GUI user interface , an operating system provides you with a way to select the programs you would like to use. The operating system also helps you find, rename, and delete documents and other data stored on disks or tapes. On many, but not all computer systems , the operating system helps you maintain security by checking your user ID(用户标识) and password , as well as protecting your data from unauthorized access and revisions(修改).

The operating system provides internal services“behind the scenes”to ensure that the computer system functions efficiently . These internal services are not generally under your control , but instead are controlled by the operating system itself. The operating system controls input and output, allocates(分配) system resources, manages the storage space for programs and data, and detects equipment failure without any direction from you.

A programming language provides the tools a programmer uses to create software and produce a lengthy list of instructions, called source code ,which defines the software environment in every detail-what it looks like ,how the user enters commands ,and how it manipulates data. A computer’s microprocessor understands only machine language. Therefore, instructions written in a(n)high-level language must be translated into machine language before a computer can use them.

The process of translating instructions from a high-level language into machine language can be accomplished by two special types of programs: compilers and interpreters . A compiler translates all the instructions in a program as a single batch(一批) ,and the resulting machine language instructions, called object code(目标代码),are placed in a new file . Most of the program files on a distribution CD for commercial software are compiled so that they contain machine language instructions that are ready for the processor to execute.

As an alternative to a compiler, an interpreter converts one instruction at a time while the program is running . An interpreter reads the first instruction, converts it into machine language, and then sends it to the microprocessor. After the instruction is executed , the interpreter converts the next instruction, and so on.