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1. 1 What are the three main purposes of an operat ing system?
1To provide an en vir onment for a computer user to execute programs on computer
hardware in a convenient and ef?cie nt manner.
2To allocate the separate resources of the computer as n eeded to solve the problem
give n. The allocati on process should be as fair and ef?cie nt as possible.
3As a control program it serves two major functions: (1) supervision of the execution of user programs to preve nt errors and improper use of the computer, and (2) man age- ment of the operati on and con trol of I/O devices.
环境提供者，为计算机用户提供一个环境，使得能够在计算机硬件上方便、高效的执行程序 资源分配者，为解决问題按需分配计算机的资源，资源分配需尽可能公平、高效 控制程序
监控用户程序的执行，防止出错和对计算机的不正当使用 管理丨/〇设备的运行和控制
1.2List the four steps that are n ecessary to run a program on a completely dedicatedmachi ne.
An swer: Gen erally, operati ng systems for batch systems have simpler requireme nts tha n for pers onal computers. Batch systems do not have to be con cer ned with in teract ingwith a user
as much as a personal computer. As a result, an operatingsystem for a PC must be concerned
with resp onse time for an in teractive user. Batch systems do not have suchrequireme nts.
A pure batch system also may have not to handle time sharing,whereas an operating systemmust switch rapidly betwee n differe nt jobs.
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1.6 Define the esse ntial properties of the follow ing types of operat ing systems:
a.Batch
b.In teractive
c.Time shar ing
d.Real time
ework
f.Distributed
a.Batch. Jobs with similar n eeds are batched together and run through the computer as a group by an operator or automatic job seque ncer. Performa nee is in creased by attempting to keep CPU and I/O devices busy at all times through buffering, off-line operati on, spooli ng, and multiprogram ming. Batch is good for executi ng large jobs that need little interaction; it can be submitted and picked up later.
b.In teractive. This system is composed of many short tran sacti ons where the results of the n ext tran sacti onmay be un predictable. Resp onse time n eeds to be short (sec on ds) since the user submits and waits for the result.
c.Time shar in g.Thissystemsuses CPU scheduli ng and multiprogram ming to provide econo mical in teractive use of a system. The CPU switches rapidly from one user to
ano ther. In stead of hav ing a job de? ned by spooled card images, each program readsits next control card from the terminal, and output is normally printed immediately to the scree n.
d.Real time. Often used in a dedicated application, this system reads information from
sen sors and must resp ond with in a?xed amou nt of time to en sure correct perfor-
man ce.
ework.
f.Distributed.This system distributes computati on among several physical processors.