Cs 101 ( Module 51-60)

The kernel is the internal part of an operating system that performs basic functions required by the computer installation.
The kernel contains software components such as:
- File manager: coordinates the use of mass storage facilities, maintains records of files stored, and allows files to be grouped into directories.
- Device drivers: communicate with controllers or peripheral devices to carry out operations, and translate generic requests into technical steps.
- Memory manager: coordinates the machine's use of main memory, assigns memory space, and ensures that each program's actions are restricted to its allotted space.

The boot strap process (booting) is performed by a computer each time it is turned on, transferring the operating system from mass storage to main memory.
The CPU expects to find the beginning of the program to be executed at a predetermined address, but the main memory is volatile, losing its contents when the computer is turned off.
To resolve this, a small portion of main memory is constructed from nonvolatile memory cells (ROM), which stores a program called the boot loader.
The boot loader directs the CPU to transfer the operating system from mass storage to main memory, and then executes a jump instruction to that area of memory.

A program is a static set of instructions, while a process is the activity of executing a program under the control of the operating system.
Associated with a process is its current status, called the process state, which includes the value of the program counter, values in CPU registers, and values in associated memory cells.
The scheduler and dispatcher within the operating system's kernel coordinate the execution of processes, maintaining a record of processes, introducing new processes, and removing completed processes.
The scheduler maintains a process table, containing information such as memory area assigned, priority, and whether the process is ready or waiting.

In a time-sharing/multitasking system, the dispatcher oversees the execution of scheduled processes by dividing time into short segments (time slices) and switching the CPU's attention among processes.
The procedure of changing from one process to another is called a process switch (or context switch).
When the dispatcher awards a time slice to a process, it initiates a timer circuit that generates an interrupt signal when the slice is completed.

An important task of an operating system is the allocation of machine resources to processes, including peripheral devices and features within the machine.
Resource allocation appears simple but can lead to malfunctions in a poorly designed system.
Issues arise when two processes demand the same resource at the same time, or when a process is utilizing one resource and waiting for another, leading to a deadlock.

Semaphores are used to control access to shared resources, such as a printer, in a time-sharing/multitasking operating system.
A flag is used to keep track of whether the printer is allocated, with a clear flag indicating availability and a set flag indicating allocation.
However, this simple flag system has a problem, as the task of testing and setting the flag may be interrupted, leading to multiple processes accessing the same resource.### Mutual Exclusion and Semaphores
A semaphore is a flag that prevents multiple processes from accessing a critical region at the same time
A critical region is a sequence of instructions that should be executed by only one process at a time
Mutual exclusion is the requirement that only one process at a time be allowed to execute a critical region
A semaphore is used to guard a critical region, ensuring that only one process can enter the region at a time
A process must find the semaphore clear and set it before entering the critical region, then clear the semaphore when exiting

Deadlock is a condition in which two or more processes are blocked from progressing because each is waiting for a resource that is allocated to another
Three conditions must be satisfied for deadlock to occur:
- Competition for non-sharable resources
- Resources are requested on a partial basis
- Once a resource has been allocated, it cannot be forcibly retrieved
Deadlock can be removed by attacking any one of the three conditions
Techniques that attack the third condition are known as deadlock detection and correction schemes
Techniques that attack the first two conditions are known as deadlock avoidance schemes

An account is a record within the operating system containing user information, such as name, password, and privileges
The operating system uses account information to control access to the system during the login procedure
The administrator (or super user) has highly privileged access to the operating system and can perform maintenance activities

Auditing software records and analyzes activities within the computer system to detect destructive behavior
Auditing software can expose attempts to login using incorrect passwords and identify activities that do not conform to a user's past behavior
Sniffing software is a type of software that records activities and reports them to a would-be intruder
Carelessness of users is a major obstacle to computer security, including selecting easily guessed passwords and sharing passwords with others

Once an intruder gains access to a computer system, they can explore and look for places to insert destructive software
Gaining access to the administrator's account provides the highest level of access and control
If access is gained through a general user's account, the intruder must trick the operating system into allowing access beyond the user's privileges