Revision; Test 1

The processor is the brains of the computer system; it processes data and carries out instructions. They are measured in Hertz. Typical speeds of a processor are MHz and GHz (a 1GHz processor executes 1 billion instructions per second).

Cores are where instructions are executed. These can be multi-cored; Dual, Quad or 8-Core. Dual cores may execute twice as many instructions per second.

Cache is a very fast and very small amount of memory in the processor, which holds commonly used instructions. 

The performance of the processor can vary depending on these factors:

Cache: increasing cache size will reduce the number of memory to disk transfers.

Clock Speed: doubling speed will double the number of instructions executed per second. 

Cores: increasing the number of cores may increase the number of instructions executed per second.

The Von Neumann architecture describes a system where the CPU runs programs stored in memory.

Main Memory: all data and instructions currently in use are held here, but are lost when computer is turned off.

Memory Address Register: holds any memory addresses about to be used by the CPU.

Memory Data Register: holds the actual data or instructions.

Control Unit: sends control signals between the different components.

Program Counter: holds the memory address of the instruction for each cycle.

Arithmetic Logic Unit: performs arithmetic (+ or -) and logical (AND, OR and NOT) operations.

Accumulator: stores intermediate results of calculations in the ALU.

System busses: a set of parallel wires connecting two or more components.

The three system busses are Data, Address and Control.

Address bus: carries addresses from the processor to main memory; it is one directional.

Data bus: carries data/instructions from main memory to the processor; it is two directional.

Control bus: sends control signals to instruct which data will be travelling to/from memory.

The Fetch-Decode-Execute cycle describes how the CPU carries out instructions.

FETCH:

Copies memory addresses from the program counter to the MAR, then to the MDR. 

DECODE:

The instruction in the MDR is decoded by the Control Unit. The CU may then prepare for the next step.

EXECUTE:

The instruction is performed. 

Memory is an extremely important part of a computer; without memory, a computer wouldn't know what to do.

Random Access Memory: a temporary memory where data and apps are stored. If a computer is turned off, all data is lost. Adding RAM is only required if the current RAM is 100% filled.

Read-Only Memory: memory that cannot be changed by a user. If a computer is turned off data is retained.

EEPROM: Electronically Erasable Programmable Read-Only Memory. Instructions can be erased and replaced. An example could be sim cards.

Volatile: temporary memory that is lost when computer is turned off. RAM is volatile memory.

Non-Volatile: permanent memory that keeps data even when computer is turned off. ROM is non-volatile memory.

Virtual Memory: an area of secondary storage that is used like RAM, but it is much slower.

Flash Memory: type of EEPROM that is often used to store settings.

Hardware is the physical stuff that makes up a computer system, like the CPU, motherboard and monitor.

Software is the applications that a computer system runs, such as an operating system or games.

Firmware: a system with both hardware and software.

Embedded System: a computer system that is made up of firmware that is used for specialised tasks. It does not contain and operating system.

Peripherals are any devices that are not directly connected to the CPU

Inputs are devices that are used to enter data into a computer, like a keyboard or mouse.

Outputs receive data and display it, like a monitor or printer.

I/O Controllers: hardware that connects to the motherboard

I/O Ports: allow communication between the motherboard and I/O device.

Primary Storage: memory areas that the CPU can access quickly; it is built into the system.

Secondary Storage: storage devices that are not constantly acessible by a computer system; without it, software would need to be installed each time we use it.

Types of Secondary Storage:

Optical Storage is a laser light that creates a pattern using marks on a disk. The marks are detected when it is read and is translated into a readable format. 

Low Capacity; Slow; Relatively Portable; Durable; Unreliable; Decent Price

Magnetic Storage is when read/write heads move across disks and change how magnetised a part of the disk is. 

Very High Capacity; Standard Speed; Not Portable; Nondurable; Reliable; Cheap

Solid State Storage is made of microchips, which are switches. The state of the switches determines if a 1 or 0 is stored.

Standard Capacity; Fast; Portable; Durable; Reliable; Expensive

1KB = 1,024 bytes (examiners accept 1,000 bytes)

Text File = 1 byte per character + 10% for overheads

Image = (Number of pixels * Number of bytes per pixel) + 10% for overheads

Sound File = BytesPerSample * SamplesPerSecond * Channels * Duration

An Overhead is a 10% addition to make the estimation more realistic as more than just data is stored, an example such as the title of a file.

Networks allow devices to share information and resources.

LAN

Local Area Network. It covers a small geographical area, located on a single site. LANs require no hardware. Files are easier to share and you can communicate with LAN users cheaply and easily. Accounts are stored centrally so users can log in from any device.

WAN

Wide Area Network. It covers a wide geographical area. WANs require additional hardware, such as satellites, to manage the WAN. The Internet is the biggest WAN.

Client Server networks are made up of a Server and Clients.

• Managed by a server, so all devices are connected as clients.
• Files and software stored centrally on server.
• Clients must send requests to the server asking for data.
• The server stores profiles passwords and access information.
• Easy to track files and install updates/security.
• Expensive to maintain.
• If the server fails, all clients lose access to their work.

Peer-Peer networks don't use servers.

• All devices are equal, connecting directly to each other without a server.
• Files are stored on individual devices and shared with each other.
• They are easy to maintain.
• No dependence on a server, so if one device fails, the whole network isn't lost.
• Security needs to be installed individually.
• They are not reliable and data may be lost if a device fails.
• Devices are prone to slow down when other devices access them.

Packets contain pieces of data that are transferred over a network. Each packet contains the addresses of the sender and receiver, and their IP addresses. 

Packets have a limited time to live and will disappear from the network over time. 

Network Interface Card: allows a computer to connect to a wired network and transfer packets to and from a computer; contains a MAC (Media Access Control) address which is a physical hardware address.

Routers: interconnection devices used on networks to connect devices; they feature a table which has a list of addresses from packets, and then determine which host to send the packet to. 

Switches: if two or more devices place a packet onto a network at the same time, a data collision occurs, so a switch is an interconnection device that helps solve this issue; as a packet arrives, its address is examined and the switch creates a direct connection to that device.

When accessing a webpage, we use a URL (Uniform Resource Location) to access a page.

HTTP: Hypertext Transfer Protocol, which puts packets together on a web browser

WWW: World Wide Web

The DNS has a list of all domain names and their IP addresses which transfers packets to the correct domain name. Without a domain name, the user would have to type in the IP addresses.

IP Address: a unique string of numbers separated by full stops that identifies each computer using the internet protocol to communicate over a network.

In order to let other people see a website, it will need to be placed on a web server, which is known as hosting. A suitable domain name needs to be given, which is unique. Each domain name would have an associated IP address which would need to be registered to the DNS.

Wireless Access Point: allows for wireless devices to connect to a network; includes connections through WiFi and Bluetooth; provides internet access in public places.

Within a LAN it is possible to break the network into virtual networks to allow one group of devices to not see another group of devices on the network. They share the same network hardware but software determines what the different vitrual networks can access and see. They are easier to maintain and machines can be added/removed from a virtual network without having to re-wire.

A Virtual Private Network is a way of adding an extra level of privacy to your online activity by encrypting a device's internet connections, allowing you to surf the web privately and free from hackers.

The cloud is a network of servers that perform different actions, such as running applications or storing data. The benefits of the cloud are that you can increase storage and access files from anywhere in the world.