Английский язык для пользователей ПК и программистов - Гольцова Е.В.
ISBN 5-7931-0086-5
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К. in most text 11. встречаться с различной частотой
L. occur with different frequences 12. встречаются реже
М. for commoner sections 13. тем не менее
N. occur less often 14. больше, чем
О. clearly 15. меньше, чем
P. less than 16. соответствующий
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Q. more than R. however
S. for space to be saved
17. внутриофисные документы
18. предположим
19. чтобы сохранить пространство
Упражнение 13. Translate, paying attention to the suffixes: Переведите, обращая внимание на суффиксы:
permit, permutation, permittance achieve, achievement identity, identify allocate, allocation treat, treatment, treaty jnormal, normally number, numberless susceptibility, susceptible , long, longer, length fine, finest
frequency, frequencies Упражнение 14. Translate and name the auxiliary verbs:
Переведите и выделите вспомогательные глаголы для каждого из сказуемых:
to compress: compresses, аш compressing, compressed, have compressed; to allocate: can allocate, allocated, allocating; to treat: treats, treated, is treated, were treated: to achieve: achieved, bas achieved, achieves, achieving.
Упражнение 15. Look through text II and mark all comparitives.
Просмотрите Текст II и отметьте все случаи использования степеней сравнения прилагательных.
Упражнение 16. Look through the definition of "code" and match it with the corresponding Russian word:
Просмотрите определение понятия «код» и сопоставьте каждое значение с соответствующим русским:
First, the phrases:
a set of rules набор правил
defining the way определяющий способ
bits can be arranged биты могут быть организованы
to represent numbers представлять числа
uses a type of codes использует типы кодов
to assign meanings to приписывать значения
to represent a larger item of data представлять больший набор данных less storage space меньше пространства памяти
151 Английский для пользователей ПК
NoW the definition: CODE is:
1. a set of rules defining the way in which bits can be arranged to represent numbers, letters, and special symbols: each computer uses a type of code, such as ASCII or EBCDIC;
2. to assign meanings to a set of numbers, letters, or special symbols;
3. to write a program
4. one or more instructions in a program
5. assigning a character to represent a larger item of data so that less storage space is used, as in assigning the number one to mean college graduate two for high school graduate, and so on.
кодировать —_
кодировка —_
код —_
(машинное) слово (например, команда) —_
программировать —_
Упражнение 17. Read the text very carefully: Прочтите текст очень внимательно:
Text II
FIXED-LENGTH ONTO FIXED-LENGTH MAPPING Our first category of methods compresses by mapping fixed-length portions of the input file onto fixed -length codes. Clearly, for space to be saved, the number of bits per character in the output file must be less than in the input file.
A typical computer system uses an 8-bit byte for each character in a text file. In theory this permits a 256-character alphabet. However, for some types of file, for example program source files or inter-office memos, a much smaller alphabet may be adequate. Thus we might compress simply by allocating smaller fixed-length codes to fixed size units of the input file.
Suppose our input file has a 30-character alphabet; perhaps we are compressing mailgrams with only a few symbols in addition to the upper case letters. We can allocate each character a 5-bit code, pack three characters into a 16-bit word that normally only holds two and compress a file to two-thirds its size.
In general, the compressed units can be N-character segments of the input file. Suppose, for example, that our input file uses a 40-character alphabet. Compressing a character at a time means that each requires 6 bits
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and we can still hold only two in a 16-bit word. However, we can treat a 3-character section of the file as a base 40 number and represent it by the corresponding binary value. There are 40 x 40 x 40 = 64,000 combinations of three characters; this value is just small enough to fit into a 16-bit word. However, we can treat a 3-character section of the file as a base 40 number and represent it by the corresponding binary value. There are 40 x 40 x 40 = 64,000 combinations of three characters; this value is just small enough to fit into a 16-bit word (0-65, 535). Thus a file with a 40-character alphabet can also be compressed to two-thirds its normal size.
Standard FORTRAN-77 requires only 49 characters (digits, upper case letters, and 13 special characters = + -*/ ()»¦$': and space) . Using either of the techniques above we can pack five characters into a 32-bit word. Using an 8-bit code we could only pack four characters, thus we can compress a FORTRAN-7 7 text to 80% of normal size. In most text, input sections occur with different frequencies, for example, in English, we" is more common than "x". We may achieve a greater degree of compression by having shorter output codes for commoner sections and longer codes for those that occur less often. In the next section we look at methods that use variable-length output codes.
