Download System Unit And The Processor

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The main circuit board of a microcomputer. The motherboard contains the
connectors for attaching additional boards. Typically, the motherboard
contains the CPU, BIOS, memory, mass storage interfaces, serial and
parallel ports, expansion slots, and all the controllers required to control
standard peripheral devices, such as the display screen, keyboard, and disk
drive. Collectively, all these chips that reside on the motherboard are known
as the motherboard's chipset.
On most PCs, it is possible to add memory chips directly to the
motherboard. You may also be able to upgrade to a faster PC by replacing
the CPU chip. To add additional core features, you may need to replace the
motherboard entirely.
The function of the motherboard lies within the name of the part itself: it's a
board (specifically, a circuit board) and it's the mother of everything in your
computer - all connections have to go through it. Video hardware is plugged
into it. The DVD drive is plugged into it. The scanner plugged into your USB
hub? That hub is plugged into the motherboard.
During the late 1980s and 1990s, it became economical to
move an increasing number of peripheral functions onto the
In the late 1980s, motherboards began to include single ICs
(called Super I/O chips) capable of supporting a set of lowspeed peripherals: keyboard, mouse, floppy disk drive, serial
ports, and parallel ports. By the late 1990s, many personal
computer motherboards supported a full range of audio,
video, storage, and networking functions without the need for
any expansion cards at all; higher-end systems for 3D
gaming and computer graphics typically retained only the
graphics card as a separate component.
A control unit is a key component in all computer systems.
It works with the central processing unit to instruct,
maintain and control the flow of information. Without a
control unit, a computer could not follow directions and
might not function properly. This is especially true of
electronic devices that require timing or logical thinking
when in operation.
A CPU is the control unit in most electronics. A control unit
is often referred to as a method to direct traffic--traffic in
this sense represents the flow of information and circuits.
This includes timing, logical operations and synchronizing
information. Mainframes, traffic lights and monitoring
security cameras are equipped with control units
The control unit coordinates the components of a
computer system. It fetches the code of all of the
instructions in the program. It directs the operation of the
other units by providing timing and control signals. All
computer resources are managed by the CU. It directs the
flow of data between the Central Processing Unit (CPU)
and the other devices.
The control unit was historically defined as one distinct
part of the 1946 reference model of Von Neumann
architecture. In modern computer designs, the control unit
is typically an internal part of the CPU with its overall role
and operation unchanged.
Comparison of Personal Computer
• The part of a computer that interprets and carries out instructions
provided by the software. It tests and manipulates data, and transfers
information to and from other components, such as the working memory,
disk drive, monitor, and keyboard. The central processing units of personal
computers are generally implemented on a single chip, called a
• the part of a computer (a microprocessor chip) that does most of the data
processing; "the CPU and the memory form the central part of a computer
to which the peripherals are attached"
Some more stuff about Comparison of
Personal Computer Processors
• Intel approaches the situation differently by only sharing level 2 cache,
which works in its favor since there is a pool of information for each
processor to pull from. This means information gets to the processor and
back to the Cisco compatible GLC-T module faster than in an AMD
processor. Additionally, Intel has been integrating more controllers in their
processor to make the computer a simpler device, and even though high
end Cisco compatible SFP modules are not integrated yet, technology is
headed that way.
• Even though most applications thrive when using more cores to process,
there are still simple tasks that have more of a benefit from just using a
single core.
Parallel Processing
 In general, parallel processing means that at least two microprocessors
handle parts of an overall task. The concept is pretty simple: A
computer scientist divides a complex problem into component parts
using special software specifically designed for the task. He or she then
assigns each component part to a dedicated processor. Each processor
solves its part of the overall computational problem. The software
reassembles the data to reach the end conclusion of the original
complex problem.
 It's a high-tech way of saying that it's easier to get work done if you can
share the load. You could divide the load up among different processors
housed in the same computer, or you could network several computers
together and divide the load up among all of them. There are several
ways to achieve the same goal.
Parallel Processing
 Parallel processing is also called parallel computing. In the quest of
cheaper computing alternatives parallel processing provides a viable
option. The idle time of processor cycles across network can be used
effectively by sophisticated distributed computing software. The term
parallel processing is used to represent a large class of techniques
which are used to provide simultaneous data processing tasks for the
purpose of increasing the computational speed of a computer system.
 With single-CPU, single-core computers, it is possible to perform
parallel processing by connecting the computers in a network.
However, this type of parallel processing requires very sophisticated
software called distributed processing software.
An Arithmetic Logic unit at its most basic level works by using
weighted logic, the binary numbering system is a base 2 numbering
system which is a weighted logic system these values are evaluated
by the ALU using the voltage presented to it by the way the electrical
signal is presented, by the millions of transistors on the chip. A good
way to study this at a basic level would be to start by studying ohms
law and logic probes, an ALU at a basic level.
Short for Arithmetic Logic Unit, ALU is one
of the many components within a computer
processor. The ALU performs mathematical,
logical, and decision operations in a computer
and is the final processing performed by the
processor. After the information has been
processed by the ALU, it is sent to the
computer memory.
A machine cycle, also called a processor cycle or a instruction cycle, is the basic operation performed by a central
processing unit (CPU). A CPU is the main logic unit of a computer.
A machine cycle consists of a sequence of three steps that is performed continuously and at a rate of millions per
second while a computer is in operation. They are fetch, decode and execute. There also is a fourth step, store, in
which input and output from the other three phases is stored in memory for later use; however, no actual
processing is performed during this step.
In the fetch step, the control unit requests that main memory provide it with the instruction that is stored at the
address (i.e., location in memory) indicated by the control unit's program counter.
The control unit is a part of the CPU that also decodes the instruction in the instruction register. A register is a very
small amount of very fast memory that is built into the CPU in order to speed up its operations by providing quick
access to commonly used values; instruction registers are registers that hold the instruction being executed by
the CPU. Decoding the instructions in the instruction register involves breaking the operand field into its
components based on the instructions opcode.
Opcode (an abbreviation of operation code) is the portion of a machine language instruction that specifies what
operation is to be performed by the CPU. Machine language, also called machine code, refers to instructions
coded in patterns of bits (i.e., zeros and ones) that are directly readable and executable by a CPU.
A program counter, also called the instruction pointer in some computers, is a register that indicates where the
computer is in its instruction sequence. It holds either the address of the instruction currently being executed or
the address of the next instruction to be executed, depending on the details of the particular computer. The
program counter is automatically incremented for each machine cycle so that instructions are normally retrieved
sequentially from memory.
The control unit places these instructions into its instruction register and then increments the program counter
so that it contains the address of the next instruction stored in memory. It then executes the instruction by
activating the appropriate circuitry to perform the requested task. As soon as the instruction has been executed,
it restarts the machine cycle, beginning with the fetch step.
The steps performed by the computer
processor for each machine language
instruction received. The machine cycle is a 4
process cycle that includes reading and
interpreting the machine language, executing
the code and then storing that code.
Registers are temporary memory units that store words. The registers
are located in the processor, instead of in RAM, so data can be accessed
and stored faster.
It is in the CPU that most of a computer’s real work gets done. The CPU
has several subparts, including an Arithmetic and Logic Unit (ALU), a
control unit (CU) and registers. The ALU performs basic arithmetic and
compares two values to determine if they are equal or if one is larger. The
control unit manages the movement of data and instructions in the CPU.
The registers come in three main types: data, address and index, which
take part in nearly every aspect of the CPU’s operation. A register’s size
depends on the CPU; simple CPUs have registers that hold eight or 16
data bits, more complex ones have 32, 48 or 64-bit registers.
Most operations are done on registers; the
processor can't directly perform arithmetic in
memory for example. If you want to add 1 to
a memory location, the processor will
normally do this by loading the initial value
from memory into a register, adding 1 to the
register, and then saving the value back to
memory. This of course happens very quickly
and transparently to the programmer.
Every modern PC has multiple system clocks. Each of these vibrates at a specific
frequency, normally measured in MHz (megahertz, or millions of cycles per
second). A clock "tick" is the smallest unit of time in which processing happens,
and is sometimes called a cycle; some types of work can be done in one cycle
while others require many. The ticking of these clocks is what drives the various
circuits in the PC, and the faster they tick, the more performance you get from
your machine (other things being equal).
 The original PCs had a unified system clock; a single clock (running at a very low
speed like 8 MHz) drove the processor, memory (there was no cache back then)
and I/O bus. As PCs have advanced and different parts have gained in speed more
than others, the need for multiple clocks has arisen. A typical modern PC now has
either four or five different clocks, running at different (but related) speeds.
When the "system clock" is referred to generically, it normally refers to the speed
of the memory bus running on the motherboard (and not usually that of the
 The various clocks in the modern PC are created using a single clock generator
circuit (on the motherboard) to generate the "main" system clock, and then
various clock multiplier or divider circuits to create the other signals. The table
below shows the typical arrangement of clocks in a 266 MHz Pentium II PC, and
how they relate to each other:
measured in MHz (megahertz, or millions of cycles per
 The original PCs had a unified system clock; a single
clock (running at a very low speed like 8 MHz) drove
the processor, memory (there was no cache back
then) and I/O bus. As PCs have advanced and different
parts have gained in speed more than others, the
need for multiple clocks has arisen. A typical modern
PC now has either four or five different clocks, running
at different (but related) speeds. When the "system
clock" is referred to generically, it normally refers to
the speed of the memory bus running on the
motherboard (and not usually that of the processor).
Though the term heat sink probably isn't one most people think of when
they hear the word computer, it should be. Without heat sinks, modern
computers couldn't run at the speeds they do. Just as you cool down with
a cold bottle of Gatorade after a high impact workout, heat sinks cool
down your computer's processor after it runs multiple programs at once.
And without a quality heat sink, your computer processor is at risk of
overheating, which could destroy your entire system, costing you
hundreds, even thousands of dollars.
Heat can be transferred in three different ways: convection, radiation
and conduction. Conduction is the way heat is transferred in a solid,
and therefore is the way it is transferred in a heat sink. Conduction
occurs when two objects with different temperatures come into
contact with one another. At the point where the two objects meet,
the faster moving molecules of the warmer object crash into the
slower moving molecules of the cooler object. When this happens, the
faster moving molecules from the warmer object give energy to the
slower moving molecules, which in turn heats the cooler object. This
process is known as thermal conductivity, which is how heat sinks
transfer heat away from the computer's processor.
Heat sinks are usually made of metal, which
serves as the thermal conductor that carries
heat away from the CPU. However, there are
pros and cons to using every type of metal.
First, each metal has a different level of
thermal conductivity. The higher the thermal
conductivity of the metal, the more efficient
it is at transferring heat
A computer port is a type of electronic, software- or programming-related
docking point through which information flows from a program on your
computer or to your computer from the Internet or another computer in a
network. (A network, by the way, is a series of computers that are
physically or electronically linked.)
In computer terms, a computer or a program connects to somewhere or
something else on the Internet via a port. Port numbers and the user's IP
address combine into the "who does what" information kept by every
Internet Service Provider.
Facts about Ports
 Transport Layer protocols, such as the Transmission Control
Protocol (TCP) and the User Datagram Protocol (UDP),
specify a source and destination port number in their packet
headers. A port number is a 16-bit unsigned integer, thus
ranging from 1 to 65535 (port number 0 is reserved and
can't be used). A process associates its input or output
channels via Internet sockets, a type of file descriptor, with
a transport protocol, a port number and an IP address. This
process is known as binding, and enables sending and
receiving data via the network. The operating system's
networking software has the task of transmitting outgoing
data from all application ports onto the network, and
forwarding arriving network packets to a process by
matching the packet's IP address and port number. Only
one process may bind to a specific IP address and port
combination using the same transport protocol. Common
application failures, sometimes called port conflicts, occur
when multiple programs attempt to bind to the same port
numbers on the same IP address using the same protocol.
The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is
used to run motors in disk drives and fans. The main specification of a power
supply is in watts. A watt is the product of the voltage in volts and the current
in amperes or amps. If you have been around PCs for many years, you
probably remember that the original PCs had large red toggle switches that
had a good bit of heft to them. When you turned the PC on or off, you knew you
were doing it. These switches actually controlled the flow of 120 volt power to
the power supply
Today you turn on the power with a little push button, and you turn off the
machine with a menu option. These capabilities were added to standard
power supplies several years ago. The operating system can send a signal to
the power supply to tell it to turn off. The push button sends a 5-volt signal to
the power supply to tell it when to turn on. The power supply also has a circuit
that supplies 5 volts, called VSB for "standby voltage" even when it is officially
"off", so that the button will work. See the next page to learn more about
switcher technology.
Facts about Power Supply
 converts mains AC to low-voltage regulated DC power for the
internal components of a computer. Modern personal computers
universally use a switched-mode power supply. Some power supplies
have a manual selector for input voltage, while others automatically
adapt to the supply voltage.
 Most modern desktop personal computer power supplies conform
to the ATX specification, which includes form factor and voltage
tolerances. While an ATX power supply is connected to the mains
supply, it always provides a 5 V standby (5VSB) voltage so that the
standby functions on the computer and certain peripherals are
powered. ATX power supplies are turned on and off by a signal from
the motherboard.
Expansion Slots
 An opening in a computer where a circuit board can be inserted
to add new capabilities to the computer. Nearly all personal
computers except portables contain expansion slots for adding
more memory, graphics capabilities, and support for special
devices. The boards inserted into the expansion slots are called
expansion boards, expansion cards , cards , add-ins , and add-ons.
 Expansion slots for PCs come in two basic sizes: half- and fullsize. Half-size slots are also called 8-bit slots because they can
transfer 8 bits at a time. Full-size slots are sometimes called 16bit slots. In addition, modern PCs include PCI slots for
expansion boards that connect directly to the PCI bus.
Facts about Expansion Slots
 Expansion slots are on the motherboard and are
visible from the back of your CPU. They are the
ports that allow video cards, graphics cards,
monitor cards and sound cards to go in (just to
name a few). There are many more types of
expansion slots, and as technology changes, new
expansion cards become available.
 In general, the more expansion slots, the more
upgradable the computer. Most expansion slots
connect to one of the many kinds of bus or
sometimes into a proprietary backplane or
motherboard. In laptops and other portable
computers, they are called PCMCIA slots
Expansion Card
 The expansion card (also expansion board, adapter card or
accessory card) in computing is a printed circuit board that can be
inserted into an electrical connector, or expansion slot on a
computer motherboard, backplane or riser card to add functionality
to a computer system via the expansion bus.
 One edge of the expansion card holds the contacts (the edge
connector or pin header) that fit exactly into the slot. They establish
the electrical contact between the electronics (mostly integrated
circuits) on the card and on the motherboard.
 Connectors mounted on the bracket allow the connection of external
devices to the card. Depending on the form factor of the
motherboard and case, around one to seven expansion cards can be
added to a computer system. 19 or more expansion cards can be
installed in backplane systems. There are also other factors involved
in expansion card capacity. For example, most graphics cards on the
market as of 2010 are dual slot graphics cards, using the second
slot as a place to put an active heat sink with a fan.
PC cards works in much the same way that hard discs work. They
are embedded with a memory chip that can be read by either a
laptop or a personal computer. For example, if you are storing
photographs on a PC card, a copy of the photo will be taken from
your PC or laptop and stored into the memory chip of the PC card.
The same process is used for documents that are stored on PC
The computer reads the chip and recognizes it as a place for
storage, enabling documents, photos, etc. to be put on the card.
By the same token, using the same process, photos and
documents can be taken off of the PC card and put onto the
computer's desktop for later use. More technically, the PC cards
use an identical interface that is made up of a 68 pin dual row.
Facts About PC Cards
 Given the wide array of manufacturers, both of notebook
computers and peripherals, this hardware was established to make
sure that a single interface be created that was compatible with
both. This led to the creation of the first PCMCIA or PC Card in 1990.
Even during its early release, the PC Cards became very popular, as
for the first time, mobile users could now attach any number of
needed devices, from modems, to sound cards, hard disks and
network adapters to their laptops. It made the data transfer and
synchronization of relevant information on desktop, laptop and
network computers easy.
A drive bay is a standard-sized area for adding
hardware to a computer. Most drive bays are
fixed to the inside of a case, but some can be
removed. Over the years since the
introduction of the IBM PC, it and its
compatibles have had many form factors of
drive bays. Four form factors are in common
use today, the 5.25", 3.5", 2.5" or 1.8" drive bays.
Info on bays
 Also called the external drive bay.
 Accessible from out side the system unit.
 Also called internal drive bay.
 Concealed on inside of system unit.
 A bus is electrical channels that allow various devices
inside the computer to communicate with each other.
Info on buses
 Bus type determines the type of expansion card you
can add.
 Local bus VESA local bus
 PCI (personal component interconnect)
 Accelerated graphic port. (AGP)
Types of Buses
 System bus. Part of the motherboard that connects the
processor to the main memory
 Expansion bus. Allows the processor to communicate
with peripheral devices.
Special purpose ports
 Types of special purpose ports are MIDI Ports which is
a serial port that connects the system unit to a musical
instrument, such as an electronic keyboard.
Info on special purpose ports
 They allow you to hook up a musical instrument.
 Allows you to hook up a synthesizer which can be
peripheral or chip, creates sound from digital
 The MIDI port also allows you to connect a sound
board so you can control the sound of an instrument
that is being connected to your computer.