Cache memory

1. Most PCs are held back not by the speed of their main processor, but by the time it takes to move data in and out of memory. One of the most important techniques for getting around this bottleneck is the memory cache.

2. The idea is to use a small number of very fast memory chips as a buffer or cache between main memory and the processor. Whenever the processor needs to read data it looks in this cache area first. If it finds the data in the cache then this counts as a 'cache hit' and the processor need not go through the more laborious process of reading data from the main memory. Only if the data is not in the cache does it need to access main memory, but in the process it copies whatever it finds into the cache so that it is there ready for the next time it is needed. The whole process is controlled by a group of logic circuits called the cache controller.

3. One of the cache controller's main jobs is to look after “cache coherency” which means ensuring that any changes written to main memory are reflected within the cache and vice versa. There are several techniques for achieving this, the most obvious being for the processor to write directly to both the cache and main memory at the same time. This is known as a “write-through” cache and is the safest solution, but also the slowest.

4. The main alternative is the “write-back” cache which allows the processor to write changes only to the cache and not to main memory. Cache entries that have changed are flagged as “dirty”, telling the cache controller to write their contents back to main memory before using the space to cache new data. A write-back cache speeds up the write process, but does require a more intelligent cache controller.

5. Most cache controllers move a “line” of data rather than just a single item each time they need to transfer data between main memory and the cache. This tends to improve the chance of a cache hit as most programs spend their time stepping through instructions stored sequentially in memory, rather than jumping about from one area to another. The amount of data transferred each time is known as the “line size”.

Questions:

1. What is the memory cache? 2. In what case does the processor need to access main memory? 3. What is one of the cache controller's main jobs? 4. What is known as a “write-through” cache? 5. What is the main alternative to a “write-through” cache?

II. Перепишите и письменно переведите 2 и 3 абзацы текста.

III. Определите тип условных предложений и письменно переведите их, обращая внимание на разницу в переводе форм сослагательного наклонения во II, III типах условных предложений и форм изъявительного наклонения в предложениях I типа.

It would be difficult to enumerate all the fields of computer applications. 2. We shall begin the meeting as soon as everybody comes. 3. If more than three variables were involved, the graphical representation would not be possible. 4. If he had been given opportunity, the work might have been finished. 5. If he were more careful, he would have given a correct answer. 6. Had they been asked to take part in the research, they would have agreed. 7. But for the paradoxes, Cantor’s set theory could have served as a secure foundation for maths.

IV. Определите тип условных предложений. Выберите правильный вариант формы глагола. Письменно переведите предложения.

1. We shall perform all the necessary operations provided you (will help/ help/helped) us. 2. If we had our first examination tomorrow, we (should have/shall have/have) more time to prepare for the second one. 3. If he (has/had/had had) time yesterday, he would have completed the experiment. 4. If he had worked harder last year, he (won’t have/wouldn’t have/doesn’t have) any difficulties with his exams now. 5. (Were/Had/Will be) I asked how many transfinite numbers exist, I would say that there exists an infinity of transfinite cardinal numbers. 6. If it (hadn’t been/were not/had been) for her help, he wouldn’t have made that great discovery.

V. Выберите правильный вариант формы глагола в сослагательном наклонении в конструкциях, содержащих wish/if only. Письменно переведите предложения.

1. I wish I (could/can/shall) define that concept with the aid of definition. 2. We wish the problem (will be/were/has been) more investigated. 3. He wished he (doesn’t create/shouldn’t create /had not created) a false impression that all sequences were of the same type. 4. They wish hackers (will not break/would not break /have not broken) into corporate and government computers. 5. If only I (had defined/define/will define) all sequences explicitly! 6. If only he (were pleased/ is pleased/will be pleased) with my work!

VI. Переведите письменно предложения, учитывая способы перевода придаточных предложений и оборотов, содержащих формы сослагательного наклонения.

1. I’d rather define the complement of the set X with respect to the set Y. 2. You’d better begin the analysis by defining this number. 3. It’s time we thought about the matter. 4. It’s very important in some cases that there should exist an algebraic equation connecting x and y. 5. He insists that every student should realize that one-to-one correspondence lies at the heart of Cantor’s set theory. 6. Classical Greek mathematicians avoided infinite processes as if they had not existed at all. 7. Make haste lest you should be late.

VII. Выберите правильный вариант и письменно переведите предложения, содержащие формы сослагательного наклонения.

1. I (would better/would rather/had rather) consider exact decimals in this specific example. 2. You (had better/would better/would rather) introduce these definitions for easy reference. 3. It’s time you (finished/finish/will finish) writing the test. 4. It is always recommended that we (should limit/would limit/limited) the domain of a particular function. 5. Cantor insisted that the number properties of infinite sets (should be/would be /will be) different from those of finite sets.

VIII. Переведите письменно предложения, обращая внимание на то, как переводятся модальные глаголы в сочетании с перфектными формами инфинитива.

1. They must have found a good approximation for the solution. 2. They must have been discussing the question for two hours now. 3. They may have proved this theorem with the help of this axiom. 4. The graph may have been sketched incorrectly. 5. You might have noticed that all notations used in this text are consistent. 6. They ought to have given the necessary explanation.