Overview: Linux and Unix

1
Overview Linux and Unix
(OS comparison)

• Credit Cailan Hao (Lancy)
• Instructor Mort Anvari
• Date 11/3/1999
• Southeastern University

The symbol of Linux
2
Basic Linux Information
SECTION I LINUX OVERVIEW
Slide 2

• FREE (GPL Licensed), based heavily on the POSIX
  and UNIX API's.
• Supports both 32 and 64 bit hardware Provide a
  stable multi-user Internet ready OS.

Note The word Linux throughout the
presentation refers to Red Hat Linux 6.0 the
most popular type of Linux.
3
Memory Management
SECTION I LINUX OVERVIEW
Slide 3

• Linux uses the Buddy algorithm to effectively
  allocate and de-allocate blocks of pages. (Left
  Figure)
• Linux assumes that there are three levels of page
  tables.
• (Right Figure)

4
Cache Management
SECTION I LINUX OVERVIEW
Slide 4

• The role of the Linux page cache is to speed up
  access to files on disk.
• When swapping pages out to the swap files, Linux
  avoids writing pages if it does not have to.

5
How Linux Processes
SECTION I LINUX OVERVIEW
Slide 5

• Linux is a multiprocessing operating system
• Its objective is to have a process running on
  each CPU in the system at all times -maximize CPU
  utilization.
• Linux supports a number of different executable
  file formats. EX ELF and Java
• Linux can manage the processes in the system,
  each process is represented by a task_struct data
  structure

• Some common function areas
• State
• Running ready to run
• Waiting waiting for an event
• Stopped process stopped
• Zombie halted
• Scheduling Information which program most
  deserve to run
• Identifiers used to control this processes
  access to the files and devices in the system
• Times and Timers Each clock tick, the kernel
  updates the amount of time in jiffies that the
  current process has spent in system and in user
  mode

6
Linux Networking
SECTION I LINUX OVERVIEW
Slide 6

• Linux implements the internet protocol address
  family as a series of connected layers of
  software

• Linux supports the following socket address
  families or domains
• UNIX - Unix domain sockets,
• INET
• TCP/IP protocols
• AX25 - Amateur radio X25
• IPX - Novell IPX
• APPLETALK AppleTalk DDP
• X25 - X25

7
Linux PCI Initialization
SECTION I LINUX OVERVIEW
Slide 7

• The PCI initialization code in Linux is broken
  into three logical parts
• PCI Device Driver
• searches the PCI system starting at Bus 0 and
  locates all PCI devices and bridges in the
  system builds a linked list of data
• PCI BIOS
• provides the services described in
  bib-pci-bios-specification
• PCI Fix-up
• tidies up the system specific loose ends of PCI
  initialization.

8
Unix OS Structure
SECTION 2 UNIX OVERVIEW
Slide 8

• Unix is a layered operating system
• User programs interact with the kernel through a
  set of standard system calls
• Unix is a multi-user, multi-tasking operating
  system

9
Unix File System
SECTION 2 UNIX OVERVIEW
Slide 9

• You start with the root directory, denoted by /,
  at the top and work down through sub-directories
  underneath it.

10
Unix Directories Structure
SECTION 2 UNIX OVERVIEW
Slide 10

• Every directory and file is listed in its parent
  directory.
• An inode is a special file designed to be read by
  the kernel to learn the information about each
  file. function specifies the permissions on
  the file, ownership, date of creation and of last
  access and change.
• The system does not require particular
  structure for the data in the file itself.
• There's no header, trailer, label information or
  EOF character as part of the file.

11
Unix Common Control Keys
SECTION 2 UNIX OVERVIEW
Slide 11

• Control keys - used to perform special functions
  on the command line or within an editor in Unix
• S, With control keys upper and lower case are
  the same, so S is the same as s. This
  particular example is a stop signal and tells the
  terminal to stop accepting input
• EX Control-U is normally the "line-kill" signal
  for your terminal. It erases the entire input
  file.

12
Unix Shell
SECTION 2 UNIX OVERVIEW
Slide 12

• The shell - acting as a command interpreter -
  reads your terminal input and translates the
  commands into actions taken by the system.
• The shell is analogous to command.com in DOS. The
  original shell was the Bourne shell, sh. Every
  Unix platform will either have the Bourne shell,
  or a Bourne compatible shell available.
• The default prompt for the Bourne shell is (or
  , for the root user). The default prompt for the
  C shell is .

13
Similarity - File System
SECTION 3 - COMPARISON
Slide 13

• For both OS
• Separate filesystems that the system may use are
  not accessed by device identifiers (such as a
  drive number or a drive name) but instead they
  are combined into a single hierarchical tree
  structure that represents the filesystem as a
  single entity.

• Unix and Linux transparently supports many
  different filesystems (for example MS-DOS and
  EXT2) and presents all of the mounted files and
  filesystems as one integrated virtual filesystem.

14
Similarity Memory Management
SECTION 3 - COMPARISON
Slide 14

• Linux supports the Unix TM System V shared memory
  IPC.

15
Similarity - IPC
SECTION 3 - COMPARISON
Slide 15

• Inter-Process Communication
• Linux supports the classic Unix TM IPC mechanisms
  of signals, pipes and semaphores and also the
  System V IPC mechanisms of shared memory,
  semaphores and message queues.

16
Similarity Identifiers
SECTION 3 - COMPARISON
Slide 16

• Linux and Unix - uses user and group identifiers
  to check for access rights to files and images in
  the system.
• All of the files in a Linux system have
  ownerships and permissions, these permissions
  describe what access the system's users have to
  that file or directory.

17
Similarity Executing Programs
SECTION 3 - COMPARISON
Slide 17

• In both OS - programs and commands are normally
  executed by a command interpreter. (A command
  interpreter is a user process like any other
  process and is called a shell 2)
• Shells - searches the directories in the
  process's search path, held in the PATH
  environment variable, for an executable image
  with a matching name.

18
Similarity - EXT2 File System
SECTION 3 - COMPARISON
Slide 18

• A Linux filename has the same format as all Unix
  TM filenames have. It is a series of directory
  names separated by forward slashes (/'') and
  ending in the file's name.
• EX /home/rusling/.cshrc where /home and /rusling
  are directory names and the file's name is
  .cshrc.
• Like Unix TM systems, Linux does not care about
  the format of the filename itself it can be any
  length and consist of any of the printable
  characters.

19
DIFFERENCE
END NOTE THE MAJOR DIFFERENCE
Slide 19

• Although Linux share a lot of similarities with
  Unix, It is not Unix.
• Many people think Linux is a kind of Unix but
  actually, they do not come from the same source
  code base.

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Presentation Info

• Presentation designer Cailan Hao (Lancy)
• Presentation Instructor
• Mort Anvari
• Presentation content Overview Linux and Unix
  Comparison
• Presentation Slides 20

• Contact Me
• Lannee_at_zdnetmail.com
• Name Lancy
• OS Comparison Presentation
• 11/3/1999