Thus the basic functions of an OS are – 1. Process Management – Managing the programs that are running. 2. Memory Management – Managing and rationing the memory between processes and data. 3. Storage Management – Managing the permanent Storage of data on disks or other media 4. I/O Management – Managing the input and output 5. Device / Resource Management – Managing devices and resources and allowing the users to share the resources 6. Security and Protection – Securing the system against possible unauthorized access to data or any other entity.
Protecting the parts of the system against damage. 7. Booting the System and getting it ready to work. 8. Data communications – Providing interface to connect to other computers or allowing others to connect Definition: An operating system is a collection of software that coordinates the working of the different components of the system and gets the user’s job done. The operating system provides the user with all the basic things necessary to do his job. What does an os do?? An Operating System exploits the hardware resources of one or more processors to provide a set of services to system users. * An Operating System also manages secondary memory and input/output devices on behalf of its users. Process Control Block: A data structure by which the system identifies a process. It contains – * Identifier: A unique integer associated with a process * State : A currently executing process is in running state * Priority : Priority level relative to other processes * Program counter : Address of the next instruction of the program to be executed. Memory pointers: pointers to the program code and data associated with the process, and any shared memory blocks * Context data: Data in the registers in the processor during process execution. * I/O status information: outstanding I/O requests, I/O devices allocated to the process, a list of files is use by the process, etc. * Accounting information: amount of processor time, etc. Directry structure of unix: The FreeBSD directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important concept to grasp is that of the root directory, “/”.
This directory is the first one mounted at boot time and it contains the base system necessary to prepare the operating system for multi-user operation. The root directory also contains mount points for other file systems that are mounted during the transition to multi-user operation. A mount point is a directory where additional file systems can be grafted onto a parent file system (usually the root file system). This is further described in Section 3. 5. Standard mount points include /usr, /var, /tmp, /mnt, and /cdrom. These directories are usually referenced to entries in the file /etc/fstab. etc/fstab is a table of various file systems and mount points for reference by the system. Most of the file systems in /etc/fstab are mounted automatically at boot time from the script rc(8)unless they contain the noauto option. Details can be found in Section 3. 6. 1. A complete description of the file system hierarchy is available in hier(7). For now, a brief overview of the most common directories will suffice. Directory| Description| /| Root directory of the file system. | /bin/| User utilities fundamental to both single-user and multi-user environments. /boot/| Programs and configuration files used during operating system bootstrap. | /boot/defaults/| Default bootstrapping configuration files; see loader. conf(5). | /dev/| Device nodes; see intro(4). | /etc/| System configuration files and scripts. | /etc/defaults/| Default system configuration files; see rc(8). | /etc/mail/| Configuration files for mail transport agents such as sendmail(8). | /etc/namedb/| named configuration files; see named(8). | /etc/periodic/| Scripts that are run daily, weekly, and monthly, via cron(8); see periodic(8). | /etc/ppp/| ppp configuration files; ee ppp(8). | /mnt/| Empty directory commonly used by system administrators as a temporary mount point. | /proc/| Process file system; see procfs(5), mount_procfs(8). | /rescue/| Statically linked programs for emergency recovery; see rescue(8). | /root/| Home directory for the root account. | /sbin/| System programs and administration utilities fundamental to both single-user and multi-user environments. | /tmp/| Temporary files. The contents of /tmp are usually NOT preserved across a system reboot. A memory-based file system is often mounted at/tmp.
This can be automated using the tmpmfs-related variables of rc. conf(5) (or with an entry in /etc/fstab; see mdmfs(8)). | /usr/| The majority of user utilities and applications. | /usr/bin/| Common utilities, programming tools, and applications. | /usr/include/| Standard C include files. | /usr/lib/| Archive libraries. | /usr/libdata/| Miscellaneous utility data files. | /usr/libexec/| System daemons & system utilities (executed by other programs). | /usr/local/| Local executables, libraries, etc. Also used as the default destination for the FreeBSD ports framework.
Within /usr/local, the general layout sketched out by hier(7) for /usr should be used. Exceptions are the man directory, which is directly under /usr/local rather than under /usr/local/share, and the ports documentation is in share/doc/port. | /usr/obj/| Architecture-specific target tree produced by building the /usr/src tree. | /usr/ports/| The FreeBSD Ports Collection (optional). | /usr/sbin/| System daemons & system utilities (executed by users). | /usr/share/| Architecture-independent files. | /usr/src/| BSD and/or local source files. | usr/X11R6/| X11R6 distribution executables, libraries, etc (optional). | /var/| Multi-purpose log, temporary, transient, and spool files. A memory-based file system is sometimes mounted at /var. This can be automated using the varmfs-related variables of rc. conf(5) (or with an entry in /etc/fstab; see mdmfs(8)). | /var/log/| Miscellaneous system log files. | /var/mail/| User mailbox files. | /var/spool/| Miscellaneous printer and mail system spooling directories. | /var/tmp/| Temporary files. The files are usually preserved across a system reboot, unless /var is a memory-based file system. /var/yp/| NIS maps. | Functions of an OS: The operating system on your computer has many functions. While you may not be aware of what many of them are or actually do, the operating system helps you navigate your computer more easily and allows you to manage programs and functions with the computer system itself. One function of your operating system is process management. Every program running on a computer – whether it is in the background or the foreground – is a process. Generally, only one process per CPU can run at one time.
However, multiple processes can run through multi-tasking which entails switching processes very quickly. The operating system makes this type of multi-tasking possible. A second function of the operating system is memory management. Computer memory is arranged in a hierarchical manner with the fastest registers first followed by the CPU cache, random access memory, and then disk storage. The operating system’s memory manager coordinates the use of these various types of memory by tracking which one is available, which is to be allocated or de-allocated and how to move data between them.
This activity, usually referred to as virtual memory management, increases the amount of memory available for each process by making the disk storage seem like main memory. Security is an issue that is very important to all computer users. The security function of your operating system is also very important to the programmers. The system will often use an allow/disallow protocol when other systems are trying to access resources on your computer. Still others will require the use of a user name and password to keep your system secure.
Basic Functions of Os. (2017, Sep 13).
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