programming-for-dummies

The History of Computer Programming 11
In the old days, computers filled entire rooms and cost millions of dollars.
Today, computers have shrunk so far in size that they’re essentially nothing
more than a little silicon wafer, about the size of a potato chip. These silicon
wafers are called the central processing unit (CPU), a microprocessor, or just
a processor.
A processor is essentially an entire computer. To tell the processor what to
do, you have to give it instructions written in machine language — a language
that the processor can understand.
Book I
Chapter 1
Getting Started
Programming a
Computer
To make faster computers, engineers smash two or more processors
together and make them work as a team. So instead of having a single
processor in your computer, the latest computers have two, four, six, or
more processors working side by side.
Talking to a processor in machine language
To understand how machine language works, you have to understand how
processors work. Basically, a processor consists of nothing more than millions
of tiny switches that can turn on or off. By turning certain switches on
or off, you can make the processor do something useful.
Instead of physically turning switches on or off, machine language lets you
turn a processor’s switches on or off by using two numbers: 1 (one) and 0
(zero) where the number 1 can mean “turn a switch on” and the number 0
can mean “turn a switch off.” So a typical machine language instruction
might look like this:
1011 0000 0110 0001
If the preceding instruction doesn’t make any sense, don’t worry. The point
is that machine language is a just way to tell a processor what to do.
Using 1’s and 0’s is binary arithmetic. Because binary arithmetic can be so
hard to read, programmers also represent binary numbers in hexadecimal.
Where binary arithmetic uses only two numbers, hexadecimal uses sixteen
numbers (0–9 and A–F). So the binary number 1011 0000 0110 0001 could be
represented as the hexadecimal number: B061.
Machine language is considered the native language of CPUs, but almost no
one writes a program in machine language because it’s so tedious and confusing.
Mistype a single 1 or 0 and you can accidentally give the wrong instruction
to the CPU. Because writing instructions in machine language can be so
difficult and error-prone, computer scientists have created a somewhat simpler
language — assembly language.