1. COMPONENTS
OF A
PERSONAL
COMPUTER

2. A typical personal computer has hard, floppy and CD-ROM disks for storage, memory and CPU chips inside the system unit, a keyboard and mouse for input, and a display, printer and speakers for output.
Computer systems ranging from a microcomputer to a large supercomputer contain components providing five functions.
The arrows represent the direction information flows between the functional units.

3. If you use a desktop computer, you might already know that there isn't any single part called the "computer.".
A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware.
Software, on the other hand, refers to the instructions, or programs, that tell the hardware what to do

4. The main elements of a PC are:
Input/Output
Memory
Central Processing Unit (CPU)
Storage

5. INPUT DEVICES
An input device is any hardware component that allows user to enter data and instructions into a computer.
Examples of widely used input devices are keyboard, mouse, microphone, scanner and web cam.
A keyboard contains keys you press to enter data into the computer.
A mouse is a small handheld devices. User control movement of a small symbol on the screen called the pointer and make selections from the screen.

6. INPUT DEVICES A microphone allows you to speak into the computer.
A scanner converts printed material such as text and pictures into a form the computer can use.
A Web cam is a digital video camera that allows user to create movies or take pictures and store them on the computer.

7. OUTPUT DEVICES
An output device is any hardware component that conveys information to one or more people.
Three of the commonly used output devices are printer, monitor and speaker.
A monitor display text, graphics and videos on a screen.
A printer produces text and graphics on a physical medium such a paper.
A speaker allow user to hear music and other audio (sounds).

8. STORAGE DEVICES
A storage device holds data, instructions and information for future use. These items are stored permanently.
A storage device records (writes) and/or retrieves (reads items to and from storage media.)
Examples of storage media are USB flash drives, hard disks, optical disks and memory cards.
A USB flash drive is a portable storage device. The average USB flash drive can hold about 4 billion characters.

9. STORAGE DEVICES
A hard disk provides much greater storage capacity that a USB flash drive. The average hard disk can hold more than 320 billion characters.
Hard disks are enclosed in an airtight, sealed case. Although some are portable, most are housed inside the system unit.
Portable hard disks are external or removable.

10. STORAGE DEVICES
An optical disc is a flat, round, portable metal disc with a plastic coating. CDs, DVDs, and Blu-ray Discs are three types of optical discs.
A CD can hold from 650 million to 1 billion characters.
Some DVDs can store two full-length movies or 17 billion characters.
Blu-ray discs can store about 46 hours of standard video or 100 billion characters.

11. PROCESSOR (CPU)? What is a
Also called the central processing unit (CPU), a processor interprets and carries out the basic instructions that operate a computer.
The processor impacts overall computing power and manages most of a computer’s operations.

12. On a PC, all functions of the processor usually are on a single chip.
Some computer and chip manufacturers use the term microprocessor to refer to a personal computer processor chip.
Most processor chip manufacturers now offer multi-core processors.
A processor core contains circuitry necessary to execute instructions. The OS views each processor core as a separate processor.

13. A multi-core processor is a single chip with two or more separate processor cores.
Two common multi-core processors are dual-core and quad-core.
A dual-core processor is a chip that contains two separate processor cores.
A quad-core processor is a chip with four separate processor cores.
Each processor core on a multi-core processor generally runs at a slower clock speed than a single-core processor, but multi-core processors typically increase overall performance

14. For example, although a dual-core processor does not double the processing speed of a single-core processor, it can approach those speeds.
The performance increase is especially noticeable when users are running multiple programs simultaneously such as antivirus software, spyware remover, -program, media player and etc.
Multi-core processors also are more energy efficient than separate multiple processors, requiring lower levels or power consumption and emitting less heat in the system unit.
A processor contains a control unit and arithmetic logic unit (ALU). These two components work together to perform processing operations.

16. Control Unit (CU)
The control unit is the component of the processor that directs and coordinates most of the operations in the computer.
The control unit has a role much like a traffic cop – it interprets each instruction issued by a program and then initiates the appropriate action to carry out the instruction.

17. Arithmetic & Logic Unit (ALU)
Arithmetic logic unit (ALU) is another component of the processor that performs arithmetic, comparison and logical operations.
Arithmetic operations include basic calculations such as addition, subtraction, multiplication and division.
Comparison operations involve comparing one data item with another to determine whether the first item is greater than, equal to or less than the other item.
Logical involves operations such as AND, OR, NOT.

18. The ALU executes the arithmetic or logical instruction.
How the CPU Executes Program
Instructions?
Before an instruction can be executed, program instructions
and data must be placed into memory from an input device
or a secondary storage device. Once the necessary data and
instruction are in memory, the central processing unit
performs the following FOUR steps for each instruction:
STEP 2:
The control unit decodes the instruction (decodes what it means) and directs the necessary data to be moved from memory to the ALU.
STEP 3:
The ALU executes the arithmetic or logical instruction.
That is, the ALU is given control and performs the actual operation on the data.
STEP 4:
The ALU stores the result of this operation in memory or in a register.
STEP 1:
The control
unit fetches
(gets) the
instruction
from memory.

19. STEP 1 & STEP 2 together are called
instruction time, or I-time.
STEP 3 & STEP 4 together are called
Execution time, or E-time.

20. Registers
A processor contains small, high-speed storage locations called registers that temporarily hold instructions or data.
Registers are part of the processor. They are NOT a part of memory or a permanent storage device.
Processors have many different types of registers each with a specific storage functions.
Register functions include storing the location from where an instruction was fetched, storing an instruction while the CU decodes it and storing the results of a calculation.

21. MEMORY
Memory consists of electronic components that store instructions waiting to be executed by the processor, data needed by those instructions and the results of processing the data (information). Memory usually consists of one or more chips on the motherboard or some other circuit board in the computer.
Memory stores three basic categories of items:
The operating system and other system software that control or maintain the computer and its devices
Application programs that carry out a specific task such as word processing
The data being processed by the application programs and resulting information.

22. TYPES OF MEMORY
The system unit contains two types of memory: volatile and nonvolatile.
When the computer’s power is turned off, volatile memory loses its contents. Volatile memory is temporary. Example is RAM.
Nonvolatile memory does not lose its contents when power is removed from the computer. Nonvolatile memory is permanent. Examples are ROM, flash memory and CMOS.

23. RAM (RANDOM ACCESS MEMORY)
Random-access, commonly known as RAM or main memory, consists of memory
RAM is volatile; data stored in RAM stays there only as long as the computer is running. As soon as the computer is switched off, the data stored in RAM disappears.

25. RAM (RANDOM ACCESS MEMORY)
There are two different types of RAM:
DRAM (Dynamic Random Access Memory)
SRAM (Static Random Access Memory)
MRAM (Magnetoresistive Random Access Memory).
SRAM
faster and more reliable than the more common DRAM
doesn't need to be refreshed like dynamic RAM.
Volatile
It is used primarily for cache.
MRAM
stores data using magnetic charges instead of electrical charges
has greater storage capacity, consumes less power, has faster access times
MRAM
Retain its contents after power is switch off
DRAM
requires constant refreshing or they lose their contents
Volatile
DRAM is used
in main
memory

26. RAM (RANDOM ACCESS MEMORY)

27. CACHE
Most of today’s computers improve their processing times with cache.
Two types of cache are memory cache and disk cache.
Memory cache helps speed the processes of the computer because it stores frequently used instructions and data.
Most PCs today have two types of memory cache:
L1 cache
L2 cache
Some also have L3 cache.

28. CACHE L1 CACHE: L1 cache is built directly in the processor chip.
It usually has a very small capacity, ranging from 8KB to 128KB.
L2 CACHE:
L2 cache is slightly lower than L1 cache but has a much larger capacity ranging from 64 KB to 16 MB.
When discussing cache, most users are referring to L2 cache.

30. ROM (READ ONLY MEMORY)
Read-Only Memory (ROM) is an integrated-circuit memory chip that contains configuration data.
ROM is used in most computers to hold a small, special piece of software: the 'boot up' program. This software runs when the computer is switched on or 'boots up'. The software checks the computer’s hardware and then loads the operating system.

31. ROM (READ ONLY MEMORY)
Data stored in ROM is nonvolatile - it is not lost when your computer is turned off.
Data stored in ROM is either unchangeable or requires a special operation to change.
Examples of ROM are: Programmable ROM (PROM), Erasable Programmable ROM (EPROM) and Electrically Erasable Programmable ROM (EEPROM).

32. FLASH MEMORY
Flash memory is a type of nonvolatile memory that can be erased electronically and rewritten.
Most computers use flash memory to hold their startup instructions because it allows the computer easily to update its contents.
Example, when the computer changes from standard time to daylight savings time, the contents of a flash memory chip change to reflect the new time.

33. FLASH MEMORY
Flash memory chips also store data and programs on many mobile computers and devices such as smart phones, portable media players, PDAs, printers, digital cameras, etc.

36. CMOS
Some RAM chips, flash memory chips and other memory chips use complementary metal-oxide semiconductor (CMOS) technology because it provides high speeds and consumes little power.
CMOS technology uses battery power to retain information even when the power of the computer is off.
The flash memory chips that store a computer’s startup information often use CMOS technology.