Computer Systems Nat 4/5 Computing Science Lesson 1: Binary

Section Key Words Section Key Terms

Lesson Aims  By the end of this lesson:  You will be able to: Describe what an integer is Represent positive integers in binary using up to 8 Bits State three advantages of the binary number system

The Decimal & Binary Systems  We use the decimal(denary) or base 10 system  This means we have 10 digits : 0-9  Computers use the binary or base 2 system  There are only two digits: 0 and 1  Each figure is known as a bit  Bi nary digi t Nat 4/5 Off and On Because of our ten fingers?

Decimal Numbers  Lets look at how a decimal number is made up: 173  Technically this is: Nat 4/5 HundredsTensUnits HundredsTensUnits 173

Binary Numbers  Lets look at how the same number is stored in binary: Nat 4/  This number is constructed as shown above.  These values come from:

How to convert into Binary  Let’s look at the same example:  173/2 = 86 r 1  86/2 = 43 r 0  43/2 = 21 r 1  21/2 = 10 r 1  10/2 = 5 r 0  5/2 = 2 r 1  2/2 = 1r 0  1/2 = 0 r 1  Binary Number = Nat 4/5 This is our binary number Our binary number is: Read the binary number from bottom up.

How to convert into Binary  Using the number 173 earlier. The aim is to subtract the values from the number until we are left with 0.  Can we subtract 128 from 173?  Yes – So we add a 1 to our number  Can we subtract 64 from 45?  No so we add a 0  Can we subtract 32 from 45?  Yes so we add a 1  Can we subtract 16 from 13?  No so we add a 0  Can we subtract 8 from 13?  Yes so we add a 1  Can we subtract 4 from 5?  Yes so we add a 1  Can we subtract 2 from 1?  No so we add a 0  Can we subtract 1 from 1?  Yes so we add a 1 Nat 4/5 Read the binary number from top down Our binary number is:

How to convert from Binary 1. Create your table with the values in the top 2. Insert your binary value into the table 3. Add the place values that have a binary 1 in them: = 102 Nat 4/

Advantages of the Binary system There are less rules of arithmetic, this makes it easier to program. 0’s and 1’s are easier to represent digitally in computer systems. Any drop in voltage does not affect the data. Nat 4/5

Advantages of Binary: 1.There are less rules of arithmetic. 2.0’s and 1’s are easier to represent. 3.Any drop in voltage doesn’t effect data. Summary  Binary only has two values– 0 & 1  A single 0 or 1 is known as a bit  Binary Digit  The place values in binary start on the right at 1 and double every time going to the left. Nat 4/5