The System Unit

• The System Unit is the overall structure that houses the

processor, memory, and electronic components of the
computer that are used to process data.

• All input and output devices are connected into the

system unit. The system unit is housed by what is known
as system case or computer case. It holds and protects
most components of a computer.
The System Unit
• The Computer Case contains the framework to
support and enclose internal components of the
computer. It helps to prevent damage from static
electricity. It typically made up of plastic, steel, and
aluminum which are available in a variety of styles.
The size and layout of a case is called a form factor.
• It is also designed to keep internal components
cool by using airflow vents and cooling fans.
• Computer cases are referred to in a number of
ways: Computer chassis, Cabinet, Tower, Box and
Housing.
The System Unit
• Tower (Full, Mid, Mini, Small Factor Form)
• Desktop (Standard, Slimline)
Power Supply
- serve as the source for electricity to the computer. Attached are
vital hardware cables and buses for transferring power to various
components in the computer.
The following are the basic connector you can see in
a power supply:
ATX 24 pin main power connector is the standard motherboard
power connector used in nearly every computer.
SATA 15 pin power supply connector is one of several standard
peripheral power connectors. SATA power connectors only connect
to SATA drives like hard drives and optical drives. SATA power
connectors do not work with older PATA devices.
Molex 4 pin power supply connector is a standard peripheral power
connector. Molex power connectors connect to many different kinds
of internal peripherals including PATA hard drives and optical drives,
some video cards, and even some other devices.
The following are the basic connector you can see in
a power supply:
Floppy drive 4 pin power supply connector is the standard floppy drive power
connector. The floppy power connector, also called a Berg connector or Mini-
Molex connector, is included in even the newest power supplies even though
floppy drives are becoming obsolete.

ATX 4 pin power supply connector is a standard motherboard power connector

used to provide +12 VDC to the processor voltage regulator. This small
connector usually attaches to the motherboard near the CPU.

ATX 6 pin power supply connector is a motherboard power connector used to

provide +12 VDC to the processor voltage regulator but the 4-pin variety is the
more commonly used connector. This small connector usually attaches to the
motherboard near the CPU.
Motherboard
• The motherboard is also known as mainboard, system board,
logic board, or MOBO.
• It holds and allows communication between the crucial
components of the computer such as the CPU and memory.
• It also provides connection for other peripherals. This provides
the path which the processor (CPU) communicates with all the
components of the computer.
There are several components that are attached to the
motherboard. These include:
1. Chip – small piece of semiconducting material, where more
integrated circuits are embedded. They have standard-sized pin
connectors that allows them to be attached to the motherboard.
2. Bus - an electrical path that enables data flow between various
system components.
3. Integrated Circuit (IC) – contains microscopic pathways that carry
electric current. The IC contains millions of elements such as
resistors, capacitators, and transistors. Many different kinds of
chips are located in the motherboard
4. Microprocessor – this is the central processing unit on a chip.
Different variety of chip packages:
1. Dual Inline Package (DIP) – this has two parallel rows of pints
that attach the chip package to the circuit board

2. Pin Grid Array (PGA) – holds a larger number of pins because

the pins are mounted on the surface of the package.
Different variety of chip packages:
3. Flip Chip-PGA (CF-PGA) Package – higher performance PGA
packaging that places the chip on the opposite sides of the pins.

4. Single Edge Contact (SEC) Cartridge – does not use pins but
connects to one of the edges in the motherboard.
Motherboard
The form factor of motherboards pertains to the size and shape of the board.
It also describes the physical layout of the different components and devices
on the motherboard.

Various form factors exist for motherboards:

AT – Advanced Technology
ATX – Advanced Technology Extended
Mini-ATX – Smaller footprint of ATX
Micro-ATX – Smaller footprint of ATX
LPX – Low-profile Extended
NLX – New Low-profile Extended
BTX – Balanced Technology Extended
Motherboard
• The function of the northbridge is primarily a fast path between
the CPU and the video bus and system RAM. While the
southbridge connects with the slow hardware/components of the
system.
• See the photo below (courtesy of Quora) to understand the
function of these bridges:
Central Processing Unit (CPU)
• Commonly known as the CPU or processor, this is the
brain of the computer. It interprets and carries out the
basic instructions to operate a computer.
• It impacts overall computing power and manages most
of the computer operations. The motherboard contains
a socket to hold the processor or CPU. The central
processing unit (CPU), also called the processor or
microprocessor, does most of the processing of data
and instructions for the entire system. Because the CPU
generates heat, a fan and heat sink might be installed
on top to keep it cool.
Central Processing Unit (CPU)
• Nowadays, processors have multiple cores called multi-
core processors. This means that the processor is a
single chips that has two or more separate processors.
In multi-core processors, each of the processors run at
a slower clock speed as compared to a single-core
processor, but this efficient process typically increases
performance.
Central Processing Unit (CPU)
• AMD and Intel are the two most popular brands of
processors in the market nowadays.
• Bundled with the processors are the heat sinks. A heat
sink consists of metal fins that draw heat away from a
component. The fan and heat sink together are called
the processor cooler. The photo below shows a CPU
with a heat sink mounted on the motherboard.
 https://irisxzy.wordpress.com/2016/10/01/cpu-alu-cu-and-
registers/#:~:text=ALU%20operates%20the%20instruction.%20
CU,out%20an%20address%20in%20RAM.
Component of CPU
• Control Unit (CU)
• Arithmetic/Logic Unit (ALU)
• Register

Von Neumann Architecture

 Von Neumann Architecture
• showed how a computer executes instructions
and stores instructions and data in its memory. A
scientist called Von Neumann suggested that a
computer system should be split into two parts: a
processor module and a memory module.
• The processor module is a place where
instructions are executed. It is represented as
Central Processing Unit which includes Control
Unit and Arithmetic/Logic Unit in the diagram.
• The memory module is a place where instructions
and data are stored. It is represented as Memory
unit in the previous diagram. (Dale & John)
Control Unit (CU)
• CU acts like a manager in a computer. CU receives
orders from RAM in the form of instruction and decode
(break) that instruction down into specific commands
for other components inside computer system. It directs
the data flow and the operation of the ALU. (Dale & John)
Arithmetic/Logic Unit (ALU)
• ALU does all mathematical operations (arithmetic) (+/-
/compare) and logical (AND/OR) calculations. Some
computers have two ALUs to process two calculations
simultaneously. That is called dual core technology.
ALUs contain several special storage units called
registers. (Dale & John)
Register
• Register is a small, very fast storage area inside CPU. It is
used to store intermediate values from calculations or
instructions that is needed again immediately.

• For instance, when a ALU is commanded to calculate

A*(B+C), ALU needs to calculate B+C first, then ALU need
to store the result for a moment and use the result to
multiply A. It is faster for ALU to access register than
store the data in memory units.
There are four types of Register:
• MAR (memory address register): store memory that
currently be accessed inside RAM
• MDR/MBR (memory data/buffer register): store data from
memory
• Accumulator (A register): a register store immediate result
from ALU
• Program Counter (PC): store the address of the next
instruction (Dale & John)
Buses
• System bus transfers information between different parts inside
computer system.
• Control bus has two wires, set and enable. When CPU wants to
read from RAM, the enable wire will be opened; when CPU wants
to save information on RAM, CPU will enable the set wire.
• Data bus is a two-way bus carry data commute between CPU and
RAM.
• Address bus is a one-way bus carry addresses from CPU to RAM.
(John)
Video
Random Access Memory (RAM)
• The Random Access Memory or RAM acts as temporary
storage as long as the computer is running.
• The contents of the RAM change as programs are
executed. These are chips that are placed directly on the
motherboard. These RAM consists of switches which are
triggered by changes in electric current.
• is the hardware in a computing device where the
operating system (OS), application programs and data in
current use are kept so they can be quickly reached by the
device's processor. RAM is the main memory in a
computer.
Three basic types of RAM:
• Dynamic RAM (DRAM)
• Static RAM (SRAM)
• Magnetoresistive RAM (MRAM)
1. Dynamic RAM (DRAM)
• This kind of RAM needs to be recharged by the CPU. If not, it
loses its contents. There are many variations of DRAM such as:
• Synchronous DRAM (SDRAM) – faster than DRAM because it is
synchronized to the system clock
• Double Data Rate (DDR) SDRAM – faster than SDRAM because
they transfer data twice for each clock cycle
• DDR2 and DDR3 SDRAM – faster than DDR SDRAM
• Rambus DRAM (RDRAM) – type of DRAM faster than SDRAM that
uses pipelining techniques
2. Static RAM (SRAM)
This kind is faster and more reliable than any form of
DRAM. Unlike the DRAM, this does not need to be re-
energized. However, it is much more expensive and it used
for special purposes.
3. Magnetoresistive RAM (MRAM)
• This kind stores data using magnetic charges instead of electrical
charges. It has greater storage capacity, consume less power, and
faster access times.
Memory module
The RAM chips are housed in a small circuit board called the
memory module, which is inserted into the motherboard.
1. Single Inline Memory Module (SIMM) – this has pins on opposite
sides of the circuit board which connect together to form a single
set of contacts. This houses SDRAM chips along with DIMMs.
2. Dual Inline Memory Module (DIMM) – the pins on the opposite
sides of the circuit board do not connect and form two sets of
contacts. This houses SDRAM chips along with SIMMs.
3. Rambus Inline Memory Module (RIMM) – this houses RDRAM
chips
• The computer will need a certain amount of memory to be able to
handle programs, data, and information, depending on the types of
applications used.
• The more RAM a computer has, the faster the computer will be.
• To be able to use basic application software such as Office Suite, one
needs at least 1GB of RAM.
• Using programs and multimedia should have at least 4GB.
• Playing modern games or using editing software will require at least
8GB.
• Today the RAM ranges up to 64GB depending on the programs that
will be used for the computer.
Read-Only Memory (ROM)
• is a type of computer storage containing non-volatile,
permanent data that, normally, can only be read, not
written to.
• ROM contains the programming that allows a computer to
start up or regenerate each time it is turned on.
• ROM also performs large input/output (I/O) tasks and
protects programs or software instructions.
• Once data is written on a ROM chip, it cannot be
removed.
Read-Only Memory (ROM)
• Almost every computer incorporates a small amount of
ROM that contains the start-up firmware.
• This boot firmware is called the basic input/output system
(BIOS).
• This software consists of code that instructs the boot-up
processes for the computer -- such as loading the
operating system (OS) into the random access memory
(RAM) or running hardware diagnostics. Consequently,
ROM is most often used for firmware updates.