Computer Systems
A computer system requires many components to do its job:
It requires some device or method to input data so it can be processed.
It requires circuit boards and programs to process the data.
It needs some type of output device to display the result of its processing.
It needs some mechanism for storing data.
Common System Components
This figure shows several devices that are common components of a computer system.
System Motherboard
The motherboard contains the electronic circuitry of the computer.
Components found on the motherboard include:
The primary processing chip (CPU)
The memory chips
Expansion slots for system interface cards
Ports for connecting external devices
BIOS chips that control system startup
The circuitry that enables all of these components to communicate
The Central Processing Unit
The CPU is the brains of a computer system.
The CPU is housed on a silicon chip that contains millions of switches and circuits.
The CPU has two primary sections:
Arithmetic/logic unit (ALU)
o This section performs arithmetic and logical operations.
Control unit
o This section is the boss of the CPU and coordinates all activity within the CPU.
o It uses programming instructions to control what actions the CPU performs and when it performs them.
The CPU determines which of the millions of switches that it contains should be turned on or off by processing program statements that tell it what to do.
Computer programs are written in programming languages.
Each program statement causes one or more actions to occur in the CPU.
Computer Memory
Data being processed by a CPU is stored in system memory.
Memory consists of addressable locations within the machine that the computer can access directly.
Data stored in memory is volatile.
o If the power fails, everything in memory is lost.
Data must be stored on a disk or some other device when not being processed so it is not lost each time the computer shuts down.
Types of Memory
RAM—Random Access Memory
o RAM is short-term memory in which data is processed while a program is running.
o Data stored here can be accessed and modified as needed.
o This type of memory loses any data it holds if the computer is shut down.
o
ROM—Read-Only Memory
o ROM is memory placed on the motherboard by the manufacturer and contains instructions that tell the computer how to start itself.
o This data cannot be accessed or modified by application programs.
o The contents of this memory are not lost when the computer is shut down.
The Machine Cycle
The instruction cycle and one or more execution cycles create a machine cycle.
Machine cycles are measured in microseconds.
The faster your computer can process machine cycles, the faster it can process data.
The instruction cycle is the amount of time required to read and decode the instruction.
The execution cycle is the amount of time required to execute the instruction and store the results.
Computer System Controllers
A PC motherboard contains several controllers.
Controllers are devices that control the transfer of data between the computer and peripheral devices.
Common peripheral devices include a mouse, monitor, printer, keyboard, and so on.
Controllers usually are found on a single chip that can handle all common devices.
Ports
Serial and parallel ports are used to connect peripheral devices to the computer circuitry.
o Serial devices (mice/monitors) transmit data one bit at a time.
o Parallel devices (printers) transmit data several bits at time.
USB is a newer, high-speed method of connecting devices and is beginning to replace serial and parallel ports.
o USB can connect up to 127 external devices.
Firewire is another high-speed method.
o Firewire can connect up to 63 external devices.
Expansion Slots
Expansion slots are electrical connections in the motherboard that can accept circuit cards to perform specific functions.
These commonly are used to plug in sound cards, video cards, scanners, and other devices.
Data Representation
Data is stored in a computer in binary format as a series of 1s and 0s.
Computers use standardized coding systems (such as ASCII) to determine what character or number is represented by what series of binary digits.
Data is stored in a series of 8-bit combinations called a byte.
Every letter, number, punctuation mark, or symbol has its own unique combination of 1s and 0s.
Just about all computers perform the same general options: input, processing, output, and storage.
Input, output, and processing devices grouped together represent a computer system.
The motherboard is the center of all processing.
The motherboard contains the CPU, memory, and basic controllers for the system.
The motherboard also contains ports and expansion slots.
The central processing unit is the brains of the computer.
The computer is given instructions through computer programs.
The CPU has two main sections—the arithmetic logic unit and the control unit.
All calculations and comparisons take place in the ALU.
The control unit coordinates the CPU activities.
The motherboard contains different types of memory.
The machine cycle is made up of the instruction cycle and the execution cycle.
Random access memory is volatile and is used to store instructions, data, and information temporarily.
Read-only memory is nonvolatile and is used to store permanent instructions needed for computer operations.
A controller is used to control the transfer of data between the computer and peripheral devices.
Expansion slots contain expansion boards.
Expansion boards are used to connect specialized peripheral devices or to add more memory to the computer.
Peripheral devices are connected to the computer through serial and parallel ports.
The Universal Serial Bus is a newer standard expected to replace serial and parallel ports.
FireWire is a type of external bus that can connect up to 63 external devices.
SCSI, IrDA, and Bluetooth are special-purpose ports.
The ASCII and EBCDIC codes are standard codes used to represent the alphabet, numbers, symbols, and punctuation marks.
