Numbering Systems and Binary

1. Decimal (base-10)

The numbering system we use for most purposes is called the Decimal.  It consists of 10 numbers: 0123456789.

In the past, some civilizations used other numbering systems. For example, the Babylonians used the sexagesimal system, based on the number 60. This numbering system is why there are 60 minutes in an hour and 360 degrees (a multiple of 60) in a circle.
sexagesimal numbers

The Mayas used the vigesimal system, based on the number 20.
vigesimal numbers

2. Unary (base-1)

A base-1 numbering system was used by some people in ancient times before more advanced systems were developed. In a base-1 system, you simply put a tally mark (or a 1) for each item you are counting. For example, this ancient stick has 29 notches, possibly corresponding to the cycle of the moon:

ancient tally stick

Tally marks is another example of the unary numbering system.
tally marks

A numbering system that has elements of both Unary and Decimal is Roman - I, V, X, L, C, D, M.  The ancient Egyptian numbering system is similar.  The number below is 2,382,358.

Egyptian numbers

3. Binary (base-2)

The electronic circuitry within computers is composed of switches (latches) that have two states - on and off. Programmers represent the "on" state as 1 and the "off" state as 0. Since each switch has two states, the binary numbering system was created.

You may have noticed the 1 and 0 on power switches representing on and off.
power switch

Counting in binary can be tricky at first. The table below shows that you can count to 15 with a 4-digit binary number.

Counting in Binary
4-Digit Binary Decimal 4-Digit Binary Decimal
0000 0 1000 8
0001 1 1001 9
0010 2 1010 10
0011 3 1011 11
0100 4 1100 12
0101 5 1101 13
0110 6 1110 14
0111 7 1111 15

To convert a binary number to decimal, you need to see the value of each digit. Then you add those values for which the binary digit is a one.  The table below shows how to convert 10110101 to decimal.

Convert 10110101 to Decimal
Binary Number 1 0 1 1 0 1 0 1
Value of Each Digit 128 64 32 16 8 4 2 1

Add the values in which the binary is a one:  128 + 32 + 16 + 4 + 1 = 181

A bit is a single binary digit, which can be 1 or 0. A byte is 8 binary digits (8 bits), which allows you to count from 0 to 255. Data in computers is organized in bytes. The following table shows how the metric system is used to represent bytes.

Bytes and Metric System
Unit Size What it Can Store
bit 1 or 0 One bit can store answers to true/false or yes/no questions. E.g. Are you Covid-19 vaccinated?
byte 8 bits A byte can store a number from 0 - 255.  Each character of an ASCII document can be stored using one byte.
kilobyte (KB) 1,000 bytes A kilobyte can store a page of text.  Note: Sometimes a kilobyte is shown as 1,024 because it is a multiple of 2.
megabyte (MB) 1,000,000 (million) bytes A megabyte can store the text in a book.
gigabyte (GB) 1,000,000,000 (billion) bytes 6 GB can store an HD movie. 100 gigabytes can store a 4K movie.
terabyte (TB) 1,000,000,000,000 (trillion) bytes 10 TB can store the printed section of the Library of Congress.
petabyte (PB) 1015 (quadrillion) bytes Is is estimated that the human brain can store 2.5 PB of data.
exabyte (EB) 1018 (quintillion) bytes The size of data centers such as Google, Facebook, and AWS is measured in exabytes.
zettabyte(ZB) 1021 (hextillion) bytes The size of the entire World Wide Web is measured in zettabytes.
yottabyte (YB) 1018 (septillion) bytes A yottabye can store all of Yoda's knowledge ;-)

4. Doing Calculations with Binary

Example 1:  You have some video files that are 2 GB each.  How many of these files will fit on a 1 TB external hard drive?


Solution:  1 TB     1,000,000,000,000     1,000
           ----  =  -----------------  =  -----  = 
500 video files

           2 GB       2,000,000,000         2


Example 2:  How many 8 MB photos will fit on a phone with 24 GB free space?


Solution:  24 GB     24,000,000,000     24,000
           -----  =  --------------  =  ------  = 
3000 photos

           8 MB        8,000,000          8


5. Hexadecimal (base-16)

Hexadecimal is used by programmers to be a human-friendly representation of binary. It replaces 4 binary digits (bits) with one hex digit. Therefore, two hex digits are used to represent a byte. The table below shows 4 bits and the hex equivalent.

4-Digit Binary Dec Hex 4-Digit Binary Dec Hex
0000 0 0 1000 8 8
0001 1 1 1001 9 9
0010 2 2 1010 10 A
0011 3 3 1011 11 B
0100 4 4 1100 12 C
0101 5 5 1101 13 D
0110 6 6 1110 14 E
0111 7 7 1111 15 F

Often, a hexadecimal number is written with a 0x in front of it: 0xB means B hex, or 11 in decimal. OxFF means FF hex, or 255 in decimal.

6. ASCII Coding System

Since computers only store numbers, they need a coding system to represent text. One popular coding system used by Windows computers is ASCII. Each character of text is stored using one byte (8 bits) of memory. Spaces (ASCII 32) and punctuation marks also use one byte. Therefore, this sentence takes 40 bytes.


The extended ASCII characters (above 127) do not have keys on the keyboard. On Windows, these can be recreated by holding the Alt key and typing the ASCII number on the keypad (assuming you have a full keyboard). For example, hold the Alt key and type "171" on the keypad for the character ½.

7. Unicode Coding System

Unicode is another coding system that was created to add all the characters used in most of the world's written languages. This character set is now available on Windows and default on Mac. You can see the Unicode character set on this web site:

The Unicode character set uses 2 bytes giving 65536 different characters. The UTF-8 encoding specification allows each character to be one to four bytes. This allows it backwards compatible with ASCII. UTF-8 is a popular encoding for today's web pages.