Chap 1

What is an operating system?

It is THE boss of a computing system.
An operating system (OS) is the executive manager of a computing system that manages all hardware and software.
It controls every file, device, section of main memory and nano-second of processing.

There are 4 managers of an OS:

Each manager must work harmoniously with other managers.

Is in charge of the RAM (main memory).
Checks validity of each request. If request is valid, it allocates a portion of memory that is not in use.
De-allocates memory when program finishes execution.
Preserves space in main memory occupied by the OS itself – cannot allow any part of it to be altered accidentally/intentionally.

Determines how to allocate the central processing unit (CPU).
Keeps track of the status of each process. A process is an instance of execution of a program.
Monitors whether the CPU is executing a process or waiting for READ/WRITE command to finish execution.
Handles a process’s transition from one state of execution to another – comparable to a traffic controller.
Reclaims the processor when the job is finished.
Job scheduler:
- Handles jobs as they enter the system.
- High-level portion.
- Accepts/rejects incoming jobs.
Processor scheduler:
- Manages each process within those jobs.
- Decides which process gets the CPU and for how long.

Monitors each device, channel and control unit.
Chooses the most efficient way to allocate all of the system’s devices, printers, terminals, disk drives etc.
Makes the allocation, starts the operation and later deallocates the device.

Keeps track of all files – data file, assemblers, compilers, application programs.
Enforces access policy – system-only, user-only, group-only or general access.
Controls the types of operation a user may perform on a file – read only, read/write.
Allocates resources when file is opened and deallocates resources when file is closed.

The Processor Manager decides how to allocate the CPU.
Keep track of the status of each job, process, threads etc.
Monitor the CPU while handling each process’s transition. Like traffic controller.
Multiple CPU?

Responsible for connecting with every device that’s available on the system.
Choosing the most efficient way to allocate each of these printers, ports, disk drives, and more based on device scheduling policies.
Example?

Keeps track of every file in the system including data files, program files, utilities, compilers, applications etc.
Enforces restrictions on file access control.

Only for OS with networking capability.
Provides convenient way for authorized users to share resources.
This manager must take overall responsibility for every aspect of network connectivity, including the requirements of the available devices as well as files, memory space, CPU capacity, transmission connections & types of encryption (if necessary).

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