developed in the 1970s to support the UNIX operating system. is a highly portable general-purpose language.
Other such languages are APL (developed in 1962), PASCAL (named after Blaise Pascal and developed in 1971), and LISP and PROLOG, both of which are used for work in artificial intelligence. LOGO is a development of LISP which has been used to develop computer-based training (CBT) packages.
When a program written in one of these high-level languages is designed to do a specific type of work such as calculate a company's payroll or calculate the stress factor on a roof, it is called an applications program. Institutions either purchase these programs as packages or commission their own programmers to write them to meet the specifications of the users.
The program produced after the source program has been converted into machine code is referred to as an object program or object module. This is done by a computer program called the compiler, which is unique for each computer. Consequently, a computer needs its own compiler for the
various high-level languages if it is expected to accept programs written in those languages. For example, in order that an IBM RS/6000 may process a program in FORTRAN, it needs to have a compiler that would understand that particular model and the FORTRAN language as well.
The compiler is a systems program which may be written in any language, but the computer's operating system is a true systems program which controls the central processing unit (CPU), the input, the output, and the secondary memory devices. Another systems program is the linkage editor, which fetches required systems routines and links them to the object module (the source program in machine code). The resulting program is then called the load module, which is the program directly executable by the computer. Although systems programs are part of the software, they are usually provided by the manufacturer of the machine.
Unlike systems programs, software packages are sold by various vendors and not necessarily by the computer manufacturer. They are a set of programs designed to perform certain applications which conform to the particular specifications of the user. Payroll is an example of such a package which allows the user to input data - hours worked, pay rates, special deductions, names of employees - and get salary calculations as output. These packages are coded in machine language (Os and Is) on magnetic tapes or disks which can be purchased, leased, or rented by users who choose the package that most closely corresponds t their needs.
Computer networks
Computer networks link computers by communication lines and software protocols, allowing data to be exchanged rapidly and reliably. Traditionally, networks have been split between wide area networks (WANs) and local area networks (LANs). A WAN is a network connected over long distance telephone lines, and a LAN is a localized network usually in one building or a group of buildings close together. The distinction, however, is becoming blurred. It is now possible to connect up LANs remotely over telephone links so that they look as though they are a single LAN. Originally, networks were used to provide terminal access to another computer and to transfer files between computers. Today, networks carry e-mail, provide access to public databases and bulletin boards, and are beginning to be used for distributed systems. Networks also allow users in one locality to share expensive resources, such as printers and disk-systems.
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Distributed computer systems are built using networked computers that co-operate to perform tasks. In this environment each part of the networked system does what it is best at. The high-quality bit-mapped graphics screen of a personal computer or workstation provides a good user interface. The mainframe, on the other hand, can handle large numbers of queries and return the results to the users. In a distributed environment, a user might use his PC to make a query against a central database. The PC passes the query, written in a special language (e.g. Structured Query Language-SQL), to the mainframe, which then parses the query, returning to the user only the data requested. The user might then use his PC to draw graphs based on the data. By passing back to the user's PC only the specific information requested, network traffic is reduced. If the whole file were transmitted, the PC would then have to perform the query itself, reducing the efficiency of both network and PC.
In the 1980s, at least 100,000 LANs were set up in laboratories and offices around the world. During the early part of this decade, synchronous orbit satellites lowered the price of long-distance telephone calls, enabling computer data and television signals to be distributed more cheaply around the world. Since then, fiber-optic cable has been installed on a large scale, enabling vast amounts of data to be transmitted at a very high speed using light signals.
The impact of fiber optics will be considerable to reduce the price of network access. Global communication and computer networks will become more and more a part of professional and personal lives as the price of microcomputers and network access drops. At the same time, distributed computer networks should improve our work environments and technical abilities.
Key
Unit I
I.
| A frequency range tool consequently fiber sample lesion hostile missile bore fraction simplify cauterize valuable vaporize tissue | B enormous extremely machine-tool unprecedented precise coherent induce | C amplification light beam exposure time |
II.
1) e; 2) g; 3) i; 4) b; 5) h; 6) j; 7) d; 8) c; 9) f; 10) a.
III.
| A | B | C | D |
| 1) b; | 1) c; | 1) d; | 1) d; |
| 2) a, b; | 2) c; | 2) a; | 2) a; |
| 3) c; | 3) d; | 3) c; | 3) b; |
| 4) a, b; | 4) a; | 4) b; | 4) b. |
IV.
,
()
,
,
10.
V.
scientif ic
power ful ,
effect ive , ,
success ful
select ive ,
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communica tive , ,
industri al
direction al
spaci ous ,
molecul ar
chemic al
VI.
emit radiate
produce manufacture
propagate spread
highly very
enormous huge
spot place
precise accurate
use apply
amount quantity
cause bring about
speed velocity
detect find out
reduction decrease
simplify facilitate
bore drill
propose suggest
VII.
a) 5; b) 13; c) 14; d) 1; e) 15; f) 12; g) 11; h) 10; i) 2; j) 7; k) 6; l) 3; m) 9; n) 8; o) 4.
Unit II
I. a) network, link, document, company, access, government, data, hierarchy, b) computer, resource, refer, display, c) information, multimedia, communication, worldwide, introduction.
II. 1d, 2b, 3f, 4e, 5a, 6c.
III. a) 1 b, 2 d, 3c, 4b; b) 1 c, 2 c, 3 a; c) 1 c, 2 d; d) 1 c.
IX. 1 c; 2 f; 3 b, e; 4 a, h; 5 g; 6 d.
Unit III
I. a) vast, frequency, pitch, altitude, threshold, strictly, permanent
b) collide, perceive, acoustic, involve, occur, particular
c) jet aircraft, engineer, sound-absorbing
Grammar Study
VII. 1. The members of the committee were expected to come to an agreement. , . 2. Many buildings were reported to have been damaged by the fire. , , . 3. The delegation is reported to have left London. , . 4. Many people are expected to attend the meeting. , . 5. She seems to know French well. , , . 6. He happened to be at home at that time. . 7. The house appears to have been built in the eighteenth century. , -, . 8. He seemed to know the subject well. , , . 9. They are not likely to return soon. , . 10. They are certain to be here on Monday. . 11. The meeting is unlikely to be postponed. . 12. His article is very likely to be published in the newspaper. , .
VIII. 1. payment to be made in cash in exchange for the bill of lading and insurance policy. 5.000 , . 2. the days at the port of loading not to commence before October 20. , 20- . 3. the goods to be shipped in two parcels. , 15- , . . , . 4. such payment to be made without prejudice to the buyers rights under the contract. , , , , .
CONTENTS
Unit I. Lazer...3-12
Grammar Study. Modal Verbs12-16
Unit II. Networks.16-25
Grammar Study. .......25-34
Sequence of Tenses.25-29
The Participles29-31
Absolute Participial Construction.31-32
Unit III. What is Sound?.............................................................................34-42
Grammar Study. .43-48
The Infinitive43-44
Complex Subject44-45
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Complex Object45
For with the Infinitive Construction.......45
Appendix. Supplementary Texts ...49-70
Key .71-73
