Computer System Basics Operating Systems: Unix, Linux, and Androids

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Computer System Basics Operating Systems Unix,
Linux, and Androids

• Lynn Choi
• Dept. Of Computer and Electronics Engineering

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Unix

• History
• Developed by Ken Thompson, Dennis Ritchie, Brian
  Kernighan, Douglas McIlroy, and Joe Ossanna at
  ATT Bell Labs in 1969
• C programming language is developed by Dennis
  Ritchie in 1973 to code UNIX
• Originally developed in assembly languages and
  recoded in C in 1973
• Widely used in servers, workstations, Macs, and
  mobile devices
• Several branches and versions available
• Unix BSD, System V, Solaris, HP-UX, AIX, OS X
• Unix-like systems Linux
• Characteristics
• Portable, multi-tasking, multi-user,
  time-sharing, client-server programming model
• Plain text for storing data
• Hierarchical file system
• Treating IO devices, IPC (interprocess
  communication) as files
• Small programs strung together through
  command-line interpreter (Shell) using pipes
• Unix philosophy keep it simple and small, make
  it modular and portable

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Unix Architecture

• Kernel (source code in /usr/sys)
• Key components of the operating system
• Boot code, device drivers, kernel, and headers
• Process management concurrency control for
  multiprocessing
• Memory management virtual memory and paging
• File management hierarchical file system
• Device and network management IO devices
  networks as files (stream of bytes)
• Programming development environment
• Cc (C compiler), as (assembler), ld (linker), lib
  (libraries), make (automatic builder),..
• Commands
• Shell command-line interpreter
• Interpret user commands and start applications
• Utilities system utilities (mkfs, fsck,..) and
  user utilities (ps, kill, ls, cp, cat, vi,..)
• Manuals and documentation

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Unix Architecture

• Shell (UI)
• Command-line interpreter
• Interpret user commands and start applications
• Utilities
• Commands
• ps, ls, vi, cat
• Libraries
• A collection of pre-written codes
• Device Drivers
• Translate high-level program calls to HW device
  commands
• Hardware dependent and OS-specific

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Evolution of the Unix operating system

• Mac OS X
• Unix-based graphical OS
• Derived from Next OS
• Objective-C (OO programming)
• Graphical UI
• IOS
• Apples mobile OS
• Used for iPhone, iPod, iPad, and Apple TV
• Derived from Mac OS X
• Touch-screen UI

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Linux

• Unix-like free and open source OS under GNU GPL
  (General Public License) based on Linux kernel
• Linux kernel was created in 1992 by Linus
  Torvalds
• Free and open source software is the primary
  difference between Linux and other OS
• GNU GPL is the most widely used free software
  license
• Copyleft license Derived works can only be
  distributed under the same license terms to
  ensure the freedoms are preserved, even when the
  work is changed or added to.
• Major platforms for mobile phones, tablet PCs,
  routers, desktops, mainframes, and supercomputers
• Smartphone platform the best selling smartphone
  platform since Q4 of 2010
• Android is based on a modified version of the
  Linux kernel
• Server platform 6 of the top 10 internet hosting
  companies run Linux while 2 of the top ten run
  FreeBSD, and the remaining 2 run MS Windows.
• Mainframe platform IBM market and sell
  Enterprise Linux Server on their mainframes
• Supercomputer platform 459 out of the top 500
  supercomputers run Linux

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Android

• Mobile OS developed by Open Handset Alliance led
  by Google
• Google purchased Android, Inc., the initial
  developer of the Android, in 2005
• OHA A consortium of 80 HW, SW, and
  telecommunication companies for the open
  standards for mobile devices
• Android code is released under the Apache
  License, a free software license
• Android Open Source Project (AOSP) is tasked with
  the maintenance and further development of
  Android
• Android system
• Consists of Android kernel, libraries APIs
  (written in C), application frameworks, Android
  runtime system including Dalvik virtual machine,
  and applications
• Android kernel is derived from Linux kernel
• Some features (i.e. power management) was
  rejected by Linux developers
• Android is a collection of middlewares built on
  top of Linux kernel
• Apps are primarily written in Java
• Dalvik Android applications are converted into
  Dalvik executable format (.dex), which is
  designed for low computing and low memory
  environment
• Unlike JVM (stack-machine), Dalvik is a
  register-based architecture

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Android Architecture