3.4 Computer Systems
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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 .