Inside the system unit

The system unit is a magical box that you’ll probably never need to open. But someday, you’ll get curious about what’s inside.
Inside a Computers Simplified

 Inside a Computer -- Part of the Computer Motherboard

How to peek

Here’s how to peek inside a desktop computer’s system unit.

· Make sure the computer’s turned off.

·  Remove the screws from the 4 corners of the system unit’s back wall. Notice how big those screws are. Remove any other screws of that size from the back wall’s edges.

·    Then remove the system unit’s cover:

·    If the unit’s a tower, pull the cover back slightly, then lift it.

·    If the unit’s a desktop, slide the cover forward — or if it refuses, try sliding the cover back — then lift it slightly.

·    If the cover doesn’t quite come off, jiggle it slightly, and also double-check whether you’ve removed all the screws holding it in place.

·    Finally, peek into the system unit and admire the goodies within! To be safe, avoid touching them.

Circuit boards

Inside the system unit, you see several green plastic boards, called circuit boards (because they have electric circuits on them). On each circuit board, you see many black rectangular objects, called chips: each chip contains a miniature electronic circuit inside!

Motherboard (Mobo)

The motherboard is a large electronic board that is used to connect the power supply to various other electronic parts, and to hold these parts in place on the computer.

The motherboard contains the buses, or electrical pathways found in a computer. Buses allow data to travel among the various components.

The motherboard accommodates CPU, RAM, expansion slots, heat sink/fan assembly, BIOS chip, chip set, sockets, internal and external connectors, various ports, and the embedded wires.

Also found on the motherboard is the BIOS (Basic Input and Output System) chip that is responsible for some fundamental operations of the computer, such as linking hardware and software.

The motherboard also contains a small battery (that looks like a watch battery) and the chips that work with it to store the system time and some other computer settings.

The layout or form factor determines what sort of casing the motherboard needs and provides a maximum expansion slot limit. Making some parts removable enables one to upgrade or expand system.

Upgrading means changing to newer, usually more powerful or sophisticated versions such as more memory chips while Expansion is a way of increasing a computer's capabilities by adding hardware to perform tasks that are beyond the scope of the basic unit.

CPU

On the mobo, the biggest chip is the one that does most of the thinking. It may be likened to the Central Nervous System of an animal.  That chip is called the central processing unit (CPU). It’s also called the microprocessor.

A standard computer uses a brand of microprocessor called a Pentium, manufactured by an intelligent California company called Intel.

Yes, in a microcomputer, most of the thinking is done by a single chip, called the microprocessor.

In older, bigger computers, the thinking is done by a gigantic collection of chips working together, instead of a single microprocessor chip. That collection is called the processor. The term microprocessor was invented by folks amazed that a processor could be made small enough to fit on a single chip.

All other devices such as the input, output and storage devices are connected to the CPU and are called peripherals. 

An instruction is made up of operations that specify the function to be performed and operands that represent the data to be manipulated.  For example if the instruction is to perform the operation of multiplying two numbers, there are two things that need to be taken into consideration that is:

  What the two numbers are, and

 

The job of the central processor is to retrieve instructions and data from memory and to perform each operation.

Processor models were initially named in numbers for example 80286 or simply 286.  Some examples of the processors are 386dx, 386sx, 486DX2, 486DX4, 586 or Pentium 1, Pentium II, Pentium III, Pentium IV. 

We now also have the AMD K-6 Processors.  The type of processor determines the speed and efficiency of the computer.  Generally the higher the processor model number, the faster the processor.

Processor Speed

The speed of the processor is measured in Megahertz (MHz) which means million cycles or instructions every second.  The speed of the computer is actually given by the Clock of the computer which sends timed electrical signals every second and provides the processor’s heartbeat.

A processor is made up of two functional units and a set of workspaces, that is Control Unit, Arithmetic Logic Unit (ALU) and Registers respectively.

The Control Unit

The Control Unit is responsible for supervising the operation of the processor.  It does the fetch and execute job, that is retrieving instructions from memory and executing them accordingly.

The control unit is driven by a clock pulse.  The rate of the clock directly affects the processor speed and it is measured in Megahertz (MHz).

The Arithmetic Logic Unit (ALU)

As the name states this is responsible for all mathematical operations. 

It receives data from the Control Unit and performs either Arithmetic operations (add, subtract, multiply and divide) or Logic operations (making a comparison and take an action based on the result) for example If A=2 End, Else Begin. 

This example shows that if A is equal to 2 the program should end and if not equal it should start the operation again.

What Are Registers?

Registers are storage locations inside the processor.  Registers in the control unit are used to keep track of the overall status of the running program. 

 Control unit registers keep current instructions and the operands of the instruction.  There are also ALU registers that store data items that are to be added, subtracted, multiplied, divided or compared.

Expansion cards

Besides the motherboard, the system unit contains smaller circuit boards (called expansion cards) that snap into slots in the motherboard.

The most important expansion card is the video card. It manages the monitor. It includes the video port, which attaches to the cable that comes from the monitor.

Another expansion card is the sound card. It manages the stereo speakers and microphone and attaches to the cables that comes from them.

Another expansion card is the modem (pronounced “mode em”). It manages phone signals and attaches to cables that come from the phone and the phone jack.

If your computer is part of a local-area network, your computer includes a network interface card (NIC), which attaches to the network cable that comes from the network’s other computers.

The keyboard does not have its own expansion card. Instead, the keyboard’s cable plugs directly into the motherboard.

Computer hardware Exercise

Memory

The three most popular kinds of memory are ROM chips, RAM chips, and disks.

ROM chips remember info permanently. Even if you turn off the computer’s power, ROM chips continue to remember what they’ve been told. The most important ROM chips are on the motherboard.

RAM chips remember info temporarily. They’re electronic scratchpads that the CPU uses to store temporary reminders. For example, they remember what problem the computer’s working on at the moment. They get erased when you switch to a different computer problem or turn the computer off.

In an old computer, most RAM chips are on the motherboard, where the RAM chips are arranged in rows, 8 or 9 RAM chips per row. In a new computer, the RAM chips are instead on tiny expansion cards, which snap into tiny slots on the motherboard: each tiny RAM cards is called a single in-line memory module (SIMM) and holds 3, 8, or 9 RAM chips.

Disks work slower than ROM chips and RAM chips but can hold more info. Like ROM chips, disks can remember info permanently: unplugging the computer does not erase the disks. To use a disk, you must put it into a disk drive, which reads what’s on the disk.

In a traditional computer, the system unit includes 3 disk drives, to handle 3 kinds of disks:

A CD-ROM disk looks like a Compact Disk (CD) that music comes on, but a CD-ROM disk contain computer data instead of just music.

A floppy disk is made of flimsy material but comes encased is a sturdy square jacket, which is typically 3½ inches on each side (though older disks come in 5¼-inch jackets instead). You can insert the floppy disk (including its jacket)  into the floppy-disk drive. You can also remove the floppy disk (including its jacket) from the drive.

The typical hard disk is made of hard material, hides in the hard-disk drive permanently, and never comes out, so you never see it.

Each of those three types has its own advantages:

CD-ROM and floppy disks can be removed from their drives.

The typical hard disk cannot.

You can edit info if it’s on a hard disk or floppy disk,

but not if it’s on a typical CD-ROM disk.

The typical hard disk can hold lots of info.

The typical CD-ROM disk holds less.

A floppy disk holds even less.

The newest computers can also handle DVD disks (which hold movies and computer data) but don’t bother handling floppy disks.

Power supply

The power cord comes from your office’s wall and goes into the back of the system unit. Look inside the system unit, at the back wall, where the power cord goes in.

There you see, inside the system unit, a big metal box, called the power supply.

Hands on Exercise for you. Kindly fit in all the inside parts of a desktop computer. Click on the image below: