3.4 Computer Systems Flashcards
How do you calculate the number or possible inputs?
2^n Where n is the number of inputs
What does an AND gate truth table look like?
A B A AND B
0 0 0
0 1 0
1 0 0
1 1 1
What does a OR gate truth table look like?
A B A OR B
0 0 0
0 1 1
1 0 1
1 1 1
What does a NOT gate truth table look like?
A NOT A
0 1
1 0
What does a XOR gate truth table look like?
A B A XOR B
0 0 0
0 1 1
1 0 1
1 1 0
Symbol for AND
A.B
Symbol for OR
A+B
Symbol for NOT
̅A
(A is meant to be fully under the line)
Symbol for XOR
A⊕B
What is Hardware?
A computers hardware consists of physical parts including external and internal devices (storage devices, CPU, GPU, RAM and more)
What is Software?
The non physical programs that are stored by and run on a computer system
Software makes use of the physical hardware components and devices
Examples of Hardware
Monitor
Motherboard
CPU
GPU
RAM
Examples of Software
Operating system
Drivers
Computer game
Spreadsheet
Web browser
What does an operating system do?
It is the interface between you and the computer
They are responsible for managing: - Processor(s) - Memory - Input/output devices - Applications (Apps) - Security
What is processor management?
Managing the processor
The operating system is responsible for deciding which program will run on the processor an how much time it will get to run
What is multitasking?
Multiple programs running at the same time
Multitasking might be having a web browser, Spotify and discord open at the same time
Many other background processes also are running
What is an interrupt?
Interrupts are signals sent to the CPU by external devices to indicate an event that needs immediate attention.
They tell the CPU to suspend its current activities and execute appropriate instructions
Hardware interrupts are generated by hardware devices (e.g. Printer that has no paper or ink)
Software interrupts are generated by programs (for example, a divide-by-zero error will cause an error message to be displayed)
Memory Management
Where does a program need to be stored when a program is executed?
RAM
To run the program, the computer must copy the program from secondary storage to main memory.
Why does memory management need to be managed by the OS?
The OS will need to keep track of where each program and its data are located
The OS will need to make sure not to overwrite existing programs and data
How does the OS mange input/output devices?
The OS must manage input/output devices including:
-Getting inputs from and sending outputs
to peripheral devices
What is a driver?
-A driver is a program that controls peripheral devices such as printers, mice, simulator kit (i.e. Yoke system for a flight sim) and displays
-Each device communicates to the OS through its own driver
-Many device drivers come with an OS but if you buy a brand new type of device, it will be supplied with a driver, which you will need to install
What is application software?
Software that performs a user-oriented task
What are some examples of application software?
HINT: they are not brand names.
Presentation software
Multimedia software
PDF viewer
Web browser
Email client
How does the OS manage application software?
The OS provides graphical user interface (GUI) features such as windows, maximise, minimise, resize
When an application is run it is allocated space in RAM and is loaded onto the RAM.
When an application is closed it will be removed from RAM.
The OS may also be responsible for updating and installing applications .
What does security management often contain?
- Firewalls and antiviruses
- User management - Login details (username and password)
- Access rights - to files, programs and services: (have you paid?)
- Encryption - of hard drives and removeable media
- Memory protection - prevention of programs being able to view or overwrite data stored in the RAM
Security updates are automatically downloaded and installed
What is Utility Software?
Utility programs perform extra functionality and housekeeping tasks that keep computers running efficiently.
They are often packaged as part of the operating system.
Some utility programs, such as Antivirus software, are bought as stand-alone software programs.
What are some examples of Utility Software?
Encryption software
Defragmentation software
Data compression
Disk clean-up tools
Disk formatters
Anti-virus software
What gets encrypted?
- Encrypt entire Hard disks so that the data cannot be understood if the computer is stolen
- Encrypt files and files on a portable disk such as USB removeable storage
- Encrypt communication with websites
- Encrypt data in an organisation’s database -especially sensitive data such as passwords
What is Disk Defragmentation?
The file is referred to as ‘fragmented’ - It is stored in different locations so that it will take longer for the computer to find.
Read times will become faster, free space is also in one place so new files do not need to be fragmented
BEFORE (Disk is Fragmented)
1 2 8 7 7 5
2 4 6 7 3 3
3 2 1 2
AFTER (Disk is Defragmented)
1 1 2 2 2 2
3 3 3 4 5 6
7 7 7 8
Compression
- Some utilities enable users to compress and decompress files or folders
- This makes the file smaller
- If sending the files, it reduces the amount of data that is sent
- Compression may allow attachments to be sent via email that would otherwise have been larger than a file-size limit
- More data can be stored on backup media
- Lossy / Lossless
Examples of High Level languages
VB.NET
Python
C#
C++
Java
PHP
Example of a Query language
SQL
Examples of Markup languages
HTML
XML
Example of a Low Level language
Assembly Language
What is machine code?
In the first computers, all programs were written in machine code
Instructions were written in binary, so a typical instruction looked like this:
- 101011001001
Machine code is what computers translate assembly code and high level languages into.
What did every machine code instruction do?
Each instruction did one very small task like LOAD the value 1 into the accumulator register