programming-for-dummies

The History of Computer Programming 13
Registers
Book I
Chapter 1
Figure 1-1:
A processor
uses its
registers to
temporarily
store data.
Processor
Bus
RAM
Hard
Disk
Getting Started
Programming a
Computer
This command tells the processor to move (mov) the hexadecimal number
061h into the specific register named al. Other assembly language commands
might tell the processor to add (add) or subtract (sub) a value from
the number stored in a specific register.
When you use assembly language, you have to tell the processor what data
to store in which registers, how to manipulate the data in its registers, and
when to remove data out of its registers.
Sound tedious? It is. Although assembly language is far easier to understand
and write than machine language, it’s still too complicated to use for creating
really big computer programs, like word processors or video games.
In the old days, most programs were written in assembly language, but as
programs grew larger and more complicated, assembly language proved too
cumbersome to write, edit, and modify.
The biggest problem with assembly language is that you need to manipulate
the processor’s registers just to do the simplest tasks. If you wanted to add
two numbers together, you’d have to tell the processor to store a number
into a register, add a second number to the number in the register, and then
yank the result out of the register.
Forcing people to know how to manipulate the processor’s registers before they
can program a computer is like forcing people to know how their carburetor
works before they can drive a car. Ideally, you don’t want to tell the processor
how to manipulate data in its registers; you just want the processor to add two
numbers without worrying about specific registers. So to make computer programming
even easier, computer scientists have hidden the technical details
of manipulating registers by creating high-level languages.