Objectives:
To introduce the components of a modern desktop PC and examine the advances in processor
technologyidentify the components of a modern desktop PC
outline the role of the central processing unit (CPU) and printed circuit cards
identify the built-in connectors and input/output (I/O) slots on a typical motherboard
describe the function of the power supply unit
list the members of Intel's processor family
distinguish between the Pentium, Pentium II, Celeron, Pentium III, and Pentium
4 processorsidentify the other CPU manufacturers in the PC market
Lesson:
Many different desktop PC models are currently available on the market.
But the essential core of any PC consists of the following parts:
• keyboard
• monitor
• system unit
The system unit is the most complex and multifunctional of these three basic parts.
It acts as the engine of your PC, allowing its constituent parts to interact and work as a whole.
Within the system unit, every PC has a main printed circuit board that acts as its foundation.
This circuit card is known as the motherboard.
The motherboard can also be referred to as the main board, the systems board, or the planar board.
A central processing unit (CPU) is mounted on most modern motherboards.
The CPU plugs into a slot or socket fitting on the motherboard.
Several different slot and socket types have been developed for the PC market.
PGA370 socket and slot 1 (242-contact slot connector) are the most commonly used socket types.
The CPU is an integrated circuit chip that largely directs the activities of your PC.
Since it carries out a large share of the PC's work, data continually passes through the CPU.
It constantly receives instructions to be executed from other parts of the system.
Each instruction the CPU receives is a data processing order.
So the main work of a CPU involves calculations and data transport.
The CPU is located beneath or on the side of a large finned object.
This is called a heat sink and it's designed to absorb and dissipate heat generated by the CPU.
The heat sink is a vital aspect of any motherboard, as it prevents the CPU from overheating.
Typically, CPUs are built with two types of heat sink:
• passive
• active
A passive heat sink keeps the processor cool by absorbing heat through a finned metal cover.
An active heat sink, on the other hand, uses a powered fan to cool the processor down.
The CPU on many motherboards are surrounded by connectors that contain small circuit cards.
Each of these cards contains a series of integrated circuit chips.
In this motherboard from a sample desktop PC, one of the circuit cards holds the Level 2 (L2) cache.
Processors such as the Pentium III integrate the L2 cache within the SEC cartridge.
The cache memory in this system is built into a Cache On A Stick (COASt) module.
The COASt module is generally found in the Pentium and earlier processors.
The other circuit cards on this motherboard serve as its main memory subsystem.
This memory subsystem is known as random access memory (RAM).
Typically, two types of circuit card can be used to store RAM on your PC:
• single inline memory module (SIMM)
• dual inline memory module (DIMM)
The motherboard shown here happens to have three DIMMs installed.
The OR840 motherboard, for example, has four RIMM sockets.
Some other medium-sized circuit chips supply the main read-only memory (ROM) for the PC.
These are known as motherboard BIOS ROM chips.
They contain the programs that are used each time the PC boots.
Many modern motherboards store BIOS information in Flash RAM chips.
Flash RAM is a nonvolatile memory chip that can store information for long periods.
The data stored in a Flash RAM chip can be altered when necessary.
The other large chips on the motherboard contain what is known as the chipset or the glue logic.
For example, Intel's OR840 motherboard contains the Intel 840 chipset.
This chipset consists of three chips, the 82840 Memory Controller Hub, the 82801AA I/O Controller Hub, and the 82802AB Firmware Hub.
The chipset contains electronic circuits that are needed to transfer information across the motherboard.
The chipset circuits can be used in determining which location is being addressed in RAM or ROM.
They then cause the corresponding SIMM or DIMM chips to supply the information at that location.
The primary purpose of the motherboard is to link several functional parts of your PC.
It is the centerpiece of your system unit, therefore.
Any functional part of your PC that resides within the system unit must be attached to the motherboard by some means.
For this reason, it has several built-in connectors and input/output (I/O) slots.
The I/O slots are long rectangular connectors, located in the top left-hand section of this motherboard.
They are designed to hold plug-in cards hosting a wide variety of functional parts.
For example, you could attach a graphics adapter to the motherboard by plugging it into one of these slots.
Some other common plug-in cards include a network interface card (NIC), an internal modem, and a SCSI host adapter.
The true benefit of I/O slots is that they make your system unit fully extensible.
You can upgrade the motherboard when necessary and gradually extend its functionality over time.
On this motherboard, the bottom right-hand section is reserved for connectors.
Cables for floppy disk drives and any peripheral devices you have mounted inside the system unit can be attached to these connectors.
The clock battery is located towards the back of the motherboard here.
This battery powers both the real-time clock and the system clock.
It's connected to the motherboard, but remains independent of the main power supply.
The real-time clock maintains the correct date and time, even when your PC is turned off.
The system clock dictates the sequence of execution for most actions within the PC when its power is on.
The system clock operates a regular pattern of alternating high and low voltages.
System clock speed is measured in Megahertz (MHz).
1 MHz is a signal that alternates between high and low values 1 million times a second.
So a 133 MHz PC clock generates alternating values 133 million times each second.
Each set of values in an alternating sequence is called a clock cycle.
The clock signal directs many important system operations.
It informs specific circuits when to start transmitting data.
It also tells other circuits when the data from that clock signal should arrive.
The earliest PC had only one clock - its signal was sent to the CPU, memory, and all the I/O devices.
A modern PC has many different clock signals that are sent to different areas of the machine.
A collection of circuit chips and connectors are built into the back of the motherboard.
These connectors are designed to sit flush against the back panel of the PC.
The printer, mouse, and keyboard all attach to these connectors.
The circuits on the motherboard implement the serial, parallel, and USB ports.
PS/2 keyboard and PS/2 mouse ports are also attached to the motherboard shown here.
To connect peripheral devices to a computer, you can use
• a USB (universal serial bus)
• an IEEE 1394 serial bus
• Infrared
USB is a low-cost connection for multiple simultaneous input devices such as printers,
joysticks, keyboards, mice, scanners, modems, and removable drives.Using USB, you can connect peripherals in a daisy-chain, tree, or star architecture.
You do not need to shut down and then reboot to add or remove devices using USB.
You can also connect attachments in any order.
For example, you can plug a keyboard and a printer into a computer, connect a mouse and a joystick to the keyboard, and then attach a scanner through the printer.
USB's features include
• a data transmission rate of 12 Mbps
• support for 127 devices
• hot plug-and-play capability
• both isochronous (real-time) andasynchronous data transfers
• cables up to 5 meters long
• built-in power supply distributionfor low-power devices
USB 2.0 increases the speed of the connection between the peripheral and the computer from 12 Mbps on USB 1.1 to 480 Mbps on USB 2.0.
USB 2.0 is fully forward and backward compatible with current USB systems and peripherals.
An IEEE 1394 (Firewire) serial bus enables simple, low-cost, high bandwidth, isochronous data interfacing between computers, peripherals, and electronic products such as PCs, TVs, camcorders, and digital cameras.
You can connect 63 devices on an IEEE 1394 bus using a daisy-chain and a tree-structure topology.
The IEEE 1394b standard increases the speed of data transmission from 400 Mbps to 3200 Mbps.
IEEE 1394b supports CAT 5 UTP, plastic and glass optical fiber transmission media.
Infrared is ideal for high-speed, short-range, line-of-sight, point-to-point cordless data transfer.
Infrared is suitable for handheld data collection devices, digital cameras, notebooks, and palm PCs.
With Infrared, continuous operation can range up to 2 meters.
Data transmission rates vary from 9.6 Kbps to 4 Mbps.
Many small, additional connectors and a few jumper blocks are dotted around the typical motherboard.
These connectors are attached to cables that operate the front panel's lights and switches.
The front panel of most PCs includes a display light for all system unit disk drives and the power supply.
There is a certain degree of flexibility built into modern motherboards by design.
You can change certain configurations of a motherboard by placing a jumper plug across certain pins on the jumper block.
You should check the manual that shipped with your motherboard to determine what certain jumper or switch positions do.
The power supply unit is one of the most fundamentally important pieces attached to the motherboard.
This unit converts raw energy from alternating current (AC) to direct current (DC).
Your PC will store some of the incoming energy in reserve, so that it can survive brief interruptions in the electrical input.
The power supply unit for this sample PC has several output connectors.
The largest of these connectors is attached to the motherboard.
The other connectors on the unit are used to power system disk drives.
Most modern desktop PCs can support at least one floppy disk drive, and up to four
of the following drives:• IDE
• EIDE
• CD-ROM
• tape
• zip
The power supply connectors can carry four different voltage levels:
• +12 volts
• +5 volts
• -5 volts
• -12 volts
Several chips on the motherboard need different voltage levels to perform correctly.
But as CPU speeds have increased, manufacturers have started lowering voltages to the motherboard.
This measure is intended to prevent the CPU and other associated components from overheating.
One of the recent advances in CPU technologies is the use of increasingly thinner wires inside the chip.
With thinner wires, the CPU can operate at a lower voltage.
This results in a smaller CPU operating at higher speeds, yet generating less heat.
The power supply unit also has to monitor the quality of DC voltages it supplies
to the rest of the PC.If this voltage drops below an acceptable level, the power supply unit lowers the voltage to the motherboard.
In response, the computer simply resets itself and begins computing again when the voltage returns to a suitable level.
It's possible to purchase special backup power supplies that can keep your PC working during a power cut.
Such a system is called an uninterruptable power supply (UPS).
As the UPS works off a battery and battery charger, it could keep your PC working for up to an hour after the initial power cut.
Most modern power supply units are in switch mode, and they should never be opened unless you are familiar with their internal workings.
You could receive a severe electrical shock, as the unit typically switches a very high voltage at a very high frequency.
All the electric energy that the power supply unit channels into the motherboard and the disk drives is ultimately converted into heat.
If the CPU or any other component on your motherboard becomes too hot, it will either blow or burn out prematurely.
To prevent this, the PC power supply unit has an internal fan that moves the heat generated by normal computing away from the motherboard.
The fan in your PC should be mounted on roller bearings, to minimize noise.
The power supply's fan is often not enough to ensure that your system doesn't overheat.
Your PC could be loaded with several power-hungry plug-in cards and a CPU running at 1000 MHz or more.
In such circumstances, you'll need both a heat sink and a fan to protect your PC from overheating.
The bigger the fan and heat sink, the better your PC will function.
The CPU will operate more reliably and it will have a longer life span.