Transcript UNIX
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 equalsized “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 = 126.8 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 • UNIX System V series V.2 IBM AIX BSD 4.2 Apollo V.3 4.3 V.4.1 OSF/1 SUN OS (Solaris) HP/UX IEEE POSIX ANSI Standard: POSIX: Portable Operating System Interface for Computer Environments. It involved the standard about system calls and interfaces.