1. Component 01 – Computer systems
Year 10 Computer Science

2. what is a computer system?
A computer system consists of many components:
Input and output devices
Main memory
Secondary storage devices
the CPU (central processing unit)
The components all cooperate to form a working system, in the same way that different parts of our body work together; you should be able to see the similarities:
eyes and hands, memory, a notebook and the brain!

3. How does a computer system work
The computer system uses a microprocessor.
The microprocessor is responsible for executing the instructions given to it in a program.
It follows the instructions in order to do something useful.
The microprocessor relies on other devices
To allow users to input the instructions
To store the instructions
To transfer the instructions to it so that it can carry them out
To carry out the commands it issues e.g. to print an essay or display an image

4. Similarities to human body
The microprocessor is often called the ‘brain’ of a computer because:
It is where data is processed
Decisions are made
Actions are initiated.
However the brain cannot function independently. It needs things like:
Sensors, e.g. Eyes and ears, to provide it with data
Memory, to store data and information
Muscles, to carry out the actions it decides are necessary
Bundles of nerves to transmit messages to and from the muscles and sensors

5. Similarities to human body
In a similar way, the microprocessor needs other components:
Input devices such as keyboards, mice and light sensors to provide it with data
Memory to store the instructions and the results of its processing
Permanent, long-term memory devices such as hard disk drives
Output devices like monitors, printers and motors to carry out the results of its processing
Bundles of wires, called buses, through which data is transmitted from one component to another.

6. Input, Process, Storage, Output

7. Understanding Input, Process, Storage, Output in daily systems
System: A washing machine
Input
What is the method of
input
Process
What processing is the
System doing?
Storage
What type of information
might the storage hold
Output
What us the end result
Pressing a button on the machine.
The system processes the selection using a pre-determined programs to choose the right setting.
The washing machine stores all the programs required for the washing machine.
The washing machine runs the cycle and washes the clothes.

8. Importance of Computers
General Purpose System
Dedicated Systems
Control Systems
Embedded Systems
Expert Systems

9. Embedded Systems
An embedded system is a computer system built within a larger device such as:
The computer systems in these devices have been built for a range of specific tasks.
Embedded devices are limited to a certain number of tasks.
All of the components in an embedded system including microprocessor, memory and input and output interfaces are on a single printed circuit board.
The memory contains the program.
The board is a component built into a larger device, hence the name ‘embedded’.

10. Remember A computer is a machine that can be programmed.
All computers contain a microprocessor.
A computer system consists of hardware and software.
An embedded system is built into a larger device and carries out a limited number of functions

11. CPU

12. Von Neumann Architecture
The Von Neumann architecture describes a system where the CPU runs programs stored in the memory.
Programs consist of instructions and data which are stored in memory addresses

14. Von Neumann Architecture
PC = Program Counter holds the memory ADDRESS of the instruction for each cycle
The Accumulator stores intermediate results of calculations in the ALU
The Memory Address Register (MAR) holds the memory ADDRESS about to be used by the CPU. The address might point to DATA or CPU INSTRUCTION
The memory data register (MDR) holds the actual DATA and INSTRUCTION. This may have been fetched from memory, or be waiting to be written to memory.

15. Difference to Harvard method
Von Neumann uses one memory for data
Harvard uses separate memory for each

17. Answers Control Unit = Program Counter (PC) ALU = (Accumulator)
Registers = MAR MDR
A False
B True
C False
D True

19. Answers 2a Any two functions e.g. The CU executes instructions
It follows the fetch decode execute cycle
It controls the flow of data within the CPU
It controls the flow of data between the CPU and other parts of the computer system (memory, input and output devices)
2b The ALU carries out arithmetic operations e.g. addition, subtraction and multiplication
It performs logic operations on binary data such as AND OR NOT

20. Answers
2c The Cache memory is extremely fast memory in the CPU. It stores regularly used data and instructions. The CPU can access data stored in the cache much faster than retrieving it from the RAM

21. CPU
The diagram below shows how this is put together.

22. Fetch-Decode-Execute Cycle
The way in which the ‘von Neumann architecture’s set out to execute the program instructions is through the fetch-decode- execute cycle

23. Fetch Stage
In the fetch part of the cycle, instructions and data are moved from the random access memory to the central processing unit.

24. Decode and Execute
In the decode part of the cycle, the control unit interprets the instructions and decides what action to perform. During the execute phase, these instructions are carried out.

25. ROM Vs RAM Random access memory (RAM) Way to think of it:
If you are making a meal, you don't want to have to go all the way to the shop every time you need each new ingredient.
Instead you buy all the ingredients and put them in the fridge; it's much quicker to go there than to the supermarket!
It's the same for computers.
It can take a long time to fetch data and program instructions from the hard drive.
Therefore they are stored in the random access memory (RAM), a temporary store of data, so that information can be retrieved quickly by the CPU when required for the program it is running.’

26. ROM Vs RAM
Memory can be thought of as consisting of billions of pigeon-holes or storage locations.
Each one can hold a byte of data and each one has an address so that the CPU knows where to store and retrieve the instructions and data.
RAM is said to be ‘random access’ because each memory location can be accessed in any order if the ‘address’ of that location is specified.
This speeds up data retrieval as the CPU can go to any location and does not have to start each time at the first location and go through them in order until it finds the correct one.
That method is called ‘serial access’.
RAM is said to be volatile because if there is no electrical power then the RAM will lose all of its data.

27. Difference between ROM and RAM
Video 1
Video 2

28. CPU performance
Everybody wants to have a fast computer that runs multiple programs at the same time, as society we are impatient.
Developers are continually refining computers to tackle this issue.
There are four key factors about CPU architecture that affect its performance:
Clock speed
Number of Cores
Cache Size

29. Clock Speed
This is the number of instructions a single processor core can carry out per second (Hz). For most desktop computers, this will be somewhere around 3.5 billion instructions per second).
The higher the clock speed, the greater the number of instructions that can be carried out per second.
Some CPUs can be overclocked to make them run at a higher clock speed than the factory-set rate. But it’s risky if not done properly – it can make CPUs overheat, causing crashes or permanent damage to the system. Water cooling systems are needed when overclocking.

30. Number of Cores
Each core in a CPU can process data independently of the rest – multi task!
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.
Most PCs and smartphones have 4 or more cores these days.
Q: A new business would like to get a new computer that works quicker.
Using the information above discuss the considerations that need to be made about cores in a computer. (6 marks)

31. Cache size
The cache is data storage inside the CPU that’s much faster the RAM.
A larger cache gives the CPU faster access to more data it needs to process
Generally speaking , CPUs with higher clock speeds, more cores or larger caches will have better performance, but will be more expensive.

32. Cache Memory
Cache is a small amount of memory which is a part of the CPU - closer to the CPU than RAM.
It is used to temporarily hold instructions and data that the CPU is likely to reuse.
The CPU control unit automatically checks cache for instructions before requesting data from RAM.
This saves fetching the instructions and data repeatedly from RAM – a relatively slow process which might otherwise keep the CPU waiting.
Transfers to and from cache take less time than transfers to and from RAM.
The more cache there is, the more data can be stored closer to the CPU.

33. Cache Memory
Cache is graded as Level 1 (L1), Level 2 (L2) and Level 3 (L3):
L1 is usually part of the CPU chip itself and is both the smallest and the fastest to access.
Its size is often restricted to between 8 KB and 64 KB.
L2 and L3 caches are bigger than L1.
They are extra caches built between the CPU and the RAM. Sometimes L2 is built into the CPU with L1. L2 and L3 caches take slightly longer to access than L1. The more L2 and L3 memory available, the faster a computer can run.
Not a lot of physical space is allocated for cache. There is more space for RAM, which is usually larger and less expensive.
Each CPU core has its own L1 cache, but may share L2 and L3 caches.

34. Virtual Memory
Secondary storage used as extra RAM (Random Access Memory)
VM is needed if too many applications are running at once.
The process:
Computers have a limited amount of RAM
As an application is opened, RAM fills up with data.
When the ram is full the computer needed a place to store data, so it moves the data to secondary storage (Virtual Memory)

35. Q1: Explain how virtual memory works
If the CPU has to read data stored in the VM, it must move the data back to RAM to do so; a very slow process.
Using VM can make the computer very slow to respond when moving between applications.
Q1: Explain how virtual memory works
(2 marks)

36. Tiers of Storage
There are 3 main tiers to storage:
Primary Storage
Mostly volatile.
CPU Registers, Cache, ROM and RAM: Quick Data Recovery.
Secondary Storage
Non volatile.
Where data is stored when computer not in use.
Magnetic, Solid State and Optical
Slower than primary
Tertiary Storage
Non volatile
Long term storage: archiving and whole network backups.
Q2: Explain the differences between primary and secondary storage tiers (4 marks)

37. The Operating System
Systems software is software designed to run and maintain a computer system. By far the most important one is the operating system (OS).l There’s also utility software.
Operating Systems manage hardware and run software
An OS is a complex piece of software found on most computer systems.
The main functions of the OS are to:
Communicate with internal and 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 management and disk management

38. Device drivers let the OS and Hardware Talk to Each Other
Operating systems use device driver software to communicate with internal hardware or peripherals connected to the computer system:
Every piece of hardware connected to the computer system requires a device driver.
Drivers act as a translator for the signals between the OS and the hardware.
When a computer is booted up, the OS will choose the correct device drivers for the hardware it detects. If new hardware is connected to the computer, the system will install the new, matching driver.
Device manufactures may release updates to device drivers in order to fix bugs, add features or improve the performance of their hardware. Updates may need to be installed automatically by the OS or manually by the user.

39. Operating Systems provide a user interface
A user interface allows a user to interact with a computer system
Graphical user interfaces (GUIs) are the most common type.
GUIs systems are optimised for specific input methods. In the past, GUIs have been WIMP based (using Windows, icons, menus and pointers). Android and IOS were created for touch screen devices – using finger gestures, pinching and swiping in place of the mouse.
A command line interface is text based. The user enters specific commands to complete tasks. These are used by advanced users.
The OS is the boss of the computer system, gives you a way to interact with the computer, controls hardware via drivers. Allows the computer to run applications and multi task

40. The OS allows Multi-Tasking by managing Resources
Operating systems provide a platform to run applications (by configuring hardware so they can use it, and giving access to the CPU and memory).
Operating systems that can run multiple applications at the same time are called multi-tasking OSs.
The OS helps the CPU carry out multi-tasking by efficiently managing memory and CPU processing time:
When an application is opened, the OS moves the necessary parts of the application to memory, followed by additional parts when they re required. 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 that the applications don’t overwrite or interfere with each other. A memory manager allocates certain applications certain memory addresses, to make sure their processes are placed into separate locations.
Only one application is processed by the CPU at a time, so the other processes must wait. The OS divides CPU time between open applications and may prioritise certain processes in order for instructions to be executed in the most efficient order.
When required, the OS organises the movement of data to-and-from virtual memory.

41. OS deal with User Accounts
OSs can be single user or multi-user. Single user Oss (such as Windows 10 and OS X) allow one user to use the computer at once, whereas multi-user Oss (e.g. UNIX server) allow several users to use the computer at the same time. Multi user Oss are often used on mainframes (huge supercomputers) and give many users simultaneous access. E.g. example ATMs allow thousands of people access to a large bank’s mainframe at the same time.
The OS is also responsible for user account control. User accounts allow different users to be granted access to specific data or resources on a computer system.
On most desktop operating systems each user has access to their own personal data and desktop, but cannot access other users personal data.
Operating systems may have anti-theft measures to prevent other users from accessing locked devices or accounts to steal information. User accounts may be password, or pin protected. Some devices also require a user to draw a specific pattern on the screen, or have fingerprint or retina scanners.
Make sure you know the difference between multi-user and single user operating systems. A single user OS may have multiple user accounts, but only a single person can use the computer at any
one time.

42. Defragmentation
Defragmentation software recognises these issues on the hard drive and puts them back together
It also moves files accordingly to create free space; hoping to prevent fragmentation happen again.
SSDs (Solid State Disk Drives) don’t encounter this issue due to it having no moving parts.

43. How Defragmentation works??
Data on a HDD
Each white space identifies a gap on the HDD.
Notice how organised it is.
Each colour is a file

44. How Defragmentation works??
Data DELETED on a HDD
As files are deleted more gaps start to appear but there is less organisation of those gaps

45. How Defragmentation works??
A new file is add on a HDD
A new file
As new files are added, they take up the spaces that they require.
Sometimes this can lead to files being spread around, causing a slow opening of that file in the future

46. How Defragmentation works??
After Defragmentation
Gaps collected together
All files are organised together neatly.
The new file has been reassembled to ensure it is together.

47. BACKUP UTILITIES: Why??
Backup Utilities software is used to back up data.
It backs up the systems files and settings externally
This means data can be recovered in the event of data loss, such as:
Fire
Theft
Flood
Malware
Hardware Failure

48. BACKUP UTILITIES Back up utility is software with facilities such as:
Scheduling of back ups
Creating rescue disks
Creating disk images
Options for full or incremental back ups to take place

49. Full vs Incremental Full Backup Incremental Backup
A copy of every file on the system is taken.
Use lots of storage.
Time consuming.
Faster to restore
Only files created or edited from the last back up.
Uses less storage space.
Much quicker to perform.
A full system restore will be slow:
The last full back up first
Then, every incremental since

50. Other Types of Utility Software
Compression Software
Encryption Software
Reduces the size of files to take up less space.
Used frequently on the internet.
Commonly used make moving files with large capacity (upload/download)
File formats such as .zip/.rar.
Files are extracted from the zip file to allow them to be used.
Encryption software scrambles data.
This stops unauthorised users getting access.
To get the information from the encrypted file a special key is required.

51. Open Source FREE!!! Propriety Source PAID FOR!! In basic terms… Video
Understanding the basic knowledge of these two types of software is important BUT not enough for the exam!!
FREE!!!
Propriety Source
Video
PAID FOR!!

52. Open Source Software: Overview
Source code is made freely available
Source code is the actual programming code behind the software.
It shows exactly how the software was made.
Examples
Apache HTTP Server (runs webservers)
GIMP (image editing)
Mozilla Firefox (web browser)
Android is another open source software
link 1
link 2

53. Open Source Software Support
Because the source code is freely available there is a big support network for the different types of software.
Online forums – Sharing idea and solving problems.
Users of open source actively help to improve the running of the software