Computer Science ( Computer Systems ) Flashcards
1.1 Systems architechure
Explain the Fetch-Decode-Execute
1. Fetch - The memory address is copied from the program counter to the MAR.
2. Fetch - the instruction stored in the MAR is copied to the MDR.
3. Decode - The instruction the MDR is then decoded by the CU
4. Execute - The instruction is then performed
1.1 Systems architechure
Describe the 3 different main components of a CPU
1. The Control Unit
- This is in overally control of the CPU. Its main job is to manage the fetch-decode-executing of instructions
- It controls the flow of data inside the CPU & outside the CPU
2. The Arithmetic Logic Unit ( ALU )
- The ALU does all the calculations
- It performs logic operations such as AND, OR and NOT and binary shifts
- It contains the accumulator register
3. The Cache
- The cache is very fast memory in the CPU. It’s slower than the registers but faster than RAM
- It stores regularly used data so that the CPU can access it quickly, the CPU checks the cache first before the RAM.
- Caches have a very low capacity & are expensive compared to RAM & secondary storage.
- There are different levels of cache, L1, L2 and L3. Higher level = slower but more size
1.1 Systems architechure
Describe the different components of Von Neumann’s architechture
1. Memory Address Register ( MAR )
- holds any memory address about to be used by the CPU. The address might point to data or a CPU instruction.
2. Memory Data Register ( MDR )
- holds the actual data or instruction. This may have bee nfetched from memory, or be waiting to be written to memory
3. Accumulator
- stores intermediate results of calculations in the ALU.
4. Program Counter
- holds the memory address of the next instruction to be executed for each cycle.
1.2 Memory and storage
Describe the features & purposes of;
A) RAM
B) ROM
A) RAM;
- RAM is used as the main memory in a computer. It can be read & written to. RAM is volatile ( meaning it is temporary memory ).
- The main memory is where all data, files & programs are stored while they’re being used.
- When a computer boots up, the os is copied from secondary storage to RAM.
- RAM is slower than CPU cache, but way faster than secondary storage
B) ROM;
- ROM is non-volatile memory, it can only be read, not written to.
- ROM comes on a small factory-made chip built into the motherboard.
- Contains all the instructions a computer need to boot up, called the BIOS.
- As soon as the computer is powered on, the CPU reads the instructions from ROM. this tells the CPU to perform self checks & set up the computer.
- It is possible to update (‘flash’) the BIOS on a ROM chip.
Memory
Describe what Virtual Memory is & how it functions.
1. When the RAM is full, Computers move data that hasn’t been used recently to a location on secondary storage, virtual memory.
- VM may be needed if; too many applications open, or a particularly memory-instensive application is open.
2. If the CPU has to read data from VM, it must move the data back to RAM, This is slow as data transfer rates are much slower on Secondary Storage than RAM.
3. VM can make a computer slow to respond when switching between applications.
1.2 Memory and storage
Describe the different factors that can affect CPU performance.
1. Clock Speed
- This the number of instructions a single processor core can carry out per second.
- The higher the clock speed, the greater number of instructions that can be carried out per second.
- Some CPUs can be overclocked to make them run at a higher clock speed, however, it could make CPU’s overheat.
2. Number of Cores
- Each core in a CPU can process data independently of the rest
- The more cores a CPU has, the more instructions it can carry out at once, so the faster it can process a batch of data.
3. Cache Size
- The cache is data storage inside the CPU that’s much faster than RAM.
- A large cache gives the CPU faster access to more data it needs to process.
1.2 Memory and storage
Describe the function of GPUs
- GPUs are specialised circuits for handling graphics and image processing. They relieve the processing load on the CPU, freeing it do other things.
- Computers have basic GPUs integrated onto the motherboard or the CPU. For better graphics performance, a dedicated GPU is often used.
- Using high-end graphics cards can greatly improve performance in graphics-intensive applications.
1.2 Memory and storage
Describe the features of; Magnetic, Solid State and Optical Storage
1. Magnetic Storage ( HDDs )
- A hard disk drive is made up of a stack of magnetised metal disks that spin thousands of times a second. Data is stored magnetically in small areas on the disk’s circular tracks.
- A moveable arm can access these areas and read or write data.
2. Solid State Storage
- These are storage devices with no moving parts, used for the same purpose as HDDs - for internal/external storage.
3. Optical Storage
- Optical discs are things like CDs, DVDs and Blu-ray discs.
- Optical discs come in 3 forms: read-only, write-once and rewritable.
- Nowadays their use is declining: As internet speeds have increased, streaming and download services have removed the need for optical discs.
1.2 Memory and storage
Evaulate the benefits & drawbacks of:
A) Magnetic storage
B) Solid state storage
C) Optical Storage
A) Magnetic Storage
Benefits
- cheaper than Solid states, higher capacity than Optical & Solid state, longer read/write life than solid states, reliable
Drawbacks
- slower than solid states, noisy due to moving parts, very durable due to moving parts, aren’t very portable
B) Solid State
Benefits
- faster than HDDs, don’t need degramenting, more shock-proof than HDDs, silent, very reliable, very durable, more capacity than optical
Drawbacks
- very expensive, less storage than HDDs
C) Optical Storage
Benefits
- very cheap, portable, don’t be damaged by water or shocks
Drawbacks
- Lowest capacity, very slow read/write speads, poor reliability compared to flash storage devices, easily scratched
1.5 Systems software
State the main functions of the OS.
The main functions of an OS are to:
- Communicate with internal and external hardware via the device drivers
- Provide a user interface, allowing a user to interact with the computer and vice-versa
- Provide a platform for different applications to run.
- Allow the computer to multi-task by controlling memory resources and the CPU
- Deal with file managment and disk management
- Manage system security & user accounts.
1.5 Systems software
Describe how the OS works in;
A) Peripheral management & Drivers
B) User Interfaces
A) Peripheral management
- Every piece of hardware connected to the computer requires a device driver. Drivers act as a ‘translator’ for signals between OS & hardware
- The OS will choose the correct device drivers for the hardware it detects. If a new hardware is connected, the system will install the new matching driver.
- Drivers may be updated automatically by the OS or manually by the user.
B) User Interface
- A User Interface allows the user to interact with a computer system
- GUI systems are designed to be easy for every day users and are optimised for specific input methods.
- A command-line interface is text based, the user enters specific commands to complete tasks.
- For advanced users, command-line interfaces are far more efficient and powerful than a GUI, they can be used to automate processes using scripts.
1.5 Systems software
Describe how the OS works in;
A) File & Disk Management
B) User Accounts
A) File & Disk Management
- The OS is responsible for file management, the organisation of data into a useable structure.
- It deals with the naming, saving, movement, editing & deletion of data.
- The OS manages the hard disk. It splits the physical disk into storage sectors, decides which sectors to write data to, and keeps track of free space on the disk.
B) User Accounts
- The OS is also responsible for User Account Control. User accounts allow different users to be granted access to specific data.
- On most desktop operating systems each user has access to their own personal data and desktop, but cannot access other users’ personal data.
1.5 Systems software
Describe how the OS works in Multi-tasking & Memory management
- When an application is opened, the OS moves the necessary parts of the application to memory. The OS will decide if applications or features have been used recently, if not, they may be removed from memory.
- To run multiple applications, the OS needs to make sure the applications don’t overwrite or interfere with each other. A memory manager allocates certain applications certain memory addresses.
- Only 1 application is processed by the CPU at a time. The OS divides CPU time between open applications and may prioritise certain processes in order for instruction to be exectuted in the most efficient order.
1.2 Memory and storage
A) State what is ment by a character set
B) Describe what; ASCII is, UNICODE is
C) Provide the formula for File size
A) Character sets are collection of characters that a computer recognises from their binary representation.
B1) ASCII
- Each ASCII character is given a 7-bit binary code - this means it can represent a total of 128 different characters.
- An extra bit ( 0 ) is added to the start of the binary code for each ASCII character. This means each ASCII character fits nicely into 1 byte.
- The codes for numbers, uppercase letters and lowercase letters are ordered.
B2) Unicode
- This comes in several different forms & tries to cover every possible letter or symbol that might be written. Unicode uses multiple byes for each character.
- It covers all major languages.
C) File size ( in bits ) = number of bits per character x number of characters
1.2 Memory and storage
Describe:
A) How Images are stored
B) The effects of increasing Colour depth & Resolution
A) Most images you use are bitmap images, they’re made up of lots of tiny dots, called pixels
- The colour of each pixel is represented by a binary code. The number of colours available in an image is related to the number of bits the code has.
B1) Colour depths is the number of bits used for each pixel, given the colour depth yo can work out how many colours can be made; Total number of colours = 2^n ( where n = number of bits per pixel )
B2) Increasing colour depth or resolution will increase the quality of the image but also the file size, shown by the formula; File size ( in bits ) = image resolution x colour depth
- Resolution is the number of pixel in the image.
1.2 Memory and storage
Describe how sound is sampled and stored.
-Sound is recorded by a microphone as an analogue signal. Analogue signals are pieces of continually changing data.
- Analogue signals eed to be converted into digital data so that computers can read and store sound files.
- This is done by analogue to digital converters, which are found in most modern recording devices.
- The process of converting analogue to digital is called sampling.
1.2 Memory and storage
Describe how sample rate, bit depth and duration effect; Quality, Size
- Sample rate is how many samples you take in a second, Bit depth is the number of bits available for each sample. You can calculate the size of a sound file using the formula
- File size ( in bits ) = Sample rate ( in Hz ) x bit depth x length ( in seconds )
- Increasing the sample rate will increase the quality of the playback as it will closer match the recording.
- Increasing the bit depth means the digital file picks up quieter sounds, increasing quality.
1.2 Memory and storage
Describe the main uses of compressing data files
- Smaller files take up less storage space on a device
- Streaming and downloading files form the Internet is quicker as they take up less bandwith
- It allows web pages to load more quickly in web browsers
- Email services normally have restrictions on the size of the attachment you can send - compressing the file allows you to send the same content with a much smaller file size.
What are some Pro’s & Con’s of;
A) Lossy Compression
B) Lossless Compression
A) Lossy ( MP3 { Audio }, AAC { Audio }, JPEG { Image } )
1. Advantages Include;
- Greatly reduced file size, meaning more files can be stored.
- Lossy files take up less bandwidth so can be download & streamed more quickly
- Commonly used, lots of softare can read lossy files
2. Disadvantages Include;
- Lossy compression loses data.
- Lossy compression cannot be used on text files.
- While the quality will be worse, its usally unnoticable
B) Lossesless ( FLAC { Audio }, TIFF { Image }, PNG { Image } )
1. Advantages Include;
- Data is only removed temporarily so there is no reduction in quality.
- Lossess files can be decompressed.
- Lossless compression can be used on text & software files.
2. Disadvantages Include;
- Only a slight reduction in file sizes
1.5 Systems software
List & Explain Some Different Utility Softwares
A) Disk Defragmentation
Reason Needed: Files are stored on hard disk, When files are moved, deleted or change size, lots of small gaps appear in the disk.
- Over time the disk becomes more and more fragmented. This makes the reading & writing speeds much slower.
- Why It’s Needed: Defragmentation re-organises data on the hardrive to put the fragmented files back together.
B) Compression Software
- Compression software reduces the size of files by permanetly or temporarily removing data from them.
- Compressed files take up less disk space & are quicker to download.
C) Encryption Software
- Encryption software scrambles data to prevent 3rd parties from accessing it.
- So stolen data is still secure, as only the intended reader will have the key to read it.
Utility Softwares - Help to maintain,
1.3 Computer networks, connections & protocols
Describe the characteristics of a;
A) LAN
B) WAN
A) LAN
- A LAN covers a small geographical area located on a single site.
- All the hardware for a LAN is owned by the organisation that uses it.
- LANs are either wired or wireless
- Often find LANs in businesses, schools & universities.
B) WAN
- A WAN connects LANs that are in different geographical locations.
- Unlike a LAN, organisations hire infrastructure from teleocommunication companies, who own & manage the WAN, this is because WANs are much more expensive
- WANs may be connected using fibre or copper telephone lines, satellite links or radio links.
1.3 Computer networks, connections & protocols
Describe the different reasons why someone should use a LAN
- Sharing files is easier, network users can access the same files, work collaboratively on them and copy files between machines
- You can share the same hardware ( e.g. printers ) on a LAN.
- The Internet connection can be shared between every device connected to the LAN.
- You can install and update software on all computers at once.
- You can communicate with LAN users cheaply & easily
1.3 Computer networks, connections & protocols
Describe the different factors that can affect the performance of networks
- Bandwith is the amount of data that can be transferred in a given time. Available bandwith is shared between the devices on a network, this may cause congestion and slow the network.
- You can limit the bandwith available to each user to address this.
- Wired connections are generally faster & more reliable than wireless. Fibre optic gives much better performance than copper cables
- Wireless performance depends on signal quality so is affected by the range of the device, so physical obstructions may worsing this quality.
1.3 Computer networks, connections & protocols
Describe the roles of; WAPs and NICs
1. WAP ( Wireless Access Point )
- To set up a WI-FI network, you need a WAP device. The WAP is essentially a switch that allows devices to connect wirelessly.
2. NIC ( Network Interface Controller )
- A NIC is an internal piece of hardware that allows a device to connect to a network. These exist for both wired and wireless connections.
