by eturo
In this article, you will learn about PC
computer cases and the various types that are available. You will learn about
the different parts of a computer case and the purpose of each, and you will
learn what type of motherboard is compatible with the type of computer case.
Next, you will learn about power
supplies and computer cases and the role of power supply in a PC, you will
learn how to remove and replace a power supply, as well as how to select a
replacement model if your power supply should fail. You will also learn about
the different kinds of power connections that come with a power supply.
Finally, you will learn why it is
important to keep the inside of your computer case cool.
A.
CASE FORM and
FUNCTION
Computer Case
¾
is
made up of metal (or sometimes plastic), it’s the box that houses all the
components and devices that make up a computer
External Size
One of the first issues to consider
when selecting a case is the external dimensions. The case you choose depends
on several interrelated factors:
o
Do
you plan to upgrade the system at a later date?
o
Who
will be using the system?
o
What
will be the final location on the system (for example, on top or beneath a
desk)?
Different
Types of Computer Cases
1. Full-Tower
Cases
¾
it
is likely to be the largest PC case (except for the massive server-style cases)
¾
at
least 2 feet tall that provides a maximum amount of interior space for a
variety of drives and expansion cards
¾
should
have at least four externally accessible drive bays for CD-ROM, CD-RW, and DVD-ROM
drives as well as two external floppy disk drive bays
¾ most full-tower cases have internal
space for at least three, and sometimes as many as five hard drives
2.
Mid-Tower Cases
¾
it
is very common because of the flexible design
¾
it
is usually stands about 20 inches high and has an average of three external
drive bays and one external floppy drive bay
¾
has
fewer internal drive bays, but it can sometimes hold a pair of hard drives
3. Mini-Tower
Cases
¾
usually
smaller and a little wider that a mid-tower case
¾
provide
the least amount of interior cooling so they are not the best choice
¾
have
only two external drive bays and one internal bay
4. Desktop
Cases
¾
it
lies flat on its larger side means that they are designed to sit on a desk with
a monitor resting on top of it
¾
usually
does not provide much capacity for expansion
5. Server
Cases
¾
usually
quite large with plenty of bays and expansion slots
¾
rather
than favoring in rectangular design like tower case, they tend to be in square
6.
Rack-Mount Cases
¾ used
exclusively by businesses that need a space-efficient way to organize large
numbers of servers
¾
they
are sized by unit (a single unit is 1.75 inches high)
¾
described
according to the number of units (U’s – multiple of 1.75 inches) high they are
§
example:
a 3U case is 5.25 inches high (3 x 1.7 inches)
¾
Note:
Even though rack-mount cases have different heights, they are always 19 inches
wide to fit into standard equipment racks.
Drive Bays
¾
these
are special areas to hold storage drives found in all cases
Two types of drive bays:
§
external
bays – have openings that enable to be accessed from outside the case
¾
used
to hold components like floppy disk drives and CD-ROM drives
§
internal
bays – used to hold internal components like hard drives
¾
comes
with two widths: 3 ½ inches and 5 ¼ inches
Ø
3
½ - Inch Bays
o
normally
used for a floppy drive and for hard drives
Ø
5
¼ - Inch Bays
o
back
to the days when computers used only 5 ¼ - inch floppy disk drives
o
this
bays remain because it is used for optical media like CD-ROMs and DVD-ROMs
drives
¾
rails (drive rails) – is used to mount new devices in
drive bays
Back Plates
¾
a
metal plate punched at the back of a case with a specific set of holes designed
to allow various external connectors on the motherboard to punch through the
back of the case
Nice to Know!
One way of
determining whether a computer case will accept the type of motherboard you
plan to use is by looking at the back plate to see if the holes match your
motherboard’s external connectors.
Screws and Stand-offs
Types of screws:
§
fine-threaded
screws – are used almost exclusively for mounting CD media drives
§
coarse-threaded
screws – used to mount all other devices which usually come in large and small
size
•
larger
mounting screws have a hexagonal head with notches for a Phillips-head
screwdriver
•
smaller
mounting screws usually have either hexagonal or rounded heads
§
stand-off
screws – are designed to be attached to the inside walls of the case and fit
through holes in the motherboard
Case Form Factors
¾
the
type of case you buy depends on the type of motherboard you want to use
¾
when
building a computer, you should first choose the motherboard and then a case of
the corresponding form factor to go along with it
Four Main Form Factors for Cases and
Motherboards:
§
AT
¾
this
form factor used in older computers
¾
not
many cases are built for AT motherboards anymore because they are now obsolete
§
ATX
¾
these
are the most common form factor found in modern PCs
¾
it
can fit into any tower case, as well as into desktop and some larger rack-mount
cases and even in server cases
§
microATX
¾
these
case form factors are available ranging from mid-tower and mini-tower cases to
desktop cases
¾
designed
specifically to accommodate businesses use as a file server
¾
mid-tower
and mini-tower cases can accept both ATX and microATX
§
FlexATX
¾
the
smallest ATX form factor
¾
FlexATX
motherboard form factor was created specifically for 1U rack-mount cases
Power Supply – it act as a step-down transformer;
means that it converts high-voltage (115 volts in the U.S.,240 volts in the R.P.)
Alternating Current (AC) into low-voltage (12, 5, and 3.3 volts) Direct Current
(DC)
§
12-
volts current to power motors on devices like hard drives and CD-ROM drives
§
5-volt
and 3.3 volt current to support onboard electronics
Two
types of Power Supply:
•
AT Power Supply – it is the older style from the early days of the PC
•
ATX Power Supply – use for modern PCs, which is
matched to an ATX (ATX, microATX, or FlexATX) form factor motherboard and case
Features
of Power Supplies:
•
Power connection – power supplies must plug into a
power outlet
•
Motherboard power – these must be some connection to
provide power to the motherboard
•
Peripherals connections – there must be connectors to provide
power to internal devices
•
Fan – a critical component both cools the
inside of the power supply and provides
cooling airflow throughout the case
Wattage
¾
power
supplies are rated in watts
§
it
is the standard measurement unit of power, or energy/time
¾
several
problems occur if there’s insufficient wattage:
§
The
PC will fail to complete the Power-On-Self-Test (POST).
§
The
PC will complete the POST but will fail to load the Operating System (OS).
§
The
PC will complete the POST and load the Operating System, but it will reboot
simultaneously once a load is applied to the CPU or other hardware.
¾
at
least (minimum) 400-watts should a
power supply needed to bootup for modern PCs
Connectors
¾
there
are many different types of power connectors that you might encounter,
depending on the type of power supply in a computer
¾
among
these connectors are as follows:
o P8/P9
Power Connectors
§
a
power connector used by AT power supply that plugs into an AT motherboard
§
it
must be plugged in with the black wires next to each other
§
NOTE: Keep the black wires together!
Failure to do so will result in a fried motherboard.
o P1
Power Connectors
§
a
power connector used by modern ATX power supply that plugs into an ATX
motherboard
§ it includes a 3.3-volt wire long with
the standard 5V (motherboard) and 12V (e.g. CD-ROM drives)
o
Molex Connectors
§
it
is the most common type of power connection for devices that need 5 or 12 volts
§
it
has notches called “chamfers” , that are supposed to guide for its installation
o Mini
Connectors
§
it
is the standard connector for 3 ½ floppy drives
§
referred
as the floppy power connectors
o P4
Power Connector
§
a
12-volt, 4 pin DC connector designed based on Pentium processors used by an
ATX12V power supply to supply extra power to the motherboard
¾
a
good-sized server can require a power supply of 550 watts or more
Power Switches
¾
Every
PC turns on and off by means of a power switch
§
AT
power switches simply turn the system on or off
§
on
ATX power supplies, the power switch interacts with the power supply using a
feature called soft power
o
AT Power Switches
§
has
two and interchangeable types: rocker
and plunger
§
each
has four tab connectors that attach to four color-coded wires leading from the
power supply
§
both
types of AT power switch can handle 120 volts of power
o
AT Power and Power Management
§
most
modern computer systems have the ability to shutdown hardware not currently
needed by the system
§
hibernate mode (sometimes called sleep mode)– the ability to shutdown or goes into frozen all the devices,
including the CPU temporary
§
AT
systems do not support power management wee, but that does not mean they do not
support power management at all
o
ATX Soft Power
§
soft power – it works by keeping the system
from ever completely shutting off
§
an
ATX power supply never turns off as
long as an ATX system is receiving AC power from the wall socket, the ATX power
supply puts a 5-volt charge on the motherboard
§
many
ATX power supplies provide a real on/off
switch on the back of the system
Power Supply Fans
¾
it
provides the basic cooling for the PC
¾
it
does not only cools the voltage regulator circuits within the power supply; it
also provides a constant flow of outside air throughout the interior of the
computer case
¾
a
dead power supply fan can rapidly cause tremendous problems, even equipment
failure
C.
COOLING
¾
Cooling
is a vital consideration when building a computer. Because computers, being
electrical devices, generate heat as the operate, and too much heat can
seriously damage a computer’s internal components
¾
the
CPU generates the greatest amount of heat
Power Supply Fan
¾
every
power supply has a built-in fan to help
keep its components cool
§
cools
the power supply itself
§
helps
circulates air inside the case to cool the rest of the components
Heat Sinks and Fans
¾
CPU heat sink – a pile of molten silicon device which
is snaps directly on top of a CPU and draws heat from the core of the processor
up copper or aluminum vanes to be dissipated by the fan
¾
CPU fan – a fan that sits on top of a heat
sink that also plays a role in circulating the air inside the computer case
§
You
can theoretically keep your computer case cooler by putting a larger fan on the
CPU heat sink, but larger fans are often very noisy.
§
Without
proper airflow through a case, a heat sink fan may simply recycle the same
heated air over and over that could possibly raise the temperature of the CPU
rather than lowering it.
Case Fans
¾
these
are large, square fans that snap into special brackets on the case, providing
extra cooling for key components
¾
the
biggest issue related to case fans is where to plug them in
§
most
case fans come with standard Molex connectors
§
other
case fans come with special three-pronged power connectors that need to connect
to the motherboard
o
get
adapters to plug three-pronged power connectors into Molex; or
o
Molex
connectors into three-pronged connectors
Airflow
¾
a
closed case enables the fans to create airflow
¾
the
airflow substantially cools off interior components
¾
when
the side of the case is open, you ruin the airflow of the system, and you lose
a lot of cooling efficiency
¾
another
important part of maintaining proper airflow inside the case is ensuring that
all empty expansion bays are covered by slot
coversof the cases
