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Information is a set of marks or signs that have meaning. These consist of letters or numbers, digits or characters, typewriter signs, other kinds of signs, and so on. A computer reacts differently to different digits or characters, and reacts to them as units that have meaning. For example, information for an analog computer has to be in the form of distances, or rotations, or voltages, or other physical variables. And for a digital computer information has to be in the form of digits or numbers.
Any information may be represented by the binary system including two digits: one (1) and zero (0). Each I and 0 is a separate binary digit called a bit. A bit is the smallest part of information. Bits are typically grouped in units that are called bytes. A byte is the basic unit of information used in modern computers and consists of eight bits.
The bytes are handled usually in standard groups called machine words or just words. There are two basic types of information or words that can be put into a memory cell or location, words that are numerical quantities and words that are computer instructions. Regularly, an instruction to the machine is expressed as a word; and so the same set of characters may have meaning sometimes as a number, sometimes as an instruction. A speed of 96,000 characters per second is the same as a speed of 8,000 words per second. Most human beings could not take even 12-digit number per second.2
Physically the set of bits is a set of arrangements of some physical equipment. One of the ways of storing information in a computer is storing by using a set of small magnetically polarized spots on a magnetic surface.
The computer is told what operations to perform by means of instructions. An instruction is a command to the computer. It consists of a verb (an operational code) and a noun (an operand). For example, if the computer is instructed "Add 365 the number of times stated in the register R", and if the register R stores the code for number 3, then the computer will perform that operation three times. An instruction word looks like a number, and there is no way to tell from the word itself whether it is a quantity or an instruction. The computer must be told exactly which address contains an instruction and which contains a quantity.
An address is the name of particular memory location or cell. Each memory location (word or byte) has its own unique address or number just like a post office box.3 For example, if the computer contains 100 memory cells, their respective addresses might be the numbers 4 from 1 to 100 (or 0 through 99). And instead of saying "A word is in a memory cell", the computer personnel say, "The contents of an address is a word."
Reasonable operations are mathematical and logical. Mathematical operations include arithmetic and algebraic operations. Arithmetic operations are addition, subtraction, multiplication, division, taking a square root, etc.; and algebraic operations are called raising to a power as well as differentiating and integrating.
Logical operations include comparing, selecting, sorting, matching, etc. These are operations which may be performed either on numbers, or on expressions consisted of letters such as ordinary words. A very important logical operation performed by a computer is determining, i.e., which of two operations is to be performed next.
ИНФОРМАЦИЯ, МАШИННЫЕ СЛОВА, КОМАНДЫ, АДРЕСА И РАЦИОНАЛЬНЫЕ ОПЕРАЦИИ
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Personal computer
A personal computer (PC) is a computer whose original sales price, size, and capabilities make it useful for individuals.
A personal computer may be a home computer, or may be found in an office, often connected to a local area network. The distinguishing characteristic is that the computer is used only (or mostly) by one person at a time, in a very interactive fashion, with no significant delay between an operator action and response by the computer. This is opposite to the batch processing or time-sharing models which allowed large expensive systems to be used by many people, usually at the same time.
The capabilities of a personal computer have changed greatly since the introduction of electronic computers. By the early 1970's, people in academic or research institutions had the opportunity for single-person use of a computer system in interactive mode for extended durations, although these systems would still have been too expensive to be owned by a single individual. The introduction of the microprocessor, a single chip with all the circuitry that formerly occupied large cabinets, lead to the proliferation of personal computers after about 1975. Early personal computers generally called microcomputers, sold often in kit form and in limited volumes and were of interest mostly to hobbyists and technicians. By the late 1970's, mass-market pre-assembled computers allowed a wider range of people to use computers, focusing more on software applications and less on development of the processor hardware. Throughout the 1970's and 1980's, home computers were developed for household use, offering some personal productivity, programming and games, while somewhat larger and more expensive systems (although still low-cost compared with minicomputers and mainframes) were aimed for office and small business use.
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