4.1 Types of software and interrupts

# Software
A set of instructions written in a programming language that performs one or more tasks to tell the computer what to do.
## System Software
- provides services that the computer requires , including operating system and utility software
- manages/maintains the hardware/software
set of programs to control and manage the operation of computer hardware
provides a platform on which other software can run
required to allow hardware and software to run without problems
provides a human computer interface (HCI)
controls the allocation and usage of hardware resources.
##### Examples
- Compiler: **Translates** high-level language into machine code, allowing for direct use by a computer to perform tasks without re-compilation.
- Linker: Combines object files produced by a compiler into a single program, allowing the use of separately written code modules in the final program.
- Device driver: Software that enables hardware devices to communicate with a computer's operating system, without which a device like a printer would be unable to work.
- Operating system: Software that manages basic computer functions such as input/output operations, program loading and running, and security management, making computers more user-friendly.
- Utility programs: Software that manages, maintains, and controls computer resources by carrying out specific tasks, such as virus checking, disk repair and analysis, file management, and security.
### Utility Software
- Computer users have access to utility programs as part of system software
- Utility programs can be initiated by the user or run in the background without user input
- Common utility programs include virus checkers, defragmentation software, disk analysis and repair tools, file compression and management software, backup software, security tools, and screensavers.
####  Virus Checkers & Anti-Virus Software
- Virus checkers or anti-virus software are important for protecting computers from malware.
- They should be kept up to date and run in the background to maintain their effectiveness.
- Anti-virus software checks files before they are run or loaded and compares possible viruses against a database of known viruses.
- Heuristic checking is used to identify possible viruses that are not yet on the database.
- Infected files are put into quarantine for automatic deletion or for the user to decide.
- Anti-virus software must be updated as new viruses are constantly discovered.
- Full system scans should be carried out regularly to detect dormant viruses.
#### Disk Defragmentation Software
- Defragmentation software rearranges the data blocks on a hard disk drive (HDD) to store files in contiguous sectors, reducing head movements and improving data access time.
- As an HDD becomes full, blocks used for files become scattered all over the disk surface, making it slower to retrieve data as the HDD read-write head needs several movements to find the data.
- When a file is deleted or extended, new data does not fill the vacant sectors immediately, causing the files to become more scattered throughout the disk surfaces.
- A disk defragmenter rearranges the data blocks to store files in contiguous sectors wherever possible, allowing for faster data access and retrieval.
- The defragmentation process can free up previously occupied sectors and empty some tracks.
#### Backup Software
- Backup software is a utility software that helps create and manage backup copies of data files and programs.
- Manual backups using memory sticks or portable hard drives are good practices, but operating system backup utilities are also recommended.
- Backup utilities allow scheduling backups and only backup files if changes have been made to them.
- There could be three file versions for total security: the current version stored on the internal HDD/SSD, a locally backed-up copy on a portable SSD, and a remote backup on cloud storage.
#### Security Software
- Security software is a utility software that manages access control, user accounts, and links to other utilities such as virus and spyware checkers.
- It also protects network interfaces using firewalls to prevent unauthorized access.
- Security software uses encryption and decryption to ensure intercepted data is unreadable without a decryption key.
- It oversees software updates to verify legitimate sources and prevent malicious software from being installed.
- Access control and user accounts use IDs and passwords to secure user data and prevent unauthorized access.
#### Screensavers
- Screensavers display moving and still images on the monitor screen after computer inactivity.
- They were originally developed to protect CRT monitors from 'phosphor burn'.
- Screensavers are now mostly used for customizing a device and as a part of computer security systems.
- They automatically log out of the user after a certain period of inactivity.
- Some screensavers activate useful background tasks like virus scans and distributed computing applications.
#### Device Drivers
- Device drivers translate data into a format that can be understood by the hardware device they are associated with.
- Without the appropriate device driver, a hardware device cannot work with a computer and may not be recognised by the operating system.
- USB device drivers contain descriptors, which include a vendor ID (VID), product ID (PID) and unique serial number that allow the operating system to identify the device.
- Serial numbers must be unique to avoid confusion if two devices with the same serial number are plugged into a computer simultaneously.

### Operating system
- A type of software that manages the main functions of the computer
- including managing files and managing memory.
#### Purpose of the operating system
- It **performs** the basic functions of a computer
- It **manages** the hardware
- It provides a platform to run software
- It provides a user interface
#### Functions of a typical operating system
- managing files
- handling interrupts
- providing an interface
- managing peripherals and drivers
- managing memory
- managing multitasking
- providing a platform for running applications
- providing system security
- managing user accounts
##### Platform for running applications
- allows application software to run on the computer
- allowing communication between the applications software and the hardware
##### Managing files
- file naming conventions which can be used {i.e. filename.docx (where the extension can be .bat, .htm, .dbf, .txt, .xls, etc.)}
- performing specific tasks (for example, create, open, close, delete, rename,copy, and move)
- maintaining the directory structures
- ensuring access control mechanisms are maintained (for example, access rights to files, password protection, or making files available for editing or locking them)
- ensuring memory allocation for a file by reading it from the HDD/SSD and loading it into memory.
##### Memory management
- To make sure memory is used efficiently
- allocates memory to processes
- Moves data to and from memory/between memory and storage
- prevents two processes accessing the same memory
##### Managing peripherals and drivers
- managing the communication between any input and output devices that are connected to the computer
- allocates data to buffers
- transmits data to hardware
- receives data from hardware
##### Multitasking
managing the process of switching between tasks that are being carrying out
##### System security
proving features such as username and password
##### User accounts
allowing multiple user accounts to be created on a computer
#### Running of Applications
- The computer starts its OS (booting up the computer) through the bootstrap loader.
- The BIOS (Basic Input/Output System) tells the computer the location of the OS in the storage.
- BIOS is often referred to as the firmware
- ![image.png](https://doc.lie.ee:33101/media/202509/85673eb806884adcb61fbe66fa119e7c6637.png)

##### Firmware
- Permanent instructions/software that are programmed into/stored in the ROM.
- Instructions/software that allow hardware to be controlled/managed.
- Instructions/software that provides the operating system with a platform to run on.
##### Purpose of firmware
- Permanently store instructions (in ROM)
- Stores instructions to boot up/start up the computer
- Provides the operating system with a platform to run on Controls/manages/allows communication with hardware
- Store instructions securely (to stop them being easily corrupted)
##### Example
- Bootstrap
- Bootloader
- BIOS
- Operating system (in embedded system)
- Programs (in embedded systems)

## Application software
- A type of software that provides services that the user requires 
- allows the user to perform tasks on the computer

used to perform various applications (apps) on a computer
allows a user to perform specific tasks using the computer’s resources
may be a single program (for example, NotePad) or a suite of programs (for example, Microsoft Office)
user can execute the software as and when they require.
##### Example
word processor, web browser, video-editing software
## Interrupt
- A signal sent from a device / software
- Requests processor time // Processor stops to service interrupt
- Interrupts have different priorities

- Interrupt is given priority and placed in interrupt queue
- Processor finishes current **FE cycle** for program
- Processor checks interrupt priority queue // processor checks for higher priority interrupt than program/process
- If lower priority processor runs next FDE cycle for program/process // if lower priority processor continues with program/process
- (if higher priority) processor **stores** current process/registers on stack
- Checks source of interrupt and calls the appropriate ISR
- ISR handles/resolves interrupt
- If there is another higher priority interrupt (than process) then repeat, (otherwise) processor retrieves content of stack/registers/ previous process (to continue with process from program)
### Purpose of an interrupt
To indicate that something requires the attention of the **processor/OS/CPU**
### Why interrupts are needed
- To identify that the processor's attention is required // to stop the current process/task
- To allow multitasking
- To allow for efficient processing // prioritising actions
- To allow for efficient use of hardware
- To allow time-sensitive requests to be dealt with
- To avoid the need to poll devices
### Buffer
- a memory area that stores data temporarily
### Generate interrupt
- Keyboard
- Key pressed
- Mouse
- Button clicked

Devices that make use of interrupts
- Keyboard
- Printer
- Mouse