Operating Systems

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UNIX - An Inroduction

What is an operating system? · Kernel - provides a well-defined interface between programs and the hardware. It is a resource manager where the resources include memory, CPU access, input/output ports, etc. · Shell - interacts with the user, accepting commands and starting user programs. · Utilities - include programs required to make the system useful, such as programs to copy files, or simple text editors. · Windowing system - a collection of programs that implement a graphical user interface. Although the traditional definition of an operating system includes just the kernel, it is now more commonly known as a collection of most or all of these components. How A Kernel Defines the Operating System How a kernel defines the interface between programs and the underlying hardware greatly affects the programs designed for that operating system. Some features that define the kernel are: · Single or Multi-Tasking · A single-tasking operating system allows only one program to run at a time. This program must complete before a second program may begin. · A multi-tasking operating system allows multiple programs to run on the same system. In order to do this, it must define a means of communicating between programs, protecting running programs from errors encountered in other programs, and for scheduling when programs will run. · Single or Multi-User · A single-user operating system has only one user at a time. This user is granted exclusive access to all system resources. · A multi-user operating system can have more than one user at the same time. Most multi-user operating systems are also multi-tasking. · Memory Management · This defines how memory is allocated to specific tasks, and how memory is protected from other processes. · Device Interface · Device interfaces define the nature of the peripherals which may be connected to a system, the ease with which new devices are added, the extent to which the full power of a device may be used, and how knowledgeable user programs have to be to work with that device. · File System · The design of the file system is often so closely linked to the kernel design that is often the first indicator of differences between similar operating systems. This can include such simple clues as how files are named, or how directories or folders are named. · Degree of Integration · While some systems attem...

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...iles (password, group files) /tmp area for temporary storage, usually cleaned up after reboots, never store important files here Hard Drives, Partitions, CDROM, Network Drives, … · In other operating systems (DOS, Windows, Mac, OS/2) second hard drives, partitions, CDROMS, and network drives are displayed as a separate folder at the same level as the main drive (i.e. C:, D:, E:). · In Unix there is nothing before the root /. All other drives are contained within the root, transparent to the user. The root user sets up the additional drives using the mount command. · /dev/sda1 on / is the main hard drive mounted at the root · /dev/sdb2 on /home2 is a second hard drive mounted at /home2. That is if you look at the contents of /home2 you will be looking at the contents of the second hard drive. · /dev/scd0 on /cdrom is a SCSI cdrom mounted at /cdrom. · fox:/home on /tmp/home is the home directory of the machine fox mounted at /tmp/home.

Bibliography

1. Learning the UNIX Operating System, 4th Edition By Jerry Peek, Grace Todino, and John Strang O’Reilly & Associates, Inc. 2. UNIX For Dummies, 2nd Edition By John R. Levine and Margaret Levine Young IDG Books Worldwide, Inc.

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