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Contents
- Today's Topic: Introduction to Operating Systems
- We will learn
- What is Operating System?
- What OS does?
- Structure of OS
- Evolution of OS Batch Processing, Multiprogramming, Time sharing systems
- Operating System Functions
- Main Funtions of OS
- Types of OS Single User, Multi User systems
Operating Systems
What OS does?
An operating system performs basic tasks such as,
- controlling and allocating memory,
- prioritizing system requests,
- controlling input and output devices,
- facilitating networking and
- managing file systems.
Structure of Operating System:
Application Programs
System Programs
Software (Operating System)
HARDWARE
(Contd…)
Structure of Operating System (Contd…):
3. System programs This layer consists of compilers, Assemblers, linker etc. 4. Application programs This is dependent on users need. Ex. Railway reservation system, Bank database management etc.,
Evolution of OS:
- The evolution of operating systems went through seven major phases.
- Six of them significantly changed the ways in which users accessed computers through the open shop, batch processing, multiprogramming, timesharing, personal computing, and distributed systems.
- In the seventh phase the foundations of concurrent programming were developed and demonstrated in model operating systems. (Contd…)
Evolution of OS (contd..):
Timesharing Simultaneous userinteraction,
On-line file systems
Multics file system (1965), Unix (1974)
Concurrent
Programming
Hierarchical systems, Extensible kernels, Parallel programming concepts, Secure parallel languages
RC 4000 system (1969), 13 Venus system (1972), 14 Boss 2 system (1975).
Personal
Computing
Graphic user interfaces OS 6 (1972) Pilot system (1980)
Distributed
Systems
Remote servers WFS file server (1979) Unix United RPC (1982) 24 Amoeba system (1990)
Batch Processing:
- In Batch processing same type of jobs batch (BATCH- a set of jobs with similar needs) together and execute at a time.
- The OS was simple, its major task was to transfer control from one job to the next.
- The job was submitted to the computer operator in form of punch cards. At some later time the output appeared.
- The OS was always resident in memory. (Ref. Fig. next slide)
- Common Input devices were card readers and tape drives.
Multiprogramming:
- Multiprogramming is a technique to execute number of programs simultaneously by a single processor.
- In Multiprogramming, number of processes reside in main memory at a time.
- The OS picks and begins to executes one of the jobs in the main memory.
- If any I/O wait happened in a process, then CPU switches from that job to another job.
- Hence CPU in not idle at any time.
Multiprogramming (Contd…):
OS
Job 1
Job 2
Job 3
Job 4
Job 5
- Figure dipicts the layout of multiprogramming system.
- The main memory consists of 5 jobs at a time, the CPU executes one by one. Advantages:
- Efficient memory utilization
- Throughput increases
- CPU is never idle, so performance increases.
Operating Systems functions:
- The main functions of operating systems are:
- Program creation
- Program execution
- Input/Output operations
- Error detection
- Resource allocation
- Accounting
- protection
Types of OS:
Operating System can also be classified as,-
- Single User Systems
- Multi User Systems
Multi-User Systems:
- Provides regulated access for a number of users by maintaining a database of known users.
- Refers to computer systems that support two or more simultaneous users.
- Another term for multi-user is time sharing.
- Ex: All mainframes and are multi-user systems.
- Example: Unix
