Section 1 - Components Of A Computer System

Computer - A machine that takes data, processes it and outputs it to complete tasks efficiently.

A computer system consists of hardware and software that work together to complete tasks

• Hardware - The physical components of a computer system (e.g. CPU, printer.)
• Software - The programs or apllications a computer system runs (e.g. OS, word processor.)

There are many types of computer systems:calculators, watches etc. They can be general purpose or dedicated systems.

• General Purpose - Designed to perform many tasks
• Dedicated Systems - Designed for one particular function

Embedded Systems - Computers built into other devices. They monitor and control machinery to get a desired result, they are usually dedicated systems.

Embedded systems are:

• Easier to design
• Cheaper to produce
• Efficient at doing their task

• Power Supply - Supplies power to hardware such as the motherboard and hard drive.
• Case Cooling Fan - Extracts hot air from computer case.
• CPU Heat Sink and Cooling Fan - Keeps the CPU at a steady temperature..
• CPU - The brain of the computer system.
• Graphics Card - Generates computer graphics.
• Motherboard - The main circuit board where the hardware is connected.
• Hard Disk Drive - Internal secondary storage.
• Optical Drive - For read/writing of optical disks.
• RAM sticks - Data storage..

The CPU (Central Processing Unit) processes all the data and instructions that make the computer system work. The CPU has three main parts, the: Control Unit (CU), Arithmetic Logic Unit (ALU) and Cache.

Control Unit

• Its main job is to execute program instructions by following the fetch-decode-execute cycle.
• It also controls the flow of data inside and outside the CPU.

Arithmetic Logic Unit

• It does all the calculations.
• Performs logic operations and binary shifts.

Cache

• Stores regularly used data for the CPU to access quickly when it is needed
• Faster than registers, slower than RAM
• Low capacity. L1 is fast but low capacity. L3 is slow but can hold more

Fetch

• Copy memory adress from PC to MAR.
• An instruction is fetched from the adress in the MAR
• Copy instruction from MAR to MDR.
• Increment PC to point to the adress of the next instruction. If it is not incremented, the CPU would repeat the same instruction.

Decode

• Instruction in MDR is decoded by the CU.
• The CU can then prepare for the next step.

Execute

• The instruction is performed. (e.g. a calculation is done.)
• The cycle is repeated

Memory - Hardware used to store data that a CPU needs access to and it contains the instructions for the CPU to follow.

RAM (Random Access Memory) is used as the main memory in a computer. It can be read and written to and it is volatile.

• Volatile - temporary memory, requires power to retain its data.
• Non-volatile - permanent memory, keeps its contents even without power.

Data, files and memory is stored in RAM while they are being used. When the computer boots up, the OS is copied from secondary storage to RAM. When software, documents and files are opened, they are copied from secondary storage to RAM.

RAM is slower than the cache but faster than secondary storage.

Virtual Memory

Virtual memory is secondary storage where data from the RAM that is not frequently used is moved when the RAM is full. It is used when a memory-intensive application is being used or when too many applications are open at once. If the RAM needs data in virtual memory, it needs to be moved back which is slow as transfer rates are slower in secondary storage than in RAM. This also means a computer can respond slower when switching between or using memory intensive applications in virtual memory as data is constantly moving between secondary storage and RAM.

ROM (Read Only Memory) is non-volatile memory. It can be read but not written to. It comes as a small chip in the motherboard. It contains the BIOS.

BIOS (Basic Input Output System) - The instructions needed for a computer to properly boot up.

The CPU reads instructions from ROM which tell the CPU to perform self-checks, check everything is working and present and to copy the OS into RAM..The BIOS can be updated. The ROM chip uses flash memory which stores data in electrical circuits. Flash memory is also used in USB Sticks and SD cards.

The BIOS is stored in ROM as it is non-volatile memory so the contents are not lost when the compuer isn't  connected to power. The BIOS also needs to stay the same so its stored in read-only memory, it could be altered in RAM.

The OS uses RAM as RAM stores data currently in use and the OS is always in use.

Although the CPU can only read ROM, it is possible to update the BIOS on a ROM chip.

ROM chips use flash memory which works by storing data in electrical circuits by trapping electrons. flash memory is used in SD cards, USB sticks and SSDs.

CPU performance depends on: Clock Speed, Cores and Cache.

Clock Speed

• Clock Speed - The number of instructions a single processor core can carry out per second.
• The higher the clock speed, the more instructions can be carried out per second.
• Some CPU's can be Overclocked (they run at a higher speed than the factory-set rate) which means they can overheat, crash and cause permanent damage. High performance cooling systems are usually needed.

Number of Cores

• Each core independantly processes data
• The more cores there are, the more instructions can be carries out at once so a batch of data can be processed quicker.
• Software needs to be designed to use multicore processing.
• Some steps may depend on others which means cores will have to wait for other cores to finish their job

Cache Size

• A larger cache gives the CPU faster access to more data it needs to process.

CPU's with higher clock speeds, more cores and larger caches will perform better but will be more expensive.

If a computer has little RAM, it can run slow due to the use of virtual memory.The more RAM, the more applications or memory-intensive applications it can smoothly run, making it faster overall. If the computer has plenty of RAM, increasing RAM may not make a difference. RAM can easily be replaced with new RAM sticks.

GPU (Graphics Processing Unit) - Specialised circuits for handling graphics and image processing. They relieve the processing load on the CPU. For better graphics a dedicated GPU is often used, they are good for graphics-intensive applications like games or design software

Primary storage - Memory areas that the CPU can access very quickly. Primary storage has the fastest read/write speeds and is mostly volatile.

Secondary storage - Where all the data is stored when not in use. It is non-volatile.

Tertiary storage - Used for long term data storage like archives and backups.

HDD'S (Hard Disk Drives)

HDD'S are the traditional internal storage in laptops and PC's. It is made up of magnetised metal disks stacked on each other spinning at a rate between 5400 and 15000 rpm (revolutions per minute).

Data is stored magnetically in areas called sectors. Read/write heads on a moving arm are used to access these sectors. Portable HDD's are often used for backing up and transporting large amounts of data. They are long lasting and reliable but can be easily broken.

SSD's (Solid State Drive's)

SSD's are internal storage devices that often use flash memory. They are quicker at booting up and opening programs/files than HDD's.

Hybrid drives exist which use solid state storage for the OS and programs and a hard disk for data.

Portbale SSD's can also be used for backing up and transporting data.

HDD advantages:                                               

• Cheaper                                                             
• Higher capacity                                                       
• Longer read/write life

SDD advantages:

• Faster
• Doesn't need defragmenting
• Shockproof
• Silent (HDD's make noise)                                                                 -

Storage Media - The actual thing that holds data. (e.g. optical disks)

Storage Device - The thing that reads/writes data to media. (e.g. HDD's)

Optical Discs

Optical Discs are things like CD's, DVD's and Blu-Ray discs. They come in 3 forms: Read-only (e.g. CD-ROM,DVD-ROM) , Write-Once (e.g. CD-R, DVD-R) , Rewritable (e.g. CD-RW, DVD-RW)

Their use is declining now, they used to be used for backing up data, streaming and downloading  but they have low capacity, very slow read/write speeds, and poor reliabilty (rewritable discs) but they are cheap, portable, waterproof and shockproof.

Magnetic Tape

Magnetic tape has a much greater storage capacity than HDD's, it also has an extremely low cost per GB. They are suitable for large, frequent back-ups. It comes in a cassette which require a special tape-drive for read/writing. It is very slow when finding specific data but has a fast read/write speed once evrything is in the right place. This is because it is read/written sequentially (read/written to from beginning to end until it is stopped.)

Slowest                                                                Fastest

Optical Disc, Memory Card, Magnetic Tape, HDD, SDD

Priciest                                                               Cheapest

SDD, Memory Card, HDD, Optical Disc, Magnetic Tape

Lowest Capacity                                    Highest Capacity

Optical Disc, Memory Cards, SDD, HDD, Magnetic Tape.

Systems Software - Software designed to run and maintain a computer system.

Main functions of an OS

• Communicate with internal and external hardware via the device drivers

Every piece of hardware connected to a computer needs a device driver. They translate the signals between the hardware and OS. When a computer boots up, the OS chooses the right driver for the hardware, if there is new hardware the OS will install the matching driver. Updates can be installed automatically by the OS or manually to fix bugs, add features or improve performance

• Provide a user interface

A user interface allows the user to interact with a computer system. GUI (Graphics User Interface) is the most common. They are easy for users by making them visual and interactive. GUI's are optimised for specific input methods, in the past they were WIMP (windows, icons, menus and pointers) based but IOS and Android were created for touchscreen devices, using finger gestures like pinching and swiping.

A command-line interface is text-based. the user types commands to complete tasks. They are less resource havey than GUI's. They are more suited to advanced users and are more efficient and powerful, they can be used to automate processes using scripts.

• Provides a platform for different applications to run.
• Allows a computer to multi-task by managing resources.

When a file is opened, the OS moves the necessary parts to memory and removes the rarely used items from memory. If multiple apllications are being run, a memory manager allocates memory addresses so they dont overwrite or interfere with each other. CPU time is divided as only one application can be processed at a time. some processes are prioritise so instructions can be carried out efficiently.

• Handles file and disk management.

Data is stored as files. File extensions (e.g. .jpg, .mp3) tell the computer which software should be used to open the file. The os is responsible for file manangement (the organisation of file into usable hierarchical structure.) It also deals with moving, editing and deleting files. The hard disk is maintained and organised with utility software.

•  Manage system security and user accounts.

OS's can be single-user or multi-user, multi-user gives users simultaneous access. The OS is also responsible for user account control, they allow different users to access specific data. Anti-theft measures can be used to prevent unauthorised access, such as passwords/pins or fingerprint scanners.

Defragmentation Utilities

Files are stored on a hard disk in available spaces. Small gaps appear on the disk when files are moved, deleted or change size. Over time, the disk becomes more and more fragmented, this makes read/writing slower as the the read/write head has to move back and forth across the disk. Defragmenting software reorganises the data so files are together and empty spaces are together. This helps prevent further fragmentation.

As SDD's don't have moving parts and use flash storage, fragmenting doesnt affect their speed, they can access data fast no matter how it is arranged. Defragmenting can actually shorten their life span.

Backup Utilities

Backup - A copy of a computer system files and settings stored externally so it can be recovered if lost. it can be lost due to theft, flood, malware, hardware failure. A backup utility organises regular backups, creates rescue disks and options for full or incremental backups

Full backups - Every file on the system is copied. They use a lot of space and take a long time to create but are quicker to restore from.

Incremental backups - Only files created or edited since the last backup are copies. They use less storage and are created quicker but the last backup and every incremental backup since then needs to be restored.

Compression Software

Compression software reduces the size of files so they take up less disk space. It is used on the internet to make files quicker to download. They need to be extracted before they can be compressed.

Encryption Software

Encryption software scrambles data to stop third-parties from accessing it. It can be decrypted using a special key. It can also be used as a measure of security and can protect from hackers.

Utility Software - Software that helps to configure, optimise or maintain a computer

Open Source Software

The source code is made freely available for users to legally modify to create their own software which can be shared under the same license and terms. (e.g. Mozilla Firefox, VLC Media Player.)

Advantages of open source software:

• It is usually free
• Encourages collaboration, which increases creativity + innovation
• Very reliable and secure as problems are quickly solved by community

Disadvantages of open source software:

• Small projects may not get regular updates so they could be buggy and not secure
• May be limited user documentation
• No warranties if something goes wrong.
• No customer support
• Cannot be hidden from competitors.

Proprietary Software

The source code is a closely guarded secret, only the compiled code is released. Modification, redistribution and copying is restricted. (e.g. Microsoft, Adobe.)

Advantages of proprietary software:

•  Comes with warranties, documentation and customer support
• Well tested and reliable (as companies reputation depends on this)
• Regular fixes and updates
• Cheaper than custom built software

Disadvantages of proprietary software:

• Can be expesive
• May not fit a users needs
• Expired software may not be maintained.