Central Processing Unit (CPU)
The Central Processing Unit (CPU) also called microprocessor,
computer processor or simply processor is the main part of a computer that
carries out all the instructions of a program.
It is often called the “brain of the computer” because it
controls all the operations, processes data, and manages communication between
the computer’s hardware and software.
In simple terms, the CPU carry out the following functions:
- Fetches
instructions from memory.
- Decodes
them to understand what action is needed.
- Executes
the instructions.
- Stores
the results back in memory if needed.
The central processing unit (CPU) carries out each function or instruction
in sequence. The CPU is located on the motherboard, and all of its functions
are handled by a component called the chip or microprocessor. The CPU is the
most important part of a computer, regardless of its size. It controls
everything—from the operating system and software to games and hardware.
The CPU is responsible for instructing the computer on what to do and
when, such as connecting to the internet or writing a document. It performs all
the analytical, computational, and logical operations that occur within the
computer.
CPU speed is measured in cycles per second, which determines how quickly
it can execute instructions. This is commonly referred to as clock speed. The
more cycles the CPU performs per second, the more instructions it can process,
and the faster the computer operates.
The first Intel CPU operated at a speed of 108 kHz, or 108,000 cycles per
second. Today, however, CPUs are far more powerful, with speeds reaching as
high as 3.5 GHz—or 3.5 billion cycles per second.
Types of CPU
CPU can be group by the
Number of Cores as follows:
·
Single-core CPU → one
processing unit; older and slower at multitasking.
·
Dual-core CPU → two cores in
one chip; can handle more tasks at once.
·
Quad-core CPU → four cores,
common in modern PCs.
·
Hexa-core, Octa-core, Deca-core
→ 6, 8, or 10 cores; found in high-performance computers and smartphones.
·
Multi-core CPUs → general term
for CPUs with multiple cores, used in servers and powerful workstations.
Components of the CPU
The main components of the CPU (Central Processing Unit) are:
1. Arithmetic
and Logic Unit (ALU) – performs all arithmetic (addition, subtraction, etc.)
and logical operations (comparisons like greater than, equal to, etc.).
2. Control
Unit (CU) – directs the flow of data and instructions, coordinating the
activities of all parts of the computer.
3. Registers
– Registers are a type of internal CPU memory. It is the smallest and fastest
type of memory inside the CPU, used to hold instructions, addresses, or data
that the processor is actively working on. Data only stays there while being
processed.
Other components are:
1. Cache
Memory –Cache is a small, high-speed memory located inside or very close to the
CPU, used to store frequently used data and instructions so the processor can
retrieve them faster than from RAM.
The Cache is an Intermediate memory
between registers and RAM. It is larger and slower than registers but faster
and smaller than RAM .
The level of cache are: L1 (smallest, fastest, built into CPU core), L2 (larger,
slightly slower), L3 (even larger, shared across cores).
The
cache is a Volatile memory: like
RAM, cache is cleared when power is turned off.
2. Clock
– provides timing signals that synchronize all operations of the CPU.
Functions
of the Arithmetic and Logic Unit
The Arithmetic and Logic Unit (ALU) is the part of the CPU
responsible for all calculations and decision-making. Its main functions are:
- Arithmetic operations
– carries out mathematical operations such as addition, subtraction,
multiplication, and division.
- Logic operations
– performs comparisons like equal to (=), greater than (>), less than
(<), and not equal to (≠).
- Bitwise operations
– manipulates data at the binary (bit) level, such as shifting bits
left/right or AND, OR, NOT operations.
- Decision-making support
– helps the CPU decide the next step in processing based on logical test
results (e.g., if a condition is true or false).
- Data transfer operations
– temporarily moves data between registers or to/from memory during
processing.
Functions of the Control Unit
(CU):
- Instruction Fetching
– retrieves instructions from the main memory.
- Instruction Decoding
– interprets (decodes) the instructions to understand what action is
required.
- Control of Data Flow
– directs the movement of data between the CPU, memory, and input/output
devices.
- Coordination of
Components – ensures that the ALU,
registers, and other components work together in the right order.
- Execution Control
– tells the ALU when to perform operations and ensures results are stored
in the correct place.
- Maintains Sequence
– ensures instructions are executed step by step in the proper sequence
unless told otherwise (like in jumps or loops).
The Register: Registers
are small, high-speed storage units inside the CPU that keep
track of instructions, data, addresses, and results during processing.
Functions of Registers
in the CPU:
- Temporary Storage
– hold data, instructions, and memory addresses being used by the CPU.
- Fast Access
– provide very quick read/write access compared to main memory (RAM).
- Instruction Holding
– keep the current instruction being executed (e.g., in the Instruction
Register).
- Address Holding
– store the address of the next instruction or data in memory (e.g.,
Program Counter, Memory Address Register).
- Data Holding
– store data being transferred to/from memory or the ALU (e.g., Memory
Data Register, Accumulator).
- Control Information
– some registers hold status flags that show the result of operations
(e.g., zero, carry, overflow, negative).
Types of registers in the CPU
and their functions
1.
Program Counter (PC)
- Holds the address of the next instruction
to be executed.
- Updates automatically after each instruction.
2.
Instruction Register (IR): Stores the current
instruction that the CPU is decoding and executing.
3.
Memory Address Register (MAR): Holds the address in
memory where data or an instruction needs to be fetched or stored.
4.
Memory Data Register (MDR)
(also called Memory Buffer Register, MBR)
- Temporarily holds the data being transferred
to or from memory.
5.
Accumulator (ACC)
- Stores intermediate arithmetic and logic
results produced by the ALU.
6.
General Purpose Registers
(e.g., AX, BX in older CPUs)
- Used by the CPU to hold temporary data,
variables, or intermediate results during processing.
7.
Status Register / Flag Register
- Contains flags (bits) that show the
results of operations, such as:
- Zero flag (result is zero)
- Carry flag (carry generated in addition)
- Sign flag (positive/negative result)
- Overflow flag (arithmetic overflow)
Memory Unit
The Memory Unit Is the part of a computer that stores data and instructions,
either temporarily or permanently, for use by the CPU and other components. It
stores instructions that the CPU needs to execute. The memory unit is made of
internal memory which consist of the Register and the Cache and the external
memory which consist of the main memory and the auxiliary memory
.
Functions of the Memory Unit in a computer
1. Storage
of Instructions – keeps the programs and instructions that the CPU will
execute.
2. Storage
of Data – holds the data that is being processed by the CPU.
3. Storage
of Results – saves the output produced after processing, before sending it to
output devices.
4. Data
Transfer – transfers data and instructions to and from the CPU as needed.
5. Program
Execution Support – ensures instructions are available in the correct sequence
for execution.
Types of Memory
a. Primary
memory (Main Memory)
b. Secondary
memory (Auxiliary Memory)
a. Primary Memory: The Primary Memory also called main memory is the part of
the memory unit that directly stores data and instructions the CPU needs while
working.
The primary memory is fast much faster than secondary storage like hard
drives and it is directly accessible by the CPU (the CPU fetches instructions
and data from it).
Types of Primary Memory
1. RAM
(Random Access Memory)
2. ROM
(Read Only Memory)
1. RAM (Random Access Memory): This is a volatile memory used by computers to
store data that the CPU needs quickly. It is connected to the CPU through a
memory bus.
Key characteristics and function
1. It
is a temporary storage.
2. It
Stores data and instructions currently being used by the CPU.
3. Volatile
(data disappears when power is off).
4. More RAM means more
applications/data your system can handle at once without slowing down.
5. Multiple apps stay open
smoothly if enough RAM is available.
6. Improves performance for
games, video editing, and large file processing
Types
of RAM
Main Categories
of RAM are
a. DRAM (Dynamic RAM)
- Made
of memory cells which are composed of one capacitor and one transistor.
- Stores
each bit as a charge in a tiny capacitor.
- Needs
to be refreshed thousands of times per second in order to maintain data.
- Cheap & high-density,
but slower compared to other types.
- Used
in main system memory.
b. SRAM (Static RAM)
- Retains
its contents as long as the power is being supplied
- Stores
data using flip-flops (doesn’t need refreshing).
- Faster and more reliable than DRAM.
- Uses
a matrix of 6-transistors and no capacitors
- More
expensive & lower density → not used for main memory.
- Found
in CPU caches (L1, L2, L3).
2. ROM (Read Only Memory): This
is a non-volatile (data stays even when power is off). It is
traditionally pre-programmed with permanent instructions that cannot
be modified (or only modified with special methods).
Key characteristics and functions
1. Permanent
storage.
2. We
can only read but cannot write on it.
3. Stores
essential programs like the BIOS needed to start the computer.
4. Non-volatile
(data stays even when power is off).
- Provides
a permanent program for devices like printers, calculators, embedded
systems.
- Ensures
critical instructions are safe from being deleted or changed accidentally.
Types of ROM
- MROM
(Masked ROM)
- Data is written during manufacturing.
- Cannot be changed later.
- Cheap, but inflexible.
- PROM
(Programmable ROM)
- Can be written once by the user (with special
hardware).
- Once programmed, cannot be erased.
- EPROM
(Erasable Programmable ROM)
- Can be erased by UV light and reprogrammed.
- Reusable, but slow and inconvenient.
- EEPROM
(Electrically Erasable Programmable ROM)
- Can be erased and reprogrammed using electricity.
- More flexible, often used for firmware updates.
- Flash
Memory (a type of EEPROM)
- Can be rewritten many times quickly.
- Used in USB drives, SSDs, memory cards, BIOS chips.
Difference Between RAM and ROM
|
Feature
|
RAM (Random Access Memory)
|
ROM (Read Only Memory)
|
|
Nature
|
Temporary memory (volatile)
|
Permanent memory (non-volatile)
|
|
Data Retention
|
Data is lost when power is off
|
Data is retained even when power is off
|
|
Function
|
Stores data and instructions the CPU is currently using
|
Stores essential programs and instructions needed for booting (e.g., BIOS)
|
|
Read/Write
|
Both read and write operations are possible
|
Usually read-only (cannot be modified easily)
|
|
Speed
|
Very fast
|
Slower compared to
RAM
|
|
Data input
|
The data is
usually inputed by the manufacturer.
|
The data is
usually inputted by the user
|
|
Example Use
|
Running applications, files in use, active processes
|
Boot-up firmware, embedded system instructions
|
Difference
between Registers and Main Memory
|
Feature
|
Registers
|
Main Memory (Primary Memory –
RAM/ROM)
|
|
Location
|
Inside the CPU.
|
Outside the CPU but directly
connected to it.
|
|
Speed
|
Extremely fast (fastest storage in
the computer).
|
Fast, but slower than registers.
|
|
Size/Capacity
|
Very small (measured in bits or
bytes).
|
Much larger (measured in GBs).
|
|
Function
|
Holds instructions, addresses, or
data that the CPU is currently processing.
|
Stores programs, data, and
instructions that the CPU may need.
|
|
Accessibility
|
Directly accessed by the CPU
without delay.
|
CPU must fetch data from main
memory, which takes more time.
|
|
Volatility
|
Volatile (contents lost when power
is off).
|
RAM is volatile, ROM is
non-volatile.
|
b. Secondary
Memory
The Secondary Memory (also called auxiliary storage or external memory) is
the type of computer memory used to store data, programs, and files permanently
for long-term use.
Key characteristics
and functions
1. Non-volatile
– data is not lost when the power is turned off.
2. Larger
in capacity – can store much more data than primary memory.
3. Slower
in speed – accessing data takes more time compared to RAM.
4. Not
directly accessed by the CPU – data must first be loaded into primary memory
before the CPU can use it.
5. Keeps
data and programs even when the computer is turned off (non-volatile).
6. Stores
copies of important files to protect against data loss.
7. Large
Capacity Storage: Holds much more data than primary memory (RAM).
8. Allows
files to be moved between devices (e.g., flash drives, memory cards).
9. Preserves
data for long-term use, especially with media like magnetic tapes and optical
discs.
Examples
of Secondary Memory:
Here’s a brief description of each secondary storage device:
- Hard Disk Drives (HDDs) – Magnetic storage devices with
spinning platters and read/write heads; they offer large capacity at low
cost but are slower and more fragile compared to SSDs.
- Solid State Drives (SSDs) – Use flash memory (no moving
parts) to store data; they are much faster, more durable, and
energy-efficient than HDDs, but generally more expensive per GB.
- Optical Discs (CDs, DVDs,
Blu-ray) – Use lasers to read/write data on discs; mainly used for media
distribution and backup, but less common today due to limited capacity and
slower speeds.
- Flash Drives / Pen Drives – Portable USB-based flash
memory devices; small, lightweight, and convenient for transferring files
between computers.
- Memory Card – Small flash memory storage
used mainly in smartphones, cameras, and other portable devices; compact
and easily removable.
- Magnetic Tapes – Long strips of magnetic
material used for sequential data storage; very high capacity and
cost-effective for backups and archiving, though slower to access.
Comparison
Between Primary Memory and Secondary Memory
|
Feature
|
Primary Memory
|
Secondary Memory
|
|
Definition
|
The computer’s main memory directly accessed by the CPU.
|
External/permanent storage used for long-term data storage.
|
|
Types
|
RAM (volatile), ROM (non-volatile).
|
Hard disks, SSDs, CDs, DVDs, USB drives, memory cards, etc.
|
|
Volatility
|
Mostly volatile (RAM loses data when power is off).
|
Non-volatile (data is retained even without power).
|
|
Speed
|
Very fast (directly works with CPU).
|
Slower compared to primary memory.
|
|
Capacity
|
Smaller (usually measured in GBs).
|
Much larger (can be in TBs).
|
|
Usage
|
Stores data and instructions currently in use.
|
Stores data, software, and files permanently.
|
|
Direct CPU Access
|
Yes, CPU can directly fetch data from it.
|
No, data must be transferred into primary memory first.
|
Unit of Storage
The Unit of Storage refers to the basic measurement used to
describe the size or capacity of computer memory and storage devices. It tells
us how much data a storage medium can hold.
In other words a unit of storage is a way of measuring how
much information can be stored in memory or on a device,
Common Units of
Storage:
- Bit (b)
→ the smallest unit of data, either
0
or 1.
- Nibble
→ 4 bits.
- Byte (B)
→ 8 bits (enough to store one character, e.g., “A”).
- Kilobyte (KB)
= 1024 Bytes.
- Megabyte (MB)
= 1024 KB.
- Gigabyte (GB)
= 1024 MB.
- Terabyte (TB)
= 1024 GB.
- Petabyte (PB)
= 1024 TB.
- Exabyte (EB)
= 1024 PB.
Conversion from one storage unit to another
We
can convert from one unit of storage to another. This is done through the
following process
- To
go up (KB → MB → GB → TB), divide by 1024.
- To
go down (TB → GB → MB → KB), multiply by 1024.
Example 1: Convert 2048 KB to
MB
Solution
Since we are moving from small unit to large unit, we divide
2048 ÷ 1024 = 2 MB
Example 2:
Convert 3 GB to MB
Solution
Since we are moving from large unit to small unit, we multiply
3 × 1024 = 3072 MB
Example 3 Convert 5 GB to KB
To perform this
conversion, you multiply by 1024 twice, first convert to megabytes from gigabyte
and from megabyte to kilobytes.
The calculation is as follows: 5 GB×1024 MB/GB=5120 MB
5120 MB×1024 KB/MB=5,242,880 KB
Home works
- Convert
8192 KB to MB.
- Convert
5 GB to MB.
- Convert
2 TB to GB.
- Convert
512 MB to GB.
- Convert
1,048,576 KB to GB.
- Convert
4 TB to MB.
- Convert
256 Bytes to Bits.
- Convert
64 GB to TB.
- Convert
131,072 KB to MB.
Comparison of Auxiliary Storage Devices
|
Device
|
Size
/ Portability
|
Memory
Capacity
|
Speed
|
Technology
|
Typical
Use
|
|
Hard
Disk Drive (HDD)
|
Medium, not very portable (internal or external)
|
High (hundreds of GB to several TB)
|
Moderate (mechanical, slower than SSD)
|
Magnetic storage with spinning disks
|
Storing OS, software, and large files
|
|
Solid
State Drive (SSD)
|
Small to medium, portable (internal or external)
|
High (hundreds of GB to several TB)
|
Very fast (uses flash memory, no moving parts)
|
Flash-based electronic storage
|
Faster boot-up, apps, gaming, modern laptops
|
|
Optical
Discs (CD/DVD/Blu-ray)
|
Small, portable
|
Low–Medium (CD ~700 MB, DVD ~4.7–8.5 GB, Blu-ray ~25–50
GB)
|
Slow (requires disc drive)
|
Laser technology (optical storage)
|
Movies, music, software distribution
|
|
USB
Flash Drive (Pen Drive)
|
Very small, highly portable
|
Medium–High (2 GB up to 1 TB)
|
Fast (USB 3.0/3.1 very quick)
|
Flash memory
|
File transfer, backups, portable storage
|
|
Memory
Cards (SD, microSD)
|
Very small, portable
|
Medium (up to 1 TB in modern cards)
|
Fast (depends on class/speed rating)
|
Flash memory
|
Cameras, smartphones, tablets
|
|
Magnetic
Tape
|
Large cartridges, not portable for everyday use
|
Very high (up to multiple TB per tape)
|
Slow (sequential access only)
|
Magnetic tape reels
|
Backup and archival storage for organizations
|
|
|
|
|
|
|
|
A. information processing B. information transmission C. modulation D. synchronization
