OS is a program that do the following main function• As an interface between the user with the

complex hardware Imagine what do you need to do to read a data

from a disk without an Operating System• As a resources manager

Manage memory Manage processor Manage processes Manage file Manage devices

1. Organize and monitor its resources continuously.

2. Enforce the policies that determine who gets what, when, and how much.

3. Allocate the resource when it’s appropriate.

4. Deallocate the resource –reclaim it when appropriate.

Organize the memory accordingly e.q whether it’s a fixed partition, dynamic partition, paging or segments

Check the validity of each request for memory space. Allocates a portion for legal request using certain policies.

Sets up a table to keep track of who is using which section of memory.

Finally when the time comes to reclaim the memory, the memory manager deallocates the memory.

Types of Operating Systems (continued)

• Operating systems for computers fall into following five categories:– Batch– Interactive– Real-time– Hybrid– Embedded

• Distinguished by response time and how data is entered into the system

Batch Systems•Program are run in group or batch•Process in serial, one by one•Using punched card or tape (not limited

in present day)•Efficiency measured in throughput -- number of jobs/ given amount of time (e.g. 30 jobs/hour)

Turnarround – in hours or days

Types of Operating System

Interactive Systems ( time-sharing systems)

– Required time-sharing software, which allow each user to interact directly with the computer.

– Give a faster turn-around time and Provides immediate feedback

– Respond time measured in minutes or seconds depending on number of users

Real-Time Systems– Fastest and are used in time-critical

environment– Data must be processed extremely quickly

because the output influence immediate decisions

– Must be 100% responsive 100% of the time. Response time measured in fraction of sec

– Used in space flight, military system, airport traffic control, high-speed aircraft, industrial processes, sophisticated medical equipment etc.

Types of Operating System

Hybrid Systems

– Combination of batch and interactive– User can access the system interactively and

get fast response– Also accepts and runs batch programs in

background when the interactive load is light– Can take advantage of the free time– Most large computer system are hybrid

Types of Operating Systems (continued)

• Embedded Systems:– Computers placed inside other

products to add features and capabilities

– Operating systems with small kernel and flexible functions capabilities will have potential for embedded system

Computer Control Washing Machine