Chapter 1 Introduction to a Typical PC 23
3. After the fi rmware checks the computer
components, the operating system takes
control. There are many different types of
operating systems, but for our example,
Windows software will be used.
4. The CPU now waits for activity to be
generated by the mouse, keyboard, modem,
or other input device. The CPU constantly
checks if a key is pressed or the mouse is
moved or clicked. The CPU checks these
items thousands of times per second.
5. The mouse pointer is moved to an icon, and
the mouse is clicked to activate a desired
program—a word-processing program in this
example. The software represented by the
icon is activated. It now shares control of the
computer with the CPU.
6. Some typing is done, and then the save
command is issued by clicking a save-the-
data icon in the word-processing program.
The program now attempts to save to the
Documents
folder. When the word-processing
program saves, the operating system takes
over in conjunction with the fi rmware. The
operating system interprets the command
issued from the word-processing program
and translates it to a set of instructions that
the fi rmware can interpret.
7. The fi rmware, in turn, translates the
instructions to the storage media which is
most commonly the hard drive. It activates
the hard drive motor and actuator arm,
moving it to the next available sector on
the disk. Information about available disk
space is kept in a table. The operating system
and fi rmware work together until all data
is transferred and recorded on the storage
media.
8. Control is then returned to the word-
processing program, so long as an error has
not occurred. Possible errors are disk full or
unable to read disk.
The cooperation between the word-
processing program, operating system, and
firmware goes unnoticed by the user.
Integrated Circuits
The term chip is often used in the computer
industry. A chip is actually the final product of
the manufacturing of an integrated circuit. An
integrated circuit (IC) is a collection of transistors,
resistors, and other electronic components reduced
to an unbelievable small size. In fact, over six
million transistors manufactured as an integrated
circuit can fit into an area the size of a dime. Chips
are commonly found on circuit boards. They are
the black, square and rectangular devices.
Manufacturing an Integrated
Circuit
The manufacturing process that creates an IC
consists of many hundreds of steps in a process
covering a period of several months. The first step
in the manufacture of a chip is the design of the
circuit. The circuit is drawn on a very large scale.
When the design is completed and all drawings
are finished, the manufacturing process is ready
to begin. First, the drawings are photographed.
The negative of the drawing’s photograph is used
as a template in the manufacturing process. See
Figure 1-34.
An ingot of pure silicon is made and then
sliced into thin wafers to serve as the base of the
IC. Silicon is the same as most common beach
sand, but it is extremely pure. The material cannot
contain any impurities that might cause adverse
effects in the manufacturing of the IC. A series of
layers are produced over the surface of the silicon
wafer using a process called photolithography.
Photolithography is described in the following
sequence of events. First, a heat process vaporizes
silicon dioxide. Then, various other chemicals are
used to form many extremely thin layers over the
surface of the wafer. After each layer is formed, a
coating of a chemical called photoresist is laid over
the entire surface of the wafer. The photoresist
reacts when exposed to ultraviolet light.
The negative from the photograph of the
circuit is used as a stencil. The negative is called
the photomask. When ultraviolet light shines
through the mask, it causes the photoresist to
leave a pattern of soft and hard surfaces in the
exact pattern of the designed circuit. The soft
photoresist is then washed away leaving an etched