• An electronic component that interprets and
carries out the basic instructions that operate
• Also called Central Processing Unit (CPU).
• contains two components:
– control unit
– arithmetic logic unit (ALU)
• A component of the processor that directs and
coordinates most of the operations in the
• Has a role like a traffic cop.
• Interprets each instruction of a program, and
then initiates the appropriate action to carry
out the instruction.
Arithmetic Logic Unit
• A component of the processor that performs
arithmetic, comparison and other operations.
– Arithmetic operations are +, -, *, /
– Comparison operations are > , >=, <, <=, =, ≠
• A set of four basic steps performed by a
processor every time it executes one
• The four basic steps are:
Steps in a Machine Cycle
1) Fetch - Control unit fetches the instruction
and data from memory.
2) Decode - Control unit interprets the
instruction and sends the instruction and
data to the ALU.
3) Execute - ALU performs calculations on the
4) Store - The results of the calculations are
stored in the 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.
• Usually consists of one or more chips on the
motherboard or some other circuit boards in
• Memory that loses its contents when the
power is turned off.
• Example: RAM
• Memory that does not lose its contents when
the power is turned off.
• Example: ROM, flash memory, and CMOS.
Types of Memory
• Random access memory (RAM)
• Read only memory (ROM)
Types of Memory: RAM
• Memory chips that holds data or programs
that are currently being used by the processor
• Can be read from and written to by the
• Volatile - loses its contents when the power is
SRAM (Static RAM) - Do not have to be reenergized
as often as DRAM chips, faster access time,
more reliable but more expensive than DRAM.
MRAM (Magnetoresistive RAM) - Stores data
using magnetic charges instead of electrical charges,
greater storage capacity, consume less energy, faster
access time, more expensive, and non-volatile
DRAM (Dynamic RAM) - Chips must be reenergized
constantly to keep their contents.
Types of Memory: ROM
• Memory chips that stores permanent data or
instructions needed by a computer or devices.
• Can be read from, but cannot be written to by
• Non volatile – does not lose its contents when
the power is turned off.
EPROM (Erasable Programmable ROM) -
Allows the programmer to erase the contents by
exposing to ultraviolet light.
EEPROM (Electrically Erasable Programmable
ROM) - Allows the programmer to erase the
contents with an electric signal.
PROM (Programmable ROM) - A blank ROM chip
which a programmer can write permanently; once
written, the contents cannot be erased or changed
• Main circuit board of the system unit.
• The functions of the motherboard:
– Holds various components of the system.
– Provides connectors for other peripherals.
Components of a Motherboard
• Processor Slot
• Memory Slot
• Adapter Card Slot
• SATA connector
• BIOS chip and battery
• Power connector
Adapter Card Slot
• Slots on the motherboard that hold adapter
• Adapter card slots are also called expansion
– To connect devices such as network cards, sound
cards, modems, extra ports such as USB or serial
TV tuner cards and disk controllers.
– Specifically designed to connect graphic adapters.
• Slots on the motherboard that hold memory
• Memory module is a small circuit board that
holds RAM chips.
A slot on the motherboard that holds a