Types of Software and Interrupts

System Software vs Application Software

System Software

• Provides the services that the computer requires, including operating system and utility software
• It provides a platform on which software can run.
• It is required to allow hardware and software to run without problems
• It provides a human computer interface (HCI)

Application Software

• It is used to perform various applications.
• It allows a user to perform specific tasks.
• It may be a single program or a suite of integrated programs

Utility Software

Virus Checker

• Scans files stored on a computer system for malicious code
• Scans files when they enter the system / memory stick inserted / download etc.
• Sets up a schedule for virus-checking
• Isolates/quarantines/deletes viruses
• Regularly updates the virus definitions

Defragmenter

• Re-organises the disk contents
• Moves split files so they are contiguous
• Creates a larger area of (contiguous) free space
• Reorganises files on a disk to improve efficiency

Automatic Backup

• Can be set up to automatically backup // schedules backups
• Allows the user to decide what is backed up, e.g. all data // all files that have changed since the last backup
• Allows the user to set up an off-site backup
• May encrypt the backup files
• Restores the data if necessary

Device Drivers

• Software that communicates with the operating system, translates data into a format understood by hardware
• Without drivers, devices will not work with a computer
• Modern Operating Systems automatically detect the device and install appropriate drivers

Security Software

• Manages access control and user accounts
• Uses encryption and decryption to ensure any intercepted data is meaningless
• Oversees software updates (makes sure updates come from legitimate sources)

Operating System

What is an Operating System?

• Operating systems allow users to communicate with their computer system.
• Operating system provides an environment where applications can be run

Functions of an Operating System

Managing Files

• Maintains directory structures
• Specifies tasks that can be performed on a file (e.g. open, close, delete, copy, create, move etc.)
• Space allocated to particular files

Provision of an Interface

• Provides facility for user inputting data
• Provides facility for outputting to the user
• Can be command line driven
• Can be with the use of a GUI

Managing Memory

• To make sure memory is used efficiently
• Allocates/deallocates memory to process
• Moves data between memory and storage
• Creates virtual memory
• Makes sure that two processes do not try to access the same memory location

Allows multitasking

• It allows computers to carry out many tasks/processes at a time.

Managing periferals and drivers (Hardware)

• Installation of appropriate driver software
• Controls access to data being sent to/from hardware
• Controls access to hardware/peripherals; sends commands to device

Managing user accounts

• Maintains access rights to users
• Allows more than one user to log onto the system

Environment on which programs can be run

• Allows application software to run on the computer by fetching instructions and executes them

Managing Interrupts

• Interruption of process while running
• Prioritizes processes

CLI vs GUI

CLI (Command Line Interface)

• User uses a keyboard to type in commands/instructions... to choose from a menu, open software, and so on
• Requires a number of exact commands to do a single task

GUI (Graphical User Interface)

• User interacts with the computer using onscreen icons rather than typing commands
• Chooses from menus, opens software, and so on, by clicking on an icon
• Often uses WIMP environment

**How/why hardware, firmware and an operating system are required to run

applications software**

• Applications are run on the operating system
• The operating system is run on the firmware
• The bootloader (firmware) is run on the hardware

Interrupts

What are interrupts?

• Signal from a device that requires attention from the processor
• Causes the processor to temporarily stop until the request is handled

How an interrupt is handled (Interrupt Service Routine --- ISR)

• At the end of the fetch execute cycle for the current instruction...
• Check for interrupt
• If an interrupt flag is set / bit set in interrupt register
• Processor identifies source of interrupt
• All current contents of registers are saved
• PC loaded with address of interrupt service routine (ISR)
• When the ISR completes, the processor restores the register contents
• Processor continues with next F--E--Cycle

Examples of what can cause an interrupt

• An input/output process (for example, a disk drive or printer requiring more data)
• A hardware fault (for example, a paper jam in the printer)
• User interaction (for example, the user presses CTRL+ALT+BREAK)
• Software errors that cause a problem (for example, division by 0)