Гвоздева Цомпутер сциенце 2011

computer. The field is divided into two major branches: computability theory and complexity theory, but both branches deal with formal models of computation.

In order to perform a rigorous study of computation, computer scientists work with a mathematical abstraction of computers called a model of computation. There are several formulations in use, but the most commonly examined is the Turing machine. A Turing machine can be considered as a desktop PC with an infinite memory capacity, though it can only access this memory in small discrete chunks. Computer scientists study the Turing machine because it is simple to formulate, it can be analyzed and used to prove results, and because it represents what many consider the most powerful possible "reasonable" model of computation. While the infinite memory capacity might be considered an unphysical attribute, for any problem actually solved by a Turing machine the memory used will always be finite, so any problem that can be solved on a Turing machine could be solved on a desktop PC which has enough memory installed.

Computability theory

Computability theory deals primarily with the question of whether a problem is solvable at all on a computer. The halting problem is one of the most important results in computability theory, as it is an example of a concrete problem that is both easy to formulate and impossible to solve using a Turing machine. Much of computability theory builds on the halting problem result. Computability theory is closely related to the branch of mathematical logic.

Complexity theory

Complexity theory considers not only whether a problem can be solved at all on a computer, but also how efficiently the problem can be solved. Two major aspects are considered: time complexity and space complexity, which are respectively how many steps it takes to perform a computation, and how much memory is required to perform that computation.

* In order to analyze how much time and space a given algorithm requires computer scientists express the time or space required to solve

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the problem as a function of the size of the input problem. For example, finding a particular number in a long list of numbers becomes harder as the list of numbers grows larger. If we say there are n numbers in the list, then if the list is not sorted or indexed in any way we may have to look at every number in order to find the number we're seeking. We thus say that in order to solve this problem, the computer needs to perform a number of steps that grows linearly with the size of the problem.*

To simplify this problem, computer scientists have adopted Big O notation, which allows functions to be compared in a way that ensures that particular aspects of a machine's construction do not need to be considered, but rather only the asymptotic behavior as problems become large. So in our previous example we might say that the problem requires O(n) steps to be solved.

Vocabulary Notes

1.major – basic

2.rigorous – scrupulous

3.a chunk – a large amount or a part of something

4.a notation – a set of written symbols

5.to ensure – to guarantee

6.a previous example – the one that was described above

POST -READING TASK (to be done in writing)

I. Cut down each paragraph to the topical sentence(s) and write

asummary.

II. Formulate questions using the question words.

1.The theory of computation deals with whether and how efficiently problems can be solved on a computer. (What …………. with?)

2.This field is divided into two major branches. (Into what branches?)

3.Computer sciences work with a mathematical abstraction of computers called a model of computation. (What ………..with?)

4.The most commonly examined formulation is the Turing machine. (Which formulation …..?)

5.A Turing machine can be considered as a desktop PC with an infinite memory capacity. (How?)

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6.Computer scientists study the Turing machine …………... (Why?)

7.Computability theory deals primarily with the question of whether a problem is solvable at all on a computer. (What ……….. with?)

8.The halting problem is one of the most important results in computability theory. (Why?)

9.Complexity theory considers ………………... (What?)

10.Two major aspects are considered. (What aspects ……?)

11.Computer scientists express the time or space required to solve the problem as a function of the size of the input problem. (Why?)

12.Computer scientists have adopted Big O notation. (What …….

for?)

CLASS EXERCISES

Exercise 1 (in groups)

Using the questions formulated in post-reading task II discuss the theory of computation.

Exercise 2 (do it yourself)

Put the verbs into the passive.

1.This problem can (solve) on a computer.

2.This field (divide) into two major branches.

3.Several formulations (use).

4.A Turing machine can (consider) as a desktop PC with infinite memory capacity.

5.The infinite memory capacity might (consider) an unphysical attribute.

6.Any problem that can (solve) on a Turing machine could (solve) on a desk PC.

7.Computability theory closely (relate) with a branch of mathematical logic.

8.How efficiently can this problem (solve) on a computer?

9.Two major aspects (consider).

10.How much memory (require) to perform this computation?

11.The list (not sort).

12.The list (not index).

Exercise 3 (do it yourself)

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Translate the sentences.

1.Предметом теории вычислений является изучение возможности и эффективности решения задач на компьютере.

2.Существует несколько формулировок модели вычислений.

3.Учёные изучают Turing машину, потому что она является самой мощной из всех приемлемых моделей вычисления.

4.Эту задачу нельзя решить на компьютере.

5.Чтобы решить задачу компьютер должен выполнить целый ряд операций.

6.Количество операций возрастает линейно увеличению размера задачи.

7.Чтобы упростить эту проблему учёные приняли систему обозначений Big O.

UNIT 8

SUPERCOMPUTERS

PRE-READING TASK

Give Russian correspondence:

such as, and the like (and so on), conventional (usual, standard), through (due to), as well as (and too), to perform (to operate, to work), performance (characteristics), is due to (is caused by), to tend (to have a tendency), to make great efforts (to try hard), a bottleneck (a difficult problem), at least (as a minimum)

Terminology

latency − время ожидания

CALCULATION-INTENSIVE TASKS

Study the text and translate the passage marked with asterisks in writing.

Supercomputers are used for highly calculation-intensive tasks such as problems involving quantum mechanical physics, weather forecasting, climate research (including research into global warming), molecular modeling (computing the structures and properties of chemical compounds, biological macromolecules, polymers, and crystals), physical

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simulations (such as simulation of airplanes in wind tunnels, simulation of the detonation of nuclear weapons, and research into nuclear fusion), cryptanalysis, and the like. Major universities, military agencies and scientific research laboratories are heavy users.

DESIGN

*Supercomputers using custom CPUs traditionally gain their speed over conventional computers through the use of innovative designs that allow them to perform many tasks in parallel, as well as complex detail engineering. They are used for certain types of computation, usually numerical calculations, and perform poorly at more general computing tasks. Their memory hierarchy is very carefully designed to ensure the processor is kept fed with data and instructions at all times – in fact, much of the performance difference between slower computers and supercomputers is due to the memory hierarchy. Their I/O systems tend to be designed to support high bandwidth, because supercomputers are not used for transaction processing.

Amdahl's law applies here as with all highly parallel systems, and supercomputer designers make great efforts to eliminate software serialization, and use hardware to accelerate the remaining bottlenecks.*

SUPERCOMPUTER CHALLENGES

A supercomputer generates large amounts of heat and must be cooled. Cooling most supercomputers is a major HVAC problem. Information cannot move faster than the speed of light between two parts of a supercomputer. For this reason, a supercomputer that is many meters across must have latencies between its components measured at least in the tens of nanoseconds.

Vocabulary Notes

1.to gain – to get – to obtain

2.to eliminate – to exclude

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POST – READING TASK (to be done in writing)

I. Give examples of highly calculation-intensive tasks.

II. Write a summary by formulating sentences with the key words.

1.highly calculationintensive tasks

2.heavy users

3.gain their speed through

4.to be used for certain types of computation

5.to be carefully designed

6.the performance difference

7.to make great efforts

8.a major problem

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PART II

COMPUTER SECURITY TECHNOLOGY

UNIT I

CRYPTOGRAPHY

PRE-READING TASK Study some grammar points.

I. S + is supposed (is considered, is believed, is supposed, is expected, is assumed) + to V can be used in this way. These verbs express generally accepted opinion and correspond to Russian –

Считают, что; Полагают, что; Ожидают, что; Допускают, что

I. We use two variants.

1.It is considered that cryptography is a science of protecting information by encoding it into an unreadable format.

2.Cryptography is considered to be a science of protecting information by encoding it into an unreadable format.

You can also use these structures with:

is found = найдено, что; is said = говорят, что; is known =

известно, что; is proved = доказано, что

Study the sentences.

1.Cooling supercomputers is considered to be the major problem.

2.All computers are known to differ only in speed and memory capacity.

3.Chess programs are supposed to be able to defeat over 99% of all human players.

4.Computer vendors are looking for a product or strategy that can compete with the Wintel standard, and Java is believed to be such a product.

II. The participle

When two things happen at the same time, you can use Ving for one of the verbs.

We can also use Ving or V3 after while or when (which are not translated). These structures are used mainly in written English.

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Study the sentence.

When carried out by the “good guys”, cryptanalysis is intended to identify flaws and weaknesses.

Give Russian correspondence:

to cause (to bring about), a way (a method), so (therefore), too + adj.

INFORMATION PROTECTING

Study the passage.

Computer hackers – people who illegally access computer systems – often violate privacy and can destroy records. Programs called viruses or worms can replicate and spread from computer to computer, erasing information or causing computer malfunctions or failure.

Cryptography is considered to be a science of protecting information by encoding it into an unreadable format. Cryptography is an effective way of protecting sensitive information stored on media or transmitted through confidential network communication paths. One of the goals of cryptography, and the mechanisms that make it up, is to hide information from unauthorized individuals. However, with enough time, resources, and motivation, hackers can break most algorithms and reveal the encoded information. So a more realistic goal of cryptography is to make obtaining the information too work – intensive and time consuming to be worthwhile for a hacker. With the birth of the internet, encryption has become an integrated part of the computing world.

Encryption is used in hardware devices and in software to protect data, banking transactions, corporate extranet transmissions, e-mail messages, web transactions, wireless communications, confidential information, faxes, and phone calls. The code breakers and cryptanalysis efforts and the amazing number-crunching capabilities of the microprocessors hitting the market each year have quickened the evolution of cryptography.

Cryptanalysis is an important part of cryptography. It is the science of studying and breaking the secrecy of encryption processes. When carried out by the “good guys”, cryptanalysis is intended to identify flaws and weaknesses so that developers can go back to the drawing board and improve the components. It is also performed by motivated

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hackers to identify the same types of flaws, but with the goal of obtaining the encryption key for unauthorized access to confidential information.

Vocabulary Notes

1.to access computer information – to retrieve information out of a computer

2.to violate privacy – to disturb

3.to erase information – to destroy

4.a malfunction – an error – a failure

5.to encrypt – to code – to encode

6.a medium (media) – a carrier of information

7.to authorize –to allow

8.to reveal – to disclose

9.to be worthwhile – to be profitable

10.an integrated part – one of the basic parts

11.number-crunching capabilities – fast processing of big amounts of information

12.to be intended for – to be designed for

13.a flaw – a defect

POST-READING TASK (to be done in writing)

Formulate some sentences to cover the points:

CLASS EXERCISES

Exercise 1 (in groups)

Checking up understanding (in pairs)

1.What is cryptography?

2.Is cryptography considered to be a science?

3.What is one of the goals of cryptography?

4.Is this goal realistic? Why?

5.What is a more realistic goal?

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6.Where is encryption used? What is it used for?

7.What is cryptanalysis?

8.What is cryptanalysis intended for when carried out by “good”

guys?

9.What goals do hackers have when performing cryptanalysis?

Exercise 2 (do it yourself)

Make up simple sentences in the passive with the below expressions. Follow the passage.

Model: The information is protected by encoding it into an unreada-

UNIT 2

PUBLIC KEY CRYPTOGRAPHY

PRE-READING TASK Study some grammar points.

I one(s) is used to refer to a thing) that has been mentioned before.

Study the sentences.

1.The public-key system works on a principle of a safe with two keys, one public key to lock it, and one private one to open it.

2.A Turing machine is one that can compute the answers to a mathematical problem based on a program.

II that (those) is also used to refer to a thing (things) that has been mentioned before.

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