It is an interface between hardware and user and according to which different peripherals devices perform their function.It provide environment for program development and execution and performs device management,memory management,resource sharing.
Types of OS:-
- Batched OS
- Distributed OS
- Real time OS
- Timesharing OS
- Multi Programmed OS
Most Popular OS:-
- Windows XP
- Windows Vista
- Windows 7
Architecture of OS:-
- Micro kernel OS
- Macro kernel OS
Micro kernel and Macro kernel OS is divided into 2 parts:-
- Kernel
- User
Kernel is a part where all os services are stored and User is a part where all user related services are stored.A micro kernel is a minimal operating system that performs only the essential functions of an OS.A macro kernel is a operating system that performs all the functions of an os.In Micro Kernel OS ,Kernel occupies more space than the user that is the reason why micro takes more time for booting procedure and in a Macro Kernel OS, Kernel occupies less space than the user and it takes a less time for booting procedure.
OS has many other features like scheduling ,is done to load balance a system effectively or achieve a target quality of service and there is a scheduler which is concerned mainly with:latency ,response time,waiting time.
Throughput -The total no.of processes that complete their execution per time unit.
Response Time- Amount of time it takes from when a request was submitted until the first response is produced.
Latency Time- Turn around time + response time
Waiting Time -Time for which process remain in the ready queue
Types of Schedulers:-
- The long term or admission scheduler decides which job or process are to be admitted to the ready queue.
- The medium term scheduler temporarily removes process from main memory and place them to secondary memory.
In scheduling process starvation is a problem which is a resource management problem where a process does not get a resource for a long time.
Aging is a technique which is used to avoid starvation problem.It works by adding a aging factor to the priority of each request.
Multi Programming is a technique in which several programs are running at a time using timesharing.
Hard Real Time System performs a critical task within a guarnteed amount of time.
Logical Address is generated by CPU and also known as Virtual Address and Physical Address is seen by the memory unit.Paging is a solution for external fragmentation.
Virtual Memory is hardware technique where thes system appears to have more memory that it actually does.
OS Components:-
- Process Management
- File Management
- Main Memory Management
- I/O Management
Cache is a memory which has a more speed than the RAM and a computer processor can access a cache in less time than regular RAM
