Central processing Unit
(CPU)
Control Unit
• The central processing unit (CPU) also called a processor, is the unit
that performs most of the processing in the computer.
• The CPU contains the arithmetic/logic unit.
• The control unit directs and coordinates most of the operations in the
computer.
• For every instruction, these units repeat a set of four basic operations
called the machine cycle.
Machine cycle:
1. Fetching the instruction or data item from memory
2. Decoding the instruction into commands the computer
understands
3. Executing the commands, and, if necessary,
4. Storing, or writing the result on memory
Memory
• From the moment you turn on the computer until you shut it
down, the CPU constantly uses memory. It is a very important
component to a computer.
• Data is stored in memory chips. This makes it possible for the
computer to remember the data it is working on.
• There are two types of internal memory:
1. RAM (Random Access Memory)
2. ROM (Read-Only Memory)
RAM (Random Access Memory)
• It is internal memory used for temporary storage of information.
• It is volatile – once the computer is powered off it losses the data.
• You can read and write through this memory
ROM (Read-Only Memory)
• It is the internal and permanent memory used at start-up
• It is non-volatile. It keeps data even when the computer is powered
off.
• We can read only this memory and cannot write through it.
Processor speed
• CPU clock speed, or clock rate is a measure of how many clock cycles
a CPU can perform per second.
• It is measured in Hertz, generally in gigahertz (GHz)
Types of processors
1. Multi-core processor – is a single computing component with two
or more independent actual central processing units (called cores)
2. Dual-core processors- are CPUs which have two physical and
independent processing units within them, i.e. two cores.
Examples; Intel core i5, Intel Core 2 Duo and Pentium Dual Core
processors.
3. Quad-core processors- are CPUs with four units within them.
Examples; Intel core i7, AMD Phenom processors.
ALU and Control unit
• The CPU has two parts
1. ALU (Arithmetic Logic Unit)
 Performs arithmetic operations
 Performs logic operations
 Uses registers to hold data being processed
2. Control Unit
 Directs and coordinates processing
Computer storage devices
• Storage media or storage devices – are items used to store any
amount of data for future use.
• Computer memory is measured in bytes (B), kilobytes (KB),
megabytes (MB),gigabytes (GB), etc
Computer memory is classified into three categories.
1. Primary memory
2. Secondary memory
3. Virtual memory
Primary memory
• Is the main memory of the computer where the currently
processing data resides.
• primary memory is directly accessible by CPU
• Primary memory is an internal memory
• Primary memory is non-removable.
• RAM (random access memory), ROM and cache are examples of
a primary storage device.
• cache is a high-speed access area that can be a reserved section of
main memory or on a storage device.
Secondary memory
• The secondary memory of the computer is also known as an auxiliary
memory
• secondary memory is not directly accessible to CPU.
• secondary memory is an external memory.
• Examples include hard disk, floppy disk, CD, DVD, Memory cards,
etc.
Virtual memory
• Is a memory management capability of an operating system (OS) that
uses hardware and software to allow a computer to compensate for
physical memory shortages by temporarily transferring data from
random access memory (RAM) to disk storage.
Activity
1. List and describe the three computer memory you have learnt about
give examples where necessary
(6)
2. Describe the following properties of storage media
A. Volatile and Non-volatile
(2)
B. Internal and External
(2)
Cables and ports
A computer port is a connection point or interface between
a computer and an external or internal device.
 Internal ports may connect such devices as hard drives and CD ROM
or DVD drives
 external ports may connect modems, printers, mice and other
devices.
A cable (also known as a cord) is one or more wires covered in a
plastic covering that allows for the transmission of power or data
between devices.
Computer ports
Computer cables
Identify cables in picture below