My distinguished padlet by (PLE) Juan Kaniyampady Joison

1.1 SYSTEM ARCHITECTURE

jjoiso20 — 2025-01-31 14:24:00 UTC

1.2EMMORY AND STORAGE

jjoiso20 — 2025-01-31 14:31:01 UTC

RAM

jjoiso20 — 2025-01-31 14:34:32 UTC

Random Access Memory (RAM) is a used for a temporary store of instructions and data in use by the CPU for currently executing programs. Programs and data are loaded from the hard disk/solid state storage to RAM for processing. RAM is volatile, which means that the contents are lost when the power is turned off. RAM is read and write capable, which means that you can store new data on it and also read data from it.

ROM

jjoiso20 — 2025-01-31 14:37:07 UTC

Read Only Memory (ROM) is a form of memory in a computer system that holds the instructions that are executed when the computer is first turned on, also known as the ‘bootstrap loader’. It is non volatile, which means that the contents remains when the power is turned off. ROM is read only, which means that it can only be read from and the contents are not changed.

The main purpose of ROM that you will need to learn for the exam is that it holds the boot-up program, but it does also have other uses. It can be used to store programs in special cartridges on portable games consoles and embedded systems sometimes hold their main program in ROM.

RAM ROM COMPAIRONSN

jjoiso20 — 2025-01-31 14:38:39 UTC

VIRTUAL MEMORY

jjoiso20 — 2025-01-31 14:39:37 UTC

Virtual memory has a slower access speed for two reasons, one is that the hard drive or other primary storage device (which is where the Virtual Memory is created), has a slower access speed than RAM. Secondly, all data that is in Virtual Memory needs to be loaded into RAM first before it can be processed by the CPU, this page swapping takes time and the whole process takes more time than reading from RAM directly.

CPU FUNCTION

jjoiso20 — 2025-01-31 14:40:26 UTC

The function of the Central Processing Unit is to fetch, decode, and execute instructions.

The program code instructions are stored in the systems RAM. They are fetched, one at a time, and retrieved along the data bus on the computer. The Control Unit decodes the instruction and sends data and signals around the CPU that carry out (or execute) the instruction.

This cycle repeats constantly. Even when the computer system seems to be doing nothing, it is actually running through this cycle, checking the keyboard, refreshing the display etc.

FDE CYCLE

jjoiso20 — 2025-01-31 14:41:13 UTC

The Fetch Cycle

The PC value is copied to the MAR
PC is incremented
The Instruction at the MAR address is read from RAM

The Decode Cycle

The instruction in the MAR is decoded by the CU

The Execute Cycle

The data at the MAR address is read from RAM
The ALU performs any calculations required on the ACC
The value in the MDR is written to the address in the MAR.

CPU COMPONENTS

jjoiso20 — 2025-01-31 14:49:39 UTC

ALU (Arithmetic Logic Unit)
The function of an ALU is to take binary inputs, execute the operation, and create, store, and distribute binary output. ALUs make arithmetic and logical calculations within a computer's CPU.
CU (Control Unit)
A control unit, or CU, is circuitry within a computer's processor that directs operations. It instructs the memory, logic unit, and both output and input devices of the computer on how to respond to the program's instructions.
Cache
It is a hardware or software that is used to store something, usually data, temporarily in a computing environment. It is a small amount of faster, more expensive memory used to improve the performance of recently or frequently accessed data.
Registers
Registers are small amounts of high speed memory. contained within the CPU. They are used by the processor to store small amounts of data that are needed during processing, such as: the address of the next instruction to be executed.

VON NEUMANN ARCHITECTURE COMPONENTS

jjoiso20 — 2025-01-31 14:52:01 UTC

MAR (Memory Address Register)
MDR (Memory Data Register)
Program Counter
Accumulator

Secondary Storage

jjoiso20 — 2025-02-03 13:09:44 UTC

Computers use primary memory such as random access memory (RAM) and cache to hold data that is being processed. However, this type of memory is volatile, which means it loses its contents when the computer is switched off. General purpose computers, such as personal computers and tablets, need to be able to store programs and data for later use.

Why is secondary storage needed?

jjoiso20 — 2025-02-03 13:11:13 UTC

Secondary storage is non-volatile, long-term storage. It is used to keep programs and data indefinitely. Without secondary storage all programs and data would be lost the moment the computer is switched off.

There are many forms of secondary storage and each type of secondary storage device has its own characteristics. Because all devices are different, some are more suited to certain applications than others.

For example, a hard disk drive has a high capacity and reasonable access speed, making it suitable for everyday storage of programs and data. A USB stick is smaller in capacity, but extremely fast and portable, making it suitable for transferring files between computers.

Not all computers require secondary storage. Embedded computers, such as those found in a digital watch or central heating system, do not need to store data when the power is turned off. The instructions needed to run them are stored in ROM and any user data is held in RAM.

Magnetic storage

jjoiso20 — 2025-02-03 13:12:52 UTC

Magnetic devices such as hard disk drives use magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary '1' and a demagnetised section represents a binary '0'. These sections are so tiny that disks can contain terabytes (TB) of data.

As the disk is spinning, a read/write head moves across its surface. To write data, the head magnetises or demagnetises a section of the disk that is spinning under it. To read data, the head makes a note of whether the section is magnetised or not.

Magnetic devices are fairly cheap, high in capacity and durable. However, they are susceptible to damage if dropped. They are also vulnerable to magnetic fields. A strong magnet might possibly erase the data the device holds.

Optical Devices

jjoiso20 — 2025-02-03 13:14:05 UTC

Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into tracks, with each track containing many flat areas and hollows. The flat areas are known as lands and the hollows as pits.

When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam. A sensor looks for the reflected light. Reflected light (lands) represents a binary '1', and no reflection (pits) represents a binary '0'.

Types of optical devices

jjoiso20 — 2025-02-03 13:17:42 UTC

ROM media have data pre-written on them. The data cannot be overwritten. Music, films, software and games are often distributed this way.
R media are blank. An optical device writes data to them by shining a laser onto the disc. The laser burns pits to represent '0's. The media can only be written to once, but read many times. Copies of data are often made using these media.
RW works in a similar way to R, except that the disc can be written to more than once.

Solid State Devices

jjoiso20 — 2025-02-03 13:21:04 UTC

Solid state devices use non-volatile random access memory (RAM) to store data indefinitely. They tend to have much faster access times than other types of device and, because they have no moving parts, are more durable.

Since this type of memory is more expensive, solid state devices tend to be smaller in capacity than other types. For example, a solid-state drive that holds 256 GB might be of a similar cost to a hard disk with one terabyte capacity.

Solid state devices require little power, making them ideal for portable devices where battery life is a big consideration. They are also portable due to their small size and durability.

Features to consider when buying a suitable storage device

jjoiso20 — 2025-02-03 13:24:12 UTC

Cost - what is the cost per gigabyte (GB)?
Capacity - how much data can the medium hold?
Speed of access - how quickly can data be transferred to and from the medium?
Portability - how portable is the medium? Does it need to be portable?
Durability - how robust is the medium, and how robust will it need to be?
Reliability - how resilient and long-lasting is the medium?

Advantages/Disadvantages of storage devices

jjoiso20 — 2025-02-03 13:40:08 UTC

1.3 Networks and Toppoligies

jjoiso20 — 2025-02-05 12:20:33 UTC

Netowrks computer

jjoiso20 — 2025-02-05 12:21:24 UTC

A network is two or more computers (or other electronic devices) that are connected together for the purpose of communication. They are connected by a wired medium such as cables, or by a wireless medium such as Wi-Fi.

A computer or device that is not connected to a network is called a stand-alone.

Benefits of COmputer networks

jjoiso20 — 2025-02-05 12:22:16 UTC

file sharing - users can share files with other users
hardware sharing - users can share hardware, such as a printer
communication - users can communicate via email, chat, or by video
roaming access - users can sign in to any computer on the network and be able to access their files

Benefits of larger networks

jjoiso20 — 2025-02-05 12:24:57 UTC

centralised maintenance and updates - network managers can apply software updates across a network, removing the need for a user to worry about having to do so
centralised security - anti-virus software and firewalls can be implemented across a network, helping to protect user files from risks
user monitoring - network managers can monitor what users do on a network
levels of access - different users can be given different access rights. This gives network managers the ability to generally restrict user access to certain files, while granting permission to specific users

Disadvantages of computer networks

jjoiso20 — 2025-02-05 12:29:36 UTC

cost - additional equipment is needed to allow computers to communicate
management - networks require management by technical staff such as a network manager
spread of malware - viruses and other forms of malware can easily spread across an improperly secured network
hacking - once a device is connected to another device, it is possible that data may be accessed without the device owner's permission