Computers store data using the binary system. This is based on the number 2 and numbers in the system use the digits 0 and 1. That is 2 digits in all. Like a decimal, each place (or column) in a number can be represented by a power. In this case it is a power of 2 as the system is 2 based. An example of a 2 based number is 101. This can be thought of as: 1 four, plus 0 twos, plus 1 one.The table below shows how this can be represented.

Its decimal equivalent is: 15 = 1x8 + 1x4 +1x2 + 1x1

or: 24 - 1 (16 - 1 = 15)

Using 4 bits there are 24 (16) different combinations of zeros and ones, 0000 being the smallest and 1111 the largest. There is a simple formula to work out the largest decimal number that can be represented by a certain number of bits all set to 1. It is 2 to the power of the number of bits minus 1. One is taken off because the system starts at 0. So, using four bits the following decimal numbers can be represented: 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. This is sixteen numbers in all.

Particular bit patterns have names. Four bits is called a nibble, eight bits is called a byte, four bytes is called a word. Using the formula above a byte can represent a maximum decimal value of 28 - 1, or 255.

or: 24 - 1 (16 - 1 = 15)

Using 4 bits there are 24 (16) different combinations of zeros and ones, 0000 being the smallest and 1111 the largest. There is a simple formula to work out the largest decimal number that can be represented by a certain number of bits all set to 1. It is 2 to the power of the number of bits minus 1. One is taken off because the system starts at 0. So, using four bits the following decimal numbers can be represented: 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. This is sixteen numbers in all.

Particular bit patterns have names. Four bits is called a nibble, eight bits is called a byte, four bytes is called a word. Using the formula above a byte can represent a maximum decimal value of 28 - 1, or 255.

Different systems within a computer can use different numbers of bits. For example, most modern processors can read/write 64 bits of data at a time from/to RAM, whereas the Windows 7 operating system comes in both 32 and 64 bit versions. For various reasons the 32 bit version limits the amount of RAM it can address to around 3 Gigabytes, so anything above this figure is useless.Different systems within a computer can use different numbers of bits. For example, most modern processors can read/write 64 bits of data at a time from/to RAM, whereas the Windows 7 operating system comes in both 32 and 64 bit versions. For various reasons the 32 bit version limits the amount of RAM it can address to around 3 Gigabytes, so anything above this figure is useless.