UNIX Operating System

A Brief Review of Computer System 1. The Hardware CPU, RAM, ROM, DISK, CD-ROM, Monitor, Graphics Card, Keyboard, Mouse, Printer, Tape, Modem, Network Interface, and many others. 2. The Software File, Program, Process, Directory Structure, and many more.

Unix Hierarchical Directory Structure Root Home Bin

Important Philosophy of UNIX Do one thing and do it well in one process (or utility).

***Sharing System Resources The very important feature for UNIX operating system is the capability of sharing system resources. Among all the resource sharing, timesharing is the most important concept.

Resource Sharing 1. CPU time sharing among processes are divided into many slices (typically 1/10 per user ). 2. For important processes, they will get more slices than the less important ones. Example: 1. How many processes can a CPU run in 1 minute of time?

Memory Sharing RAM is divided into thousands of equal- sized “pages” of memory. Only those portions of a process that actually need to be in RAM are ever loaded from disk.

External Memory Sharing UNIX shares disk space among users in a similar fashion.

Multi-User System Because of the ever-increasing of CPU speed, more users can access UNIX at a given time frame. Example: If a computer has a CPU of 4GHz CPU clock, it takes 1000 cpu clock time to serve a single user, how many users can be served in 1 second?

Calculation 4GHz = 4,000,000,000 cycles/second 4,000,000,000/1,000 = 4,000,000 That means 4 million users can access the computer in 1 second (strictly speaking, not the same time).

Visualize the Speed of Modern CPU Example: For the same CPU we mentioned, if we try to count the clock pulses created by the CPU in one second one pulse a second, how long will it take for a human to do that?

The Numbers 4,000,000,000 seconds 4,000,000,000/60 = 66,666,666 minutes 66,666,666/60 = 1,111,111 hours 1,111,111/24 = 46,296 days 46,296/365 = years ! And that was only the number of pulses created by the CPU in 1 second.

Communication in UNIX Many levels of communications: 1. Among different processes. 2. Between processes and I/O’s. 3. Between different users and/or systems. : :

X Server and X Clients X – Window System X – Server and X – Clients

UNIX Utilities Because of its old age and popularity, UNIX has many utilities for many different purposes. Standard UNIX comes complete with at least 200 small utility programs.

“OPEN” System Concept “Open” means that the internal software architecture is well documented and available in source code form, either: Free of charge (Linux) A relatively small fee (regular UNIX).

Files in UNIX Unix treats almost everything as a file. 1. Your program is a file. 2. A directory is a file. 3. A floppy drive is a file. 4. A hard disk drive is a file, too.

Pipeline in UNIX 1. Pipeline in general meaning. 2. Pipeline in Computer system. 3. Pipeline in UNIX.

UNIX Standards Two main paths: 1. System V (AT&T) 2. BSD (Berkeley Standard Distribution)

The General Picture BSD System V series UNIX V.2 V.3 V IBM AIX OSF/1 SUN OS (Solaris) HP/UX Apollo

IEEE POSIX ANSI Standard: POSIX: Portable Operating System Interface for Computer Environments. It involved the standard about system calls and interfaces.