Types of Operating System

what is a distributed operating system?

• Combines processing power of computers across a network for a single job

• the job is split up into several tasks, each of which is run on a separate computer (parallel processing)

• OS controls and coordinates the computers, presenting to them to the user as if they were a single system 

• In online shopping, which uses this type of OS, one server can handle the basket and another can manage search queries 

what is a multi-tasking operating system?

• may run on a standalone pc or laptop 

• Can run many jobs simultaneously, switching between them so each one appears to be the only one running 

• Mobile phones use their own version of multitasking OS, linked to specific hardware 

  • A low level proprietary OS (specific to device/hardware) is used to handle hardware and special features 

  • Main OS handles user interface and running applications 

what is a multi-user operating system?

• Allows multiple users to use computer at the same time 

• Manages permissions and access rights for each user 

• Server's OS handles the requests of multiple people using different computers on the network at the same time 

• time sharing OS

  • a single powerful mainframe or supercomputer is connected to hundreds of terminals all using the mainframe CPU

  • each user gets a slice of processor time

what is an embedded operating system?

• Application programs are stored in ROM 

• Limited amount of RAM so complex memory management system is not required

• User interface is simple and minimal 

• Often use sensors to take input about their surroundings and send output to control devices

• no permanent storage devices to be managed

what is a real time operating system?

• Respond extremely quickly to inputs 

• Cope with many inputs simultaneously 

• Seen in safety-critical environments 

• If hardware fails, OS must have a failsafe to detect immediately and respond appropriately 

• There is hardware redundancy (duplicate hardware components exist in case one fails) 

• Some of the backups are slightly different to account for errors 

what is a virtual machine?

• When software takes on function of the machine 

• The software may execute intermediate code or run an OS within another to emulate different hardware 

what are device drivers?

• A program that provides a software interface to a particular hardware device 

• Enables OS to access hardware functions without knowing hardware details 

• When a printer is first connected to a computer, the user has to install the device driver onto the computer (Sometimes OS does this automatically) 

• Are hardware dependent and specific to OS 

• Communicates with device via system bus  

• When calling program invokes routine in the driver, it issues commands to device 

• Once device sends data back to driver, it may invoke routines in the calling program

what is the BIOS?

• Program stored in EPROM (erasable programmable read only memory) 

• Gets the computer started 

• Initialises and tests the system hardware components and loads the OS from hard disk into RAM 

• Historically used to help I/O devices interact with application software and operating system 

• In more modern computers, it isn't used after loading the OS