Harold Tabinas

Wednesday, December 6, 2006
11:29 PM

Assignment #3

UNIX Command Summary
There are MANY commands available for you in a UNIX shell account. A list of them follows (in no particular order). Remember, you can always read the manpage on each command for more information.ls ................. show directory, in alphabetical order
logout ............. logs off system
mkdir .............. make a directory
rmdir .............. remove directory (rm -r to delete folders with files)
rm ................. remove files
cd ................. change current directory
man (command) ...... shows help on a specific command
talk (user) ........ pages user for chat - (user) is a email address
write (user) ....... write a user on the local system (control-c to end)
pico (filename) .... easy to use text editor to edit files
pine ............... easy to use mailer
more (file) ........ views a file, pausing every screenful
sz ................. send a file (to you) using zmodem
rz ................. recieve a file (to the unix system) using zmodem
telnet (host) ...... connect to another Internet site
ftp (host) ......... connects to a FTP site
archie (filename) .. search the Archie database for a file on a FTP site
irc ................ connect to Internet Relay Chat
lynx ............... a textual World Wide Web browser
gopher ............. a Gopher database browser
tin, trn ........... read Usenet newsgroups
passwd ............. change your password
chfn ............... change your "Real Name" as seen on finger
chsh ............... change the shell you log into
grep ............... search for a string in a file
tail ............... show the last few lines of a file
who ................ shows who is logged into the local system
w .................. shows who is logged on and what they're doing
finger (emailaddr).. shows more information about a user
df ................. shows disk space available on the system
du ................. shows how much disk space is being used up by folders
chmod .............. changes permissions on a file
bc ................. a simple calculator
make ............... compiles source code
gcc (file.c) ....... compiles C source into a file named 'a.out'
gzip ............... best compression for UNIX files
zip ................ zip for IBM files
tar ................ combines multiple files into one or vice-versa
lharc, lzh, lha .... un-arc'ers, may not be on your system
dos2unix (file) (new) - strips CR's out of dos text files
unix2dos (file) (new) - adds CR's to unix text files

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bOi_pikOt 11:29 PM [Archive]

Friday, November 17, 2006
3:15 AM

assignment#2

Operating System

DEFINITION - An operating system (sometimes abbreviated as "OS") is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. The other programs are called applications or application programs. The application programs make use of the operating system by making requests for services through a defined application program interface (API). In addition, users can interact directly with the operating system through a user interface such as a command language or a graphical user interface (GUI).

An operating system performs these services for applications:

* In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn.
* It manages the sharing of internal memory among multiple applications.
* It handles input and output to and from attached hardware devices, such as hard disks, printers, and dial-up ports.
* It sends messages to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred.
* It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from this work.
* On computers that can provide parallel processing, an operating system can manage how to divide the program so that it runs on more than one processor at a time.

All major computer platforms (hardware and software) require and sometimes include an operating system. Linux, Windows 2000, VMS, OS/400, AIX, and z/OS are all examples of operating systems.

1. What is an operating system?

An operating system is a layer of software which takes care of technical aspects of a computer's operation. It shields the user of the machine from the low-level details of the machine's operation and provides frequently needed facilities. There is no universal definition of what an operating system consists of. You can think of it as being the software which is already installed on a machine, before you add anything of your own. Normally the operating system has a number of key elements: (i) a technical layer of software for driving the hardware of the computer, like disk drives, the keyboard and the screen; (ii) a filesystem which provides a way of organizing files logically, and (iii) a simple command language which enables users to run their own programs and to manipulate their files in a simple way. Some operating systems also provide text editors, compilers, debuggers and a variety of other tools. Since the operating system (OS) is in charge of a computer, all requests to use its resources and devices need to go through the OS. An OS therefore provides (iv) legal entry points into its code for performing basic operations like writing to devices.

Operating systems may be classified by both how many tasks they can perform `simultaneously' and by how many users can be using the system `simultaneously'. That is: single-user or multi-user and single-task or multi-tasking. A multi-user system must clearly be multi-tasking. The table below shows some examples.

OS Users Tasks Processors
MS/PC DOS S S 1
Windows 3x S QM 1
Macintosh System 7.* S QM 1
Windows 9x S M* 1
AmigaDOS S M 1
hline MTS M M 1
UNIX M M $n$
VMS M M 1
NT S/M M $n$
Windows 2000 M M $n$
BeOS (Hamlet?) S M $n$
The first of these (MS/PC DOS/Windows 3x) are single user, single-task systems which build on a ROM based library of basic functions called the BIOS. These are system calls which write to the screen or to disk etc. Although all the operating systems can service interrupts, and therefore simulate the appearance of multitasking in some situations, the older PC environments cannot be thought of as a multi-tasking systems in any sense. Only a single user application could be open at any time. Windows 95 replaced the old coroutine approach of quasi-multitasking with a true context switching approach, but only a single user system, without proper memory protection. Windows NT added a proper kernel with memory protection, based on the VMS system, originally written for the DEC/Vax. Later versions of Windows NT and Windows 2000 (a security and kernel enhanced version of NT) allow multiple logins also through a terminal server. Windows 2000 thus has comparable functionality to Unix in this respect.

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bOi_pikOt 3:15 AM [Archive]