软件工程阅读之系统性能评价(中英文对照)

EVALUATING A SYSTEM’S PERFORMANCE
　　Operational software was designed to improve the efficiency of computer systems．DP professionals are constantly looking for signs that their computer hardware is not performing effectively．Processing delays，slow response times，frequent error states，and longer processing cycles are just a few of the signs of malfunctioning operational software．Examples of these types of inefficiencies are readily apparent in online processing systems．File inquiries that normally might take fractions of seconds now require seconds to complete．Processing time for programs in the job increases by 20 to 40 percent for no apparent reason[1]．There are complaints about increased response times in both peak and off-peak periods．These and other operational difficulties may signal that an operating system is under stress．
　　Though these examples may indicate inefficiencies in the operational software，they are insufficient for the systems programmer monitoring that performance．Programmers need more precise operational data upon which to base their analyses and evaluations．
　　Manufacturers accordingly modified their operational software to provide such statistics．This area of specialization，known as performance management，provides the data needed to evaluate a system’s level of performance．The performance management software is built into the operating system and can provide statistics relating to：
（1）The number and type of I / O operations and time required to perform them．
（2）The volume and frequency of access to files in the entire system．
（3）The average response time needed to handle online inquiries．
（4）The frequency of access to specific disk drives and the files maintained on that device．
（5）The volume of telecommunication traffic handled by specific channels．
（6）The usage times associated with all I / O devices．
（7）The amount of available CPU space during peak periods．
（8）The average time needed to process a tast in the job queue，broken down into waiting time and actual processing time．
（9）The frequency of use of the system’s utility software．
（10）The frequency of execution for all software run with the system．
　　These statistics can advise the systems programmer on the system’ s overall performance level．They are compared against earlier performance data and accepted norms（for that type of computer hardware）to determine whether the system is operating efficiently．This data helps system programmers decide if the existing perational software should be modified or whether a new operating system must be installed．
　　For example，performance management statistics may reveal that one disk drive is repeatedly used while others remain idle．This condition slows performance，as most of the drive’s actions relate to movement of the access arm，not file handling．It may also signal that two high-usage files are on the same disk and should be moved to separate drives[2]．The performance data may reveal that the telecommunications services supporting a user facility may be inadequate for their existing workload[3]．This often occurs as operational demands on an organization grow and shift in response to user and customer needs [4]．

NOTES
[1] 此句中“increasees by 20 to 40”意思是“增加了20% ~ 40%”。
[2] “should be moved to separate drives”是表示与现在相反的虚拟语句，“should be”常译为“本（应）该”。
[3] “that”到句末是由“that”引导的宾语从句；其中，“supporting a user facility”是现在分词短语，作定语修饰“the telecommunications services”。
[4] “shift”本意为“转移，改变”。