What are the various standards in UNIX? Discuss various features of UNIX.

Because of the multiple version of UNIX and frequent cross-pollination between variants, many features have diverged in the different version of UNIX. With the increasing popularity of UNIX in the commercial and government sector, came the desire to standardize of UNIX so that a user or developer using UNIX could depend on those features. The institute of Electrical and Electronic Engineers created a series of standards committees to create standards for “An industry-Recognized Operating Systems Interface Standard based on the UNIX Operating System.”The results of two of the committees are important for the general user and developer. The POSIX.1 committee standardizes the C library interface used to write programs for UNIX. In Europe, the X/Open Consortium brings together various UNIX-related standards, including the current attempt at a Common Open System Environment(COSE) specification. X/Open publishes a series of specifications called the X/Open Portability Guide,Currently at version 4.XPG4 is a popular specification in Europe, and many companies in the United States supply version of UNIX that meet XPG. The United States government has specified a series of standards based on XPG and POSIX. Currently FIPS151-2 specifies the open system requirements for purchases.

Various Features of UNIX:

• multi-user more than one user can use the machine at a time supported via terminals (serial or network connection)

• multi-tasking more than one program can be run at a time

• hierarchical directory structure to support the organization and maintenance of files

• portability only the kernel ( <10%) written in assembler tools for program developments wide range of support tools (debuggers, compilers)

Multi-User Operating Systems

A multi-user operating system allows more than one user to share the same computer system at the same time. It does this by time-slicing the computer processor at regular intervals between the various users.

In the above example, there are five users which share the processor hardware and main memory on a time basis.

Multi-Tasking OperatingSystems

Multi-tasking operating systems permit the use of more than one program to run at once. It does this in the same way as a multi-user system, by rapidly switching the processor between the various programs.OS/2 and Windows 95 are examples of multi-tasking single-user operating system. UNIX is an example of a multi-tasking multi-user operating system.

A multi-user system is also a multi-tasking system. This means that a user can run more than one program at once, using key selection to switch between them.Multi-tasking systems support foreground and background tasks. A foreground task is one that the user interacts directly with using the keyboard and screen. A background task is one that runs in the background (itdoes not have access to the keyboard). Background tasks are usually used for printing or backups.The role of the operating system is to keep track of all the programs, allocating resources like disks, memory and printer queues as required.