Lesson 1: Computer Communication
In this lesson, we examine the fundamentals of electronic communication and explore how computer communication differs from human communication.
After this lesson, you will be able to:Estimated lesson time: 20 minutes
- Understand how a computer transmits and receives information.
- Explain the principles of computer language.
Early Forms of Communication
Humans communicate primarily through words, spoken and written. From ancient times until about 150 years ago, messages were either verbal or written in form. Getting a message to a distant recipient was often slow, and sometimes the message (or the messenger) got lost in the process.
As time and technology progressed, people developed devices to communicate faster over greater distances. Items such as lanterns, mirrors, and flags were used to send messages quickly over an extended visual range.
All "out of earshot" communications have one thing in common: they require some type of "code" to convert human language to a form of information that can be packaged and sent to the remote location. It might be a set of letters in an alphabet, a series of analog pulses over a telephone line, or a sequence of binary numbers in a computer. On the receiving end, this code needs to be converted back to language that people can understand.
Dots and Dashes, Bits and Bytes
Telegraphs and early radio communication used codes for transmissions. The most common, Morse code (named after its creator, Samuel F. B. Morse), is based on assigning a series of pulses to represent each letter of the alphabet. These pulses are sent over a wire in a series. The operator on the receiving end converts the code back into letters and words. Morse code remained in official use for messages at sea almost to the end of the twentieth century—it was officially retired in late 1999.
Morse used a code in which any single transmitted value had two possible states: either a dot or a dash. By combining the dots and dashes into groups, an operator was able to represent letters, and by stringing them together, words. That form of on-off notation can also be used to provide two numbers, 0 and 1. Zero represents no signal, or off; and one represents a signal, or on, state.
This type of number language is called binary notation because it uses only two digits, usually 0 and 1. It was first used by the ancient Chinese, who used the terms yin (empty) and yang (full) to build complex philosophical models of how the universe works.
Our computers are complex switch boxes that have two states and use a binary scheme as well. The value of a given switch's state—on or off—represents a value that can be used as a code. Modern computer technology uses terms other than yin and yang, but the same binary mathematics creates virtual worlds inside our modern machines.
The Binary Language of Computers
The binary math terms that follow are fundamental to understanding PC technology.
Bits
A bit is the smallest unit of information that is recognized by a computer: a single on/off event.
Bytes
A byte is a group of eight bits. A byte is required in order to represent one character of information. Pressing one key on a keyboard is equivalent to sending one byte of information to the CPU (the computer's central processing unit). A byte is the standard unit by which memory is measured in a computer—values are expressed in terms of kilobytes (KB) or megabytes (MB). The table that follows lists units of computer memory and their values.
| Memory Unit | Value |
|---|---|
| Bit | Smallest unit of information, shorthand term for binary digit |
| Nibble | 4 bits (Half of a byte) |
| Byte | 8 bits (Equal to one character) |
| Word | 16 bits on most personal computers (longer words possible on larger computers) |
| Kilobyte (KB) | 1024 bytes |
| Megabyte (MB) | 1,048,576 bytes (Approximately one million bytes or 1024 KB) |
| Gigabyte (GB) | 1,073,741,824 bytes (Approximately one billion bytes or 1024 MB) |
The Binary System
The binary system of numbers uses the base of 2 (0 and 1). As described earlier, a bit can exist in only two states, on or off. When bits are represented visually:
- 0 (zero) equals off.
- 1 (one) equals on.
The following is one byte of information in which all eight bits are set to zero. In the binary system, this sequence of eight zeros represents a single character—the number 0.
0 0 0 0 0 0 0 0 |
The binary system is one of several numerical systems that can be used for counting. It is similar to the decimal system, which we use to calculate everyday numbers and values. The prefix "dec" in the term "decimal system" comes from the Latin word for ten and denotes a base of ten. That is, the decimal system is based on the ten numbers zero through nine. The binary system has a base of two, the numbers zero and one.
Counting in Binary Notation
Every schoolchild learns to count using the decimal system. There, the rightmost whole number (the number to the left of the decimal point) is the "digits" column. Numbers written there have a value of zero to nine. The number to the left of the digits column (if present) is valued from ten to ninety—the "tens" column. Ten is the factor of each additional row in the decimal system of notation. To get the total value of a number, we add together all columns in both systems: 111 is the sum of 100+10+1.
NOTE
A factor is an item that is multiplied in a multiplication problem. For example, 2 and 3 are factors in the problem 2 × 3.
In our more common decimal notation, the values of numbers are founded on a base of ten, starting with the rightmost column. Any number in that position can have a value ranging from zero to nine. In the next column to the left, the values range from 10 to 99; and in the column to the left of that, values range from 100 to 999. Binary notation uses a system of right-to-left columns of ascending values, but in which each row has only two-instead of 10-possible numbers.
Under the binary system, the first row to the right can be only zero or one; the next row to the left can be two or three (if a number exists in that position). The columns that follow have values of four, then eight, then sixteen, and so on, each column doubling the possible value of the one to its right. Two is the factor used in the binary system, and—just like decimal—zero is a number counted in that tally. Examples of bytes of information (eight rows) follow.
Byte—Example A
The value of this byte is zero because all bits are off (0 = off).
0 0 0 0 0 0 0 0 8 bits 128 64 32 16 8 4 2 1 # values |
Byte—Example B
In this example, two of the bits are turned on (1 = on). The total value of this byte is determined by adding the values associated with the bit positions that are on. This byte represents the number 5 (4 + 1).
0 0 0 0 0 1 0 1 8 bits 128 64 32 16 8 4 2 1 # values |
Byte—Example C
In this example, two different bits are turned on to represent the number 9 (8 + 1).
0 0 0 0 1 0 0 1 8 bits 128 64 32 16 8 4 2 1 # values |
Those who are mathematically inclined will quickly realize that 256 is the largest number that can be represented by a single byte.
Because computers use binary numbers and humans use decimal numbers, A+ technicians must be able to perform simple conversions. The following table shows decimal numbers and their binary equivalents (0 to 9). You will need to know this information. The best way to prepare is to learn how to add in binary numbers, rather than merely memorizing the values.
| Decimal Number | Binary Equivalent |
|---|---|
| 0 | 0000 |
| 1 | 0001 |
| 2 | 0010 |
| 3 | 0011 |
| 4 | 0100 |
| 5 | 0101 |
| 6 | 0110 |
| 7 | 0111 |
| 8 | 1000 |
| 9 | 1001 |
Numbers are fine for calculating, but today's computers must handle text, sound, streaming video, images, and animation as well. To handle all of that, standard codes are needed to translate between binary machine language and the type of data being represented and presented to the human user. The first common code-based language was developed to handle text characters.
Parallel and Serial Devices
The telegraph and the individual wires in our PCs are serial devices. This means that only one element of code can be sent at a time. Like a tunnel, there is only room for one person to pass through at one time. All electronic communications are—at some level—serial, because a single wire can have only two states: on or off.
To speed things up, we can add more wires. This allows simultaneous transmission of signals. Or, to continue our analogy, it's like adding another set of tunnels next to the first one; we still have only one person per tunnel, but we can get more people through because they are traveling in parallel. That is the difference between parallel and serial data transmission. In PC technology, we often string eight wires in a parallel set, allowing eight bits to be sent at once. This means that a single "send" can represent up to 256 numbers 28 = 256. That is the same number of values found in the ASCII code system (discussed in the next paragraph). Figure 2.1 illustrates serial and parallel communication.
Figure 2.1 Serial and parallel communication
ASCII Code
The standard code for handling text characters on most modern computers is called ASCII (American Standard Code for Information Interchange). The basic ASCII standard consists of 128 codes representing the English alphabet, punctuation, and certain control characters. Most systems today recognize 256 codes: the original 128, plus an additional 128 codes called the extended character set.
Remember that a byte represents one character of information; four bytes are needed to represent a string of four characters. The following four bytes represent the text string 12AB (using ASCII code):
00110001 00110010 01000001 01000010 1 2 A B |
The following illustrates how the binary language spells the word "binary":
B I N A R Y 01000010 01001001 01001110 01000001 01010010 01011001 |
NOTE
It is very important to understand that in computer processing the "space" is a significant character. All items in a code must be set out for the machine to process. Like any other character, the space has a binary value that must be included in the data stream. In computing, the absence or presence of a space is critical and sometimes causes confusion or frustration among new users. Uppercase and lowercase letters also have different values. Some operating systems (for example, UNIX) distinguish between them for commands, while others (for example, MS-DOS) translate the uppercase and lowercase into the same word no matter how it is cased.
The following table is a complete representation of the ASCII character set. Even in present-day computing, laden with multimedia and sophisticated programming, ASCII retains an honored and important position.
| Symbol | Binary 1 Byte | Decimal | Symbol | Binary 1 Byte | Decimal |
|---|---|---|---|---|---|
| 0 | 00110000 | 48 | V | 01010110 | 86 |
| 1 | 00110001 | 49 | W | 01010111 | 87 |
| 2 | 00110010 | 50 | X | 01011000 | 88 |
| 3 | 00110011 | 51 | Y | 01011001 | 89 |
| 4 | 00110100 | 52 | Z | 01011010 | 90 |
| 5 | 00110101 | 53 | A | 01100001 | 97 |
| 6 | 00110110 | 54 | B | 01100010 | 98 |
| 7 | 00110111 | 55 | C | 01100011 | 99 |
| 8 | 00111000 | 56 | D | 01100100 | 100 |
| 9 | 00111001 | 57 | E | 01100101 | 101 |
| A | 01000001 | 65 | F | 01100110 | 102 |
| B | 01000010 | 66 | G | 01100111 | 103 |
| C | 01000011 | 67 | H | 01101000 | 104 |
| D | 01000010 | 68 | I | 0110100 | 105 |
| E | 01000101 | 69 | J | 01101010 | 106 |
| F | 01000110 | 70 | K | 01101011 | 107 |
| G | 01000111 | 71 | L | 01101100 | 108 |
| H | 01001000 | 72 | M | 01101101 | 109 |
| I | 01001001 | 73 | N | 01101110 | 110 |
| J | 01001010 | 74 | O | 01101111 | 111 |
| K | 01001011 | 75 | P | 01110000 | 112 |
| L | 01001100 | 76 | Q | 01110001 | 113 |
| M | 01001101 | 77 | R | 01110010 | 114 |
| N | 01001110 | 78 | S | 01110011 | 115 |
| O | 01001111 | 79 | T | 01110100 | 116 |
| P | 01010000 | 80 | U | 01110101 | 117 |
| Q | 01010001 | 81 | V | 01110110 | 118 |
| R | 01010010 | 82 | W | 01110111 | 119 |
| S | 01010011 | 83 | X | 01111000 | 120 |
| T | 01010100 | 84 | Y | 01111001 | 121 |
| U | 01010101 | 85 | Z | 01111010 | 122 |
NOTE
All letters have a separate ASCII value for uppercase and lowercase. The capital letter "A" is 65, and the lowercase "a" is 97.
Keep in mind that computers are machines, and they do not really perceive numbers as anything other than electrical charges setting a switch on or off. Like binary numbers, electrical charges can exist in only two states—positive or negative. Computers interpret the presence of a charge as one and the absence of a charge as zero. This technology allows a computer to process information.
Lesson Summary
The following points summarize the main elements of this lesson:
- Computers communicate using binary language.
- A bit is the smallest unit of information that is recognized by a computer.
- ASCII is the standard code that handles text characters for computers.
EAN: N/A
Pages: 127