Introduction to UNIX

Intro to OS

What is OS?

• software that sits between hardware and other software
• core part is called the “kernel”
• ex) Windows, Linux, Mac OS

What does OS do?

• a dictator and a servant at the same time
• controls hardware resources and logical resources
• provides a (virtual) environment in which programs run
  • linear address space
  • exclusive use of CPU
  • hardware devices that responds to nice, easy commands

How does OS do that?

• privileged operations (aided by CPU)
• periodic timer interrupts
• predefined entry points into the kernel: system calls

History of UNIX

1945–1970:

• vacuum tubes
• mainframes with punch cards
• IBM 360
• MULTICS

1970: Ken Thompson & Dennis Ritchie invent UNIX and C at Bell Labs

• most of UNIX was written in C rather than in assembly
• inexpensive source code license to universities
• UNIX V6 in 1976, V7 in 1978

Since then, many UNIX variants come and go

• AT&T System V Release 4 (SVR4)
• 4.4BSD (Berkeley Software Distribution)
• and many others: Microsoft Xenix, IBM AIX, HP-UX, IRIX, etc.

Currently, four main competitors remain:

• Linux: created by Linus Torvalds in 1991
• Solaris: SVR4-based commercial offering by Sun
• FreeBSD: based on 4.4BSD
• Mac OS X: combo of Mach kernel and FreeBSD

In the meantime, OS for personal computers evolved in parallel:

• 1977: CP/M by Kildall - dominant OS for 8-bit PCs
• 1977: Apple II by Steve Jobs and Steve Wozniak
• Early 80s: MS-DOS for IBM PC by Microsoft
• 1984: Apple Macintosh
• 1985–1996: NeXT by Steve Jobs
  • precursor to Mac OS X
• Late 80s & early 90s: MS Windows up to 3.11
  • graphical shell on top of MS-DOS
• Mid 90s to the present: Windows NT, 2000, XP, 7, 8, 10
  • true 32/64-bit OS comparable to UNIX
• 2001-present: Mac OS X

Last updated: 2018–01–18