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Comp Theory 1 - Mocks - Coggle Diagram
Comp Theory 1 - Mocks
Memory and Storage
Primary Storage
Primary storage stores data in a volatile manner (except for ROM which is non-volatile). These are a relatively small capacity compared to secondary storage. Primary storage has very fast access times compared to secondary storage.
Differences between RAM and ROM:
- RAM stores currently used instructions/data/parts of the OS, it is a volatile data store, RAM's contents can be changed and it is read and write.
- ROM stores the very first instructions to the computer (Bootstrap and BIOS), it is a non-volatile data store and its contents 'cannot be changed' and it is read only.
Virtual memory is within secondary storage (hard disk); when the RAM is full, programs that are not being used by the CPU transferred over the virtual memory. Using the virtual memory makes the computer slower overall; secondary storage has slower access speeds than the RAM.
Secondary Storage
Types of Secondary Storage Devices and Examples:
- Optical - DVD-RW, Blue-Ray, CD-RW
- Magnetic - Hard disk drive, Floppy disks
- Solid State - SSD, Flash memory, USB
Pros and Cons of Each:
- Optical - Pros: Cheap to distribute, low cost per GB, no moving parts. Cons: Low capacity, easily scratched.
- Magnetic - Pros: Large capacity, relatively low cost per GB, high speed data access. Cons: Moving parts so not very portable, not very reliable, can be affected by magnetic fields.
- Solid State - Pros: Reliable, fast access speeds, relatively large capacity, portable. Cons: Relatively high cost per GB, limited read write cycles.
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Data Storage
ASCII is a 7 bit character set (2^7). Extended ASCII is an 8 bit character set. Unicode is a 24 bit character set (2^24) and allows for foreign characters and/or emojis.
Images are represented by coloured pixels; an image's colour depth is defined as the number of bits (and henceforth range of colours) an image can have.
Sound is represented in binary through the continuous sampling of an analogue wave, these samples help create a binary representation of the wave. Sample rate is the amount of samples taken per second (Hz), bit depth is the number of bits used to record each samples and bit rate is the product of these factors.
Compression
Lossless compression reduces the file size, does not cause data to be lost (can return to original) but does not reduce the file size to the same degree as lossy.
Lossy compression is a form of file compression in which file size is massively reduced but the file cannot be returned to its original form (data is lost). In for such things as sound files, this lost data will hardly be noticable.
Systems Architecture
Architecture
The von Neumann Cycle:
- Fetch - Data/instructions are fetched from the CPU.
- Decode - The CU decodes these incoming instructions/data.
- Execute - Instructions are executed.
- Program counter increments by one
- The cycle repeats.
Components of the CPU:
- ALU - Calculations and logical decisions.
- CU - Controls how data moves around the CPU.
- Cache - Fast access to frequently used instructions/data.
- Registers
Registers of the CPU:
- Program Counter - Holds the address of the next instruction to be executed.
- MAR - Holds the address of where data is to be fetched or stored.
- MDR - Holds the data to be fetched from or written to memory.
- Accumulator - Holds the result of calculations.
CPU Performance
Clock speed is defined as the number of instructions that the CPU can execute per second (measured in Hz).
The number of cores affects the amount of instructions that can be executed at once. More cores is not necessarily better, however, as some pieces of software do not many cores.
Cache size determines the amount of frequently used data/instructions that can be stored. It is faster to retrieve data from the cache than from main memory because it is physically closer to the CPU.
Embedded System
Embedded systems are small computers/systems inside of larger computers/systems, they will typically have a designated function/purpose.
Examples of Embedded Systems:
- Central heating systems.
- GPS tracking systems.
- Electronic calculators.
- Fitness trackers.
Computer Networks
Networks and Topologies
Advantages of Networks:
- Allows for sharing of peripherals.
- Sharing of files.
- Software updates and security can be managed on all devices simultaneously.
- Allows for communication.
A LAN covers a small geographical area (under one mile, these networks use internal network hardware.
A WAN covers a large geographical area, these networks use external network hardware.
Disadvantages of Networks:
- Increases risks regarding data security.
- Malware and viruses can be more easily spread between devices.
- If the server fails, connected devices may not work.
- Devices may work more slowly if there is an abundance of network traffic.
Factors affecting network performance:
- Bandwidth - How much data can be sent through a transmission media at once. This is measured in bits per second.
- Number of users: This can slow the network down is there is insufficient bandwidth.
- Transmission media: Wired connections have a higher bandwidth than wireless connections.
- Error rate: The number of packets that fail to be transferred so have to be sent again. This can depend on environmental factors, the grade of material used in transmission media and cable length.
- Latency: The delay from transmitting media to receiving it; caused by bottlenecks in the network's infrastructure.
Client Server:
- Advantages: Easier to install software updates onto all devices, easier to manage backups, easier to manage security files.
- Disadvantages: Can be expensive to set up and maintain, specialist staff may be required, server is a single point of failure.
A client server model contains a server that controls access and security to a shared file store. It manages access to the internet and provides email services. In this model, users request data and connections from a central server.
A peer-to-peer model contains individual computer that are responsible for their own security, backup and serving their own files to each other.
Peer to Peer:
- Advantages: Easy to maintain, specialist staff not needed, cheaper to set up.
- Disadvantages: Network is less secure, users need to manage their own backups.
LAN Hardware:
- NIC - Connects a device to a wired or wireless network.
- WAP - Allows wireless devices to access the network.
- Switch - Routes packets/data on a LAN.
- Router - Sends data between networks (between LAN's). Uses an IP address to route traffic.
The function of domain name servers is to translate between URLs and IP addresses; if the DNS does not know the corresponding IP address, it will send a request to a higher-up DNS server.
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The cloud provides an additional data store that can be accessed over the internet. Advantages include: access anytime/anywhere, access from any device, large storage capacity, automatic backup.
Disadvantages of the cloud include: an internet connection is necessary, there is no guarantee that data is not being accessed by someone else.
Star topology: All devices connected to a central switch, switch is a single point of failure, if the connection with one device is broken the others are unaffected.
Mesh topology: Every device is connected to every other device, a lot more cabling required.
Wired and Wireless Networks, Protocols and Layers
With twisted pair cables, sending and receiving data at the same time is possible.
Wireless Networks:
- Advantages - Users can move around, new nodes are easily added.
- Disadvantages - Limited range, can be blocked by walls and such, radio signals can be intercepted.
Wired Networks:
- Advantages - Generally a faster rate of data transfer, less likely to experience interference.
- Disadvantages - Expensive to install, users are limited in their movement.
Every device on a network has a NIC, each NIC has a designated MAC address. This is used to route frames on a LAN. MAC addresses are written in hex.
IP addressing is used to route packets on a WAN, it is written in IPv4 and IPv6. An IP address contains a network and a host component.
Standards allow software and hardware to be compatible with devices produced by different manufacturers.
A protocol governs communication between devices on a network. Examples include:
- TCP/IP - Allows for communication within LANs and WANs.
- HTTP/HTTPS - Allows for the sending or receiving of requests for HTML web pages.
- FTP - Used for sending files between devices on a network (typically a WAN).
- SMTP - Governs the sending of emails from a user to a mail server.
- POP - Retrieves emails from a mail server.
- IMAP - Newer version of POP.
A layer is a division of network functionality. Using layers is advantageous as this:
- Allows for complex tasks to be divided into smaller, simpler tasks.
- Allows for devices to be manufactured to work on a singular layer.
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System Software
Operating Systems
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A user interface allows a user to interact with the operating system and application software in a friendly and comfortable manner.
Multitasking is where you have more than one program open and running at one time; this is done through the processor allocating small amounts of time to each program and switches between them.
In order to achieve multitasking, the operating system has to manage the memory; this process can lead to memory becoming fragmented.
Device drivers allow for instructions from the OS to be translated and understood by the piece of hardware.
User management allows for more than one user to have allocated settings and access rights to files and programs on a single device.
File management allows the operating system to present files in a logical order and allows users to rename, delete, copy and move files. An extension to the file name informs the OS what application the file needs to be run on.