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Counting: introduction
1. Bits and bytes
Inside the computer are bits and bytes. To really understand what is going on, you need to know something about bits and bytes.
2. Bits
A
bit, for binary digit, can represent two values.
The two values of a bit are often written as
0 and
1.
You cannot actually see a
0 or
1 inside a computer.
How are the
2 values of a bit represented?
3. Bit as binary digit
John Tukey (American mathematician and statistician) , working with John von Neumann, coined the term "
bit" as "
binary digit". The classical "
bit" has one of two values, which can be represented as
0 (usually taken as
false) and
1 (usually taken as
true).
The term "
bit" was first used in an article by Claude Shannon in 1948.
4. Two values
Here are some ways to represent
2 values of a bit.
low or high voltage level
low or high light level
low or high magnetic field
low or high reflection level
5. CD ROM
A original standard
CD (Compact Disc) can hold 650 MB of data, or about 5 billion bits. Each bit is either a burned hole or not a burned hole at a certain position on the CD that either reflects light or does not reflect light. That is how the 5 billion bits are created and accessed.
6. Byte
7. Bytes
A byte is made up of 8 bits.
Question: How many values can a byte represent?
8. Values of a byte
A
byte can represent
256 values.
Since each bit can represent
2 values,
8 bits can represent
256 values as follows.
2*2*2*2*2*2*2*2 = 28 = 256
9. Nibble
A nibble is half a byte
Yes, the technical term for four bits, or half a byte, is a nibble.
A group of 4 bits make a nibble that can represent 16 values.
A hexadecimal digit represents one nibble, or 4 bits.
Computer engineers are often concerned with the upper nibble (upper 4 bits) and lower nibble (lower 4 bits) of a byte.
10. Words
A group of 16 bits (i.e., 2 bytes) is called a word or WORD.
A group of 32 bits is called a dword, for double-word or DWORD.
A group of 64 bits is called a qword, for quad-word or QWORD.
11. End of page
