Features:
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Early operating systems
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One program run by one user at a time
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MS-DOS best known O/S
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I/O directed mainly towards keyboard, monitor & disk storage
Benefits:
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Easily used/learned command language
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Run a variety of Software Application packages
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Simple file storage systems
Disadvantages:
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All system resources dedicated to running a single program
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CPU remains idle if slow I/O is being waited on
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Unable to easily swap data between applications
Features:
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Recent operating systems
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Load & run several programs by one user at a time
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O/S2 and Windows95 are best known examples
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I/O still directed mainly towards keyboard, monitor & disk storage
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System of "threads" used to run parts of processes
Benefits:
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Mainly run a Graphical User Interface (GUI) environment
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Run a variety of Software Application packages at the same time
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More complex file storage systems
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System resources are shared thru' time-slicing for programs and
processes that are running
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Each process appears to have the CPU to itself
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Programs are "isolated" - if one fails, others should not
Disadvantages:
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User can run more processes or programs that can make the system seem
very slow
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Operating System must be careful to prevent programs accessing other
program's resources
Features:
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Operating systems are generally quite mature
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Load & run programs for several users at a time
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UNIX, SNA, VMS are best known examples
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Much more complex than Single-User O/S
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O/S has to keep track of many programs at same time
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O/S allocates & schedules use of shared resources
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CPU (could be several in the system)
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Memory available in total and to
each user
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Disk and tape drives (storage
systems)
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Printers & other peripherals
(eg: comms devices)
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O/S provides security for user data
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O/S prevents unauthorised access to system or other users' data files
Benefits:
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Highly secure file storage system
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Can allow up to thousands of users at a time (depending on hardware)
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Rapid responses to each user - each seem to have system to themself
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Programs are "isolated" - if one fails, others should not
Disadvantages:
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CPU can run more processes or programs that can make the system seem
very slow
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Operating System must be careful to prevent programs accessing other
program's resources
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Difficult to learn command language
Features:
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More than one CPU is installed
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Each CPU has its own separate memory, or shares access to a common
internal memory area
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Each CPU can run identical copies of O/S (Symmetric)
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Operating system can assign specific tasks to each CPU (Asymmetric) -
usually only on very large systems
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Network OS may use multiple CPUs
Benefits:
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Provides an increase in overall processing speed and performance
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Failure of one CPU means the O/S transfers workload to other CPUs - this
is called fault tolerance
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Fault Tolerance actually permits disasters as the system can
recover easily (post-recovery)
Disadvantages:
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Programming instructions are often very complex
Modes of Operation of Operating Systems
Each of these different types of O/S allows the
computer to be used in a number of modes: interactive, batch and real-time.
Interactive:
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Serves on-line users via on-line terminals
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POS (Point of Sale terminals)
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Engineering design
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Airline reservation systems
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Banking service systems
Batch:
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Runs large, time-consuming jobs that do not require interactive user
input/output.
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Queued up and run at specific times
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eg: when usage is low
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Less likely to be interrupted or have data loss
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Payroll
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Backups
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File maintenance
Real-Time:
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Able to react immediately to key events and take action
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Often used to control machines
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Automated manufacturing systems
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Aircraft avionics
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Engine management
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Medical equipment
Operating System Sub-Systems
Process
Management:
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A Process is a unit of work in a system
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Monitoring the state of the system
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Selecting jobs to be run by the system
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Manageing threads (portions of processes)
Memory
management:
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A Process must be in main memory (primary storage) to run
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Allocating and de-allocating memory to processes
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Facilitating memory sharing
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Facilitating memory protection
File
(Storage) management:
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Storing details of every file in the system
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Accessing files for program execution
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Accessing files for data retrieval and saving
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Enforcing file security
Device
management:
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Controlling allocation of system resources to peripherals -
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Console (main system monitor)
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Disk drives and other storage
systems (eg: tape)
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Printers
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Terminals
Characteristics of an Operating System
There are a number of characteristics that distinguish
a good operating system from a "not-so-good" one.
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Should be reasonably easy to modify to meet future needs.
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Should process all user programs and utilise system resources in
efficient manner.
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Should treat all users of the system fairly (does not necessarily mean
treat them equally). Users may be granted different levels of access or job
priorities.
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Should degrade predictably and "gracefully".