历年大学生英语竞赛试题(13)

fact,necessarily similar in design to a hard drive,although there are significant differences in speed of data access.

Most modern hard drives incorporate several

platters(磁盘) to further reduce the time spent seeking

the required information. Also,some newer drives have

two heads;one for reading,and a second head for writing

data to disk.This separation of tasks enables much

higher densities of magnetic information to be written

on the platter,which increases the capacity of the hard

drive.

There are three important ways in which the capacity of hard disks has been increased.First,the data code itself has been tightened with express coding

techniques.Second,as previously noted,the head

technology has been improved;and third,the distance

between the heads and the platters has been greatly

reduced.It is hard to believe,but the head can be made

to pass over the magnetised platter at distances of less than 1 microinch(the width of a typical human hair is 5000 microinches).This is achieved by means of a special protective coating applied to the platter.Each of these three improvements enables speedier access to the data.

Hard drives are more commonplace than tape recorders these days,but it must be remembered that they are much more fragile.Treated with respect they may last a number of years,but they are quite easily damaged,often with disastrous consequences for the user,whose precious data can become lost forever.Dropping a drive is almost always fatal,as is passing an incorrect electrical current through one(by faulty connection).Dust and even extremes of temperature can cause failure. Yet,no physical damage can ever result from the input of data via the keyboard or mouse.Of course,over time the magnetised coating on the platters will erode,yet this is almost entirely independent of the amount of use.

There are serious questions being raised about the

direction of the future of electronic storage media.Some researchers claim that it would be wiser to invest more time and money in setting up systems for streaming data across networks of computers from centralised banks of information storage.This would avoid the need for each personal computer user to have his or her own copy of a software program resident on a local hard drive.Personal data files could be kept at a central storage unit,and be suitably protected from disaster by a fail?safe(具有自动防止故障特性的) backup system.