Rapidshare operating systems concepts

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It provides all the required services offered by the operating system. It is a simplistic design which creates a distinct communication layer between the hardware and software.

Microkernel manages all system resources. In this type of kernel, services are implemented in different address space. The user services are stored in user address space, and kernel services are stored under kernel address space.

So, it helps to reduce the size of both the kernel and operating system. Skip to content. What is an Operating System? Real time OS A real time operating system time interval to process and respond to inputs is very small. Distributed Operating System Distributed systems use many processors located in different machines to provide very fast computation to its users.

Mobile OS Mobile operating systems are those OS which is especially that are designed to power smartphones, tablets, and wearables devices. Report a Bug. Previous Prev. Next Continue. Home Testing Expand child menu Expand. SAP Expand child menu Expand. Independently means that each application can perform its task with no concern for what the applications of the other users are doing. Switching from one application to another, of course, slows down each of them and affects the response time seen by the users.

Many of the complexities of modern operating system kernels, which we will examine in this book, are present to minimize the delays enforced on each program and to provide the user with responses that are as fast as possible. A protection mechanism against buggy user programs that could block other applications running in the system.

A protection mechanism against malicious user programs that could interfere with or spy on the activity of other users. An accounting mechanism that limits the amount of resource units assigned to each user. To ensure safe protection mechanisms, operating systems must use the hardware protection associated with the CPU privileged mode. Otherwise, a user program would be able to directly access the system circuitry and overcome the imposed bounds.

Unix is a multiuser system that enforces the hardware protection of system resources. In a multiuser system, each user has a private space on the machine; typically, he owns some quota of the disk space to store files, receives private mail messages, and so on. The operating system must ensure that the private portion of a user space is visible only to its owner. In particular, it must ensure that no user can exploit a system application for the purpose of violating the private space of another user.

Usually only a restricted number of persons are allowed to make use of a computer system. When one of these users starts a working session, the system asks for a login name and a password. If the user does not input a valid pair, the system denies access. To selectively share material with other users, each user is a member of one or more user groups , which are identified by a unique number called a user group ID.

Each file is associated with exactly one group. For example, access can be set so the user owning the file has read and write privileges, the group has read-only privileges, and other users on the system are denied access to the file. Any Unix-like operating system has a special user called root or superuser. The system administrator must log in as root to handle user accounts, perform maintenance tasks such as system backups and program upgrades, and so on.

The root user can do almost everything, because the operating system does not apply the usual protection mechanisms to her. In particular, the root user can access every file on the system and can manipulate every running user program.

All operating systems use one fundamental abstraction: the process. In traditional operating systems, a process executes a single sequence of instructions in an address space ; the address space is the set of memory addresses that the process is allowed to reference. Modern operating systems allow processes with multiple execution flows — that is, multiple sequences of instructions executed in the same address space.

Multiuser systems must enforce an execution environment in which several processes can be active concurrently and contend for system resources, mainly the CPU.

Systems that allow concurrent active processes are said to be multiprogramming or multiprocessing. On uniprocessor systems, just one process can hold the CPU, and hence just one execution flow can progress at a time. In general, the number of CPUs is always restricted, and therefore only a few processes can progress at once.

An operating system component called the scheduler chooses the process that can progress.