- This page last updated on 11 March 2024
Because computers are made up of digital electronics, internally they respond to two kinds of electrical states: "on" or "off". These may actually be high or low voltage, positive and negative voltage, or some other combination. The key is that there are only two conditions. We represent these two conditions with two numbers: 0 and 1.
Computers use BITS (short for Binary Digits) to represent information in digital form. A computer BIT is a binary value. BITS have a value of either 1 or 0. The only Digits in the Binary system are 0 and 1.
Strings of BITS are used to represent numbers larger than 1.
BITS in strings of eight are called BYTES, and one BYTE usually represents a single character of data in the computer.
Example: One BYTE (consiting of 8 BITS) for the capital letter A is 01000001 and for the small letter a is 01100001
One BYTE can have 256 different values
Convert 01000001 Binary to Decimal and you get 65, which the computer will interpret as the letter A.
The higest number you can have with one BYTE is 11111111 or 255
It is easy to get confused over the point of zero being a digit. A byte with all digits ON represents the decimal number 255 and it is hard to visualize this as the 256th digit in a series, but that is exactly what the computer demands of you.
In brief -- start learning to count from zero, not one!
One byte works well for individual characters, but computers are also good at manipulating numbers.
Integers are typically stored with either 4 or 8 bytes
4 bytes can store numbers between -2147483648 and 2147483647
8 bytes can store numbers between -9223372036854775808 and 9223372036854775807
There is another number system that is used with computers called HEXADECIMAL. Hexadecimal is a Base 16 number system and uses numbers and letters to represent its 16 differnet digets: 0 1 2 3 4 5 6 7 8 9 A B C D E F.
The biggest advantage of hexadecimal number is that it is really compact. They can represent a number in the least amount of characters. Binary includes just zeros and ones and for that reason, to represent a number in binary takes eight times more numbers than the hexadecimal numbers. Another reason 16 is a power of 2 and easily converted.
The first place we will use the concept of counting in binary is in talking about computer memory. Early manufacturers stated memory capacity in terms of KILOBYTES. In the decimal system, the prefix kilo- means 1,000. In the binary system the prefix kilo- means 1,024.
Why 1024? In Binary 2 to the 10th power is 2024.
The International System of Units (SI), commonly known as the metric system, is the international standard for measurement. This is where the term KILO (1000) comes from.
In 1998 the International Electrotechnical Commission (IEC) and other regulatory organizations banded together to create a new set of prefixes to be used for information storage to be used in lieu of the SI ones. Enter binary prefixes.
So now we use a new prefix.
Under the old system a computer may be described as having 640K (640 kilobytes) of memory, when it really has 640 x 1,024 or 655,360 bytes.
Enter binary prefixes. By replacing the last two letters at the end of the old prefixes with a -bi. Under the New System this computer would now have 640 KIBIBYTES.
One kibibyte equals 2 to the 10th power, or 1,024 bytes.
One mebibyte equals 2 to the 20th power, or 1,048,576 bytes.
One gibibyte equals 2 to the 30th power, or 1,073,741,824 bytes.
One tebibyte equals 2 to the 40th power, or 1,099511,627,776 bytes.
One pebibyte equals 2 to the 50th power, or 1,125,899,906,842,624 bytes.
One exbiyte equals 2 to the 60th power, or 1,152,921,504,606,846,976 bytes.
One zebiabyte equals 2 to the 70th power, or 1,180,591,620,717,411,303,424 bytes
One yobiabyte equals 2 to the 80th power, or 1,208,925,819,614,629,174,706,176 bytes
Some other units of measurement you may come across:
Frequency Multipliers
HZ - Hertz - Cycles Per second
KHZ - Kilohertz - one thousand hertz
MHZ - Megahertz - one million hertz
GHZ - gigahertz - one billion hertz
THZ - Terahertz - one trillion hertz
Radio Frequency Bands
Extremely Low Frequency - ELF - Frequency 3 to 30 HZ - Wavelength: 100,000 to
10,000 KM
Super Low Frequency - SLF - 30-300 HZ; 10,000-1,000 KM
Ultra Low Frequency - ULF - 300-3000 HZ; 1,000-100 KM
Very Low Frequency - VLF - 3-30 KHZ; 100-10 KM
Low Frequency - LF - 30-300 KHZ; 10-1 KM
Medium Frequency - MF - 300-3000 KHZ; 1 KM - 100 M
High Frequency - HF - 3-30 MHZ; 100-10 M
Very High Frequency - VHF - 30-300 MHZ; 10-1 M
Ultra High Frequency - UHF - 300-3000 MHZ; 1M - 10CM
Super High Frequency - SHF - 3-30 GHZ; 10-1 CM
Extremely High Frequency - EHF - 30-300 GHZ; 1 CM - 1 MM
The wavelength of a radio frequency (sinusoidal wave) is the distance between consecutive corresponding points of the same phase; or to make it simple. Peak to Peak distance. The Wavelength of any frequency can be found by the formula: velocity divided by frequency. Velocity is fixed at the speed of light: 300,000 kilometres per second. That is why your VHF TV antenna is larger than your UHF TV antenna. The higher the frequency the shorter the wavelength. Antennas must be designed so that the elements of the antenna fit into the wavelength of the frequency being transmitted. Some antennas are quarter-wave or half-wave antennas because it would be impossible to build an antenna to exactly match the lower frequencies. This is a simple explanation, for a more detailed description, take a look at Wikipedia "Wavelength".
- This page last updated on 11 March 2024