System Unit Components

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Chapter 4: System Unit Components


The System Unit

• is a case that contains electronic components of the computer used to process data
• The inside of the system unit on a desktop personal computer includes:
• Drive bay (s)
• Power supply 
• Sound card
• Video card
• Processor
• Memory
• The motherboard is the main circuit board of the system unit
• A computer chip contains integrated circuits

Processor

• also called central processing unit (CPU), interprets and carries out the basic instructions that operate a computer
• contain a control unit and arithmetic logic unit (ALU)
• Multi-core processor
• Dual-core processor
• Quad-core processor
• The control unit is the component of the processor that directs and coordinates most of the operations in the computer.
• The arithmetic logic unit (ALU) performs arithmetic, comparison,and other operations.
• For every instruction, a processor repeats a set of four basic operations, which comprise a machine cycle
• Step 1: The control unit fetches the math problem's instructions and data from memory.
• Step 2: The control unit decodes the math problem's instructions and sends the instructions and data to the ALU.
• The ALU performs calculations on the data.
• Step 4: The results of the math problem are stored in memory.
• Most current personal computers support pipelining.
• Processor begins fetching a second instruction before it completes the machine cycle for the first instruction.
• The processor contains registers,that temporarily hold data and instructions
• The system clock controls the timing of all computer operations
• The pace f the system clock is called the clock speed, and is measured in gigahertz (GHz)
• The leading manufacturers of personal computer processor chips are lntel and AMD.
• Determine how you plan to use a new computer before selecting a processor.
• A processor chip generates heat that could cause the chip to burn up.
• Require additional cooling
• Heat sinks
• Liquid cooling
• Liquid cooling technology
• Parallel processing uses multiple processrs simultaneously to execute a single program or task
• Massively parallel processing involves hundreds or thousands of the processors.

Data  Representation

• Analog signals are continuous and vary in strength and quality.
• Digital signals are in one of two states:on or off.
• Most computers are digital.
• The binary system uses two unique digits (0 and 1）
• Bits and bytes
• A computer circuit represents the 0 or the 1 electronically by the presence or absence of an electrical charge.
• Eight bits grouped together as a unit are called a byte. A byte represents a single character in the computer.
• ASCII (American Standard Code for Information Interchange) is the most widely used coding scheme to represent data.

How a Letter Is Converted to Binary Form and Back

Step 1: A user presses the capital letter T (SHIFT+T keys)on the keyboard,which in turn creates a special code,called a scan code,for the capital letter T.

Step 2: The scan code for the capital letter T is sent to the system unit.

Step 3: The system unit converts the scan code for the capital letter T to its ASCII binary code (01010100) and stores it in memory for processing.

Step 4: After processing, the binary code for the capital letter T is converted to an image and displayed on the output device.

Memory

• consists of electronic components that store instructions waiting to be executed by the processor, data needed by those instructions, and the results pf processing the data.
• Stores three basic categories of items:
• The operating system and other system software
• Application programs
• Data being processed and the resulting information
• Each location in memory has an address
• Memory size is measured in kilobytes (KB or K), megabytes(MB),gigabytes(GB),or terabytes(TB).
• The system unit contains two types of memory:
• Volatile memory
• Loses its contents when power is turned off
• Example includes RAM
• Nonvolatile memory
• Does not lose contents when power is removed
• Examples include ROM,flash memory,and CMOS

How Program Instructions Transfer in and out of RAM

Step 1: When you start the computer,certain operating system files are loaded into RAM  from the hard disk.The operating system displays the user interface on the screen.

Step 2: When you start a Web browser,the program's instructions are loaded into RAM from the hard disk. The Web browser and certain operating system instructions are in RAM. The Web browser window appears on the screen.

Step 3: When you start a paint program,the program's instructions are loaded into RAM from the hard disk.The paint program,along with Web browser and certain operating system instructions,are in RAM.the paint program window appears on the screen.

Step 4: When you quite a program,such as the Web browser,its program instructions are removed from RAM.The Web browser no longer is displayed on the screen.

• Three basic types of RAM chips exist:
• Dynamic RAM (DRAM)
• Static RAM (SRAM)
• Magnetoresistive RAM (MRAM)
• RAM chips usually reside on a memory module and are inserted into memory slots.
• The amount  of  RAM necessary in a computer often depends on the types of software you plan to use
• 2 GB or less
• Home and business users ,managing personal finances;using standard application software such as word processing;using educational or entertainment optical discs;communicating with others on the Web.
• 2 GB to 8 GB
• Users requiring more advanced multimedia capabilities;running number-intensive accounting, financial, or spreadsheet programs;using voice recognition;working with videos,music, and digital imaging;creating Web sites; participating in video conferences;playing internet games.
• 8 GB and up
• Power users creating professional Web sites;running sophisticated CAD, 3-D design, or other graphics-intensive software.
• Memory cache speeds the processes of the computer because it stores frequently used instructions and data.
• Read-only memory (ROM) refers to memory chips storing permanent data and instructions.
• A PROM (programmable read -only memory)chip is a blank ROM chip that can be written to permanently.
• Flash memory can be erased electronically and rewritten.
• CMOS technology provides high  speeds and consumes little power.
• Access time is the amount of time it takes the processor to read from memory.
• Measured in nanoseconds

Expansion Slots and Adapter Cards

• An expansion slot is a socket on the motherboard that can hold an adapter card.
• An adapter card enhances functions of a component of the system unit and/or provides connections to peripherals
• Sound card and video card
• With Plug and Play, the computer automatically can configure adapter cards and other peripherals as you install them.
• Removable flash memory includes:
• Memory cards,USB flash drives,and PC Cards/Express Card modules

Ports and Connectors

• A port is the point which a peripheral attaches to or communicates with a system unit (sometimes referred to as a jack)
• A connector joins a cable to a port.
• On a notebook computer, the ports are on the back, front,and/or sides.
• A USB port can connect up to 127 different peripherals together with a single connector.
• You can attach multiple peripherals using a single USB port with a USB hub.
• Other types of ports include:
• Firewire port
• Bluetooth port
• SCSI port
• ESATA port
• lrDA port
• Serial port
• MIDI port
• A Bluetooth wireless port adapter converts a USB port into  a Bluetooth port.
• A smart phone might communicate with a notebook computer using an lrDA port.
• A port replicator is an external device that provides connections to peripherals through ports built into the device.
• A docking station is an external device that attaches to a mobile computer or device.

Buses

• A bus allows the various devices both inside and attached to the system unit to communicate with each other
• Data bus
• Address bus
• Word size is the number of bits the processor can interpret and execute at a given time.
• Expansion slots connect to expansion buses
• Common types of expansion buses include:
• PCI bus
• PCI Express bus
• Accelerated Graphics Port
• USB and Firewire bus
• PC Card bus

Bays

• A bay is an opening inside the system unit in which you can install additional equipment
• A drive bay typically holds disk drives.

Power Supply

• The power supply converts the wall outlet AC power into DC power.
• Some external peripherals have an AC adapter,which is an external power supply.

Putting It All Together

• Home
• Intel Core i5
• Intel Core 2 i3
• AMD Athlon II
• AMD Sempron
• Minimum RAM:2 GB
• Small office/Home office
• Intel Core i7
• Intel Core i7 Extreme
• AMD Phenom II
• AMD Athlon II
• Minimum RAM : 4 GB
• Mobile
• INtel Core i7 Extreme
• Intel Core i7
• AMD Phenom II
• AMD Turion II
• Minimum RAM: 2 GB
• Power
• Intel Xeon 
• Intel Itanium 
• AMD Opteron
• Minimum RAM:8 GB
• Enterprise
• Intel Core i7
• Intel Core i7 Extreme
• AMD Phenom II
• AMD Athlon II
• Minimum RAM: 4 GB

Keeping Your Computer or Mobile Device Clean

• Clean your computer or mobile device once or twice a year
• Turn off and unplug your computer or mobile device before cleaning it.
• Use compressed air to blow away dust.
• Use an antistatic wipe to clean the exterior of the case and a cleaning solution and soft cloth to clean the screen.