Bits, bytes and binary

A bit is the smallest piece of information possible. That is, it is either 1 or 0, On or Off, True or False. Why is this important? Because computers only work with On and Off. They use transistors as a gate that is either open or closed like this –

 Gate1

The three lines at the bottom are earth or 0 volts

When there is no input signal, the gate is closed, the transistor blocks any flow of current in the direction of the arrow, so the output signal is at the same voltage as the power source. This is a 1.

Closed

When the input signal goes positive, the gate opens, and the transistor effectively shorts the circuit, dropping the output signal to earth or 0 volts. This is a 0.

 Open

Not very useful, you might think, but all computer processors use this very simple circuit to generate bytes and drive your computer logic.

Here’s a typical byte – 01000111. It requires 8 transistors, four of which are switched on and four off. It is sufficient to describe one character (actually, the character G) in computer language, or binary code. It is the binary number 71 (64 + 4 + 2 + 1)

binaryG

Can you imagine how many transistors it takes to build a modern desktop computer? When I was a student, transistors had only been in commercial production for 10 years and looked like this –

Transistor

About 6mm diameter and 7mm deep. Now we have microprocessors chips –

Chip

A microprocessor consists of about 10 billion transistors. That’s 10 000 000 000! That’s progress for you. In fact, your smartphone has more computing power than NASA had when man first landed on the moon.

 

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