A binary digit is called a bit. Usually expressed as 0 and 1 the two numbers of the binary numbering system.
A bit is the smallest unit of information a computer can use. A 16 bit computer would process a series of 16 bits,such as
0100111101011000 in one go, repeating the process thousands or millions of times per second.
Reading a series of bits is very difficult and to make this process easier they are often displayed in groups of 4 bits
0100 1111 0101 1000
This grouping is quite interesting in that a group of 4 bits can be replaced by a single hexadecimal digit
Two groups of 4 bits, i.e. 8 bits ( a byte) can be replaced by 2 hexadecimal digits,
and 4 hexadecimal digits are required to replace all 16 bits.
A group of 8 bits are in a byte. With 8 bits ( binary digits ), there exists 256 possible denary combinations.
If you remember that 1 byte can store one alphabetical letter, single digit, or a single character/symbol, such as #. Large numbers of bytes can be expressed by kilobyte and megabyte.
The value of a kilobyte is 1024. Worked out as 2^10. Normally Kilo refers to 1000 but in computing kilobyte is 1024.
Likewise, 1024Kb is referred to as a "Megabyte". Normally a Mega refers to a million. In computing 1 Mega byte is 1,048,576 bytes. Worked out as 2^20, or 1024*1024.
