11. operating-systems-part-1

IT Infrastructure Architecture
Operating Systems – Part 1
(chapter 11)
Infrastructure Building Blocks
and Concepts

Introduction
• An operating system is
the set of programs
that, after being initially
loaded into a computer
by a boot program,
controls all the other
programs in a computer

Introduction
• Operating systems manage a computer’s internal workings
– Memory
– Processors
– Internal and peripheral devices
– File system
• Operating systems are used on for instance::
– PCs and laptops
– Virtual machines
– Servers
– Tablets and mobile phones
– Network routers
– Storage arrays
– Cars
– Televisions

Introduction
• Operating systems provide an abstraction layer
between (virtualized or physical) hardware and
software applications
• As a service to applications, low level hardware
management is handled by the operating system
– Process management
– Memory management
– Interrupt handling
– Multi user management
– File locking and file sharing

Introduction
• Operating systems provide services to
applications in the form of Application
Programming Interfaces (APIs)
• For example for:
– File management
– I/O interfaces (like video and keyboard)
– Hardware drivers (like printer drivers)

History
• Early operating systems could execute one program at
a time
• At any given time, one user had sole use of the
computer
• Through the 1950s, many major features were
pioneered in the field of operating systems, including
multitasking
• During the 1960s, IBM introduced a single operating
system (OS/360) for all of its mainframes
• In 1969, UNIX was created
– UNIX used a file system with directories
– Standard POSIX system calls

History
• An early operating systems for personal
computers was CP/M
– CP/M introduced drive letters (c:), but no directories
• Parts of CP/M and UNIX were imitated in MS-DOS
– Drive letters and directory structures
– System calls
– MS-DOS became extremely popular when chosen as
the default operating system for the IBM PC
• The most popular operating systems running on
servers today are Microsoft Windows, Linux, and
UNIX

Operating system building blocks

Operating System building blocks
• An operating system basically performs two
basic operations:
– It enables multiple users, multiple processes, and
multiple applications to run together on a single
piece of hardware
– It hides the technical complexities of the
underlying hardware from the applications
running on top of the operating system

• The kernel is the heart of an
operating system
– Starts and stops programs
– Manages the file system
– Performs low level tasks that
most programs need
• The kernel schedules access to
hardware to avoid conflicts if
two programs try to access the
same resource or device
simultaneously

• Drivers are small applications that
connect specific hardware devices to
the kernel
– Printers
– Network cards
– Keyboard and mouse
– Video screens
• Utilities are applications that are
considered part of the operating
system
– User interfaces
– Logging tools
– Editors
– System update processes

• Applications consist of one or
more processes that communicate
with the operating system using
system calls that are invoked
through Application Programming
Interfaces (APIs)

Process scheduling
• Operating systems create the illusion of multiple
running processes in parallel by scheduling each
process to run only during a short time frame
– This principle is also known as preemptive multitasking
– Periodically, the operating system decides if a running
process is to be suspended in favor of another process, or
if the running process can keep on running for a while
• Process scheduling is fairly complex
– Must be well-balanced
– Switching processes introduces some overhead
– The scheduling algorithm guarantees each process gets
its fair share of CPU time
– Because operating systems have evolved over decades,
scheduling algorithms are very sophisticated

File systems
• The operating system provides a file system
to applications
– File systems usually consist of directories (also
known as folders) with files or other directories
• The operating system hides complexity
– Handling individual disk blocks or communication
with a SAN or NAS
– Managing the files and the directory structure
– Security – permission to read, write, create, and
delete files and directories

File systems
• Most operating systems can handle multiple
types of file systems on multiple disks at the
same time
• Some popular file systems are:
– FAT (File Allocation Table), vFAT, and FAT32, used in
MS-DOS, older versions of Windows, and removable
storage devices like USB memory sticks
– NTFS (New Technology File System) used in Windows
– UFS (Universal File System) and VxFS (Veritas File
System) used in most UNIX flavors
– Ext (and Ext2, Ext3, Ext4) - used in Linux

File systems
• Journaling file systems keep track of changes made to files
in a journal log before committing them to the main file
system
– Higher availability
– Fast recovery in case of a malfunction
• File systems must be mounted before they can be used by
the operating system
– A disk and the file system on it must be recognized by the
operating system and attached to it
• After mounting, the file system is typically given either:
– A drive letter (Windows)
– A drive name (OpenVMS)
– A mount point in the global directory tree (UNIX and Linux)

File systems
• Most operating systems provide file sharing
functionality
– File sharing enables files on one system to be
accessed by (users on) other systems
– File sharing protocols:
• NFS: originates from UNIX
• SMB/CIFS: originates from Windows

APIs and system calls
• System calls are programming functions
– Provide a hardware-independent interface to tasks
the operating system can perform for applications
• Example:
int read(int handle, void *buffer, int
nbyte);
translates into the system call
READ(FILEHANDLE, DESTINATION DATA
POINTER, NUMBER_OF_BYTES)

• The operating system takes care of:
– Looking-up the file in a file allocation table
– Looking up the disk blocks on disk
– Instructing the disk controller to fetch the
needed disk blocks
– Copy the disk blocks to memory
– Providing a pointer to the disk blocks in memory

• System calls are grouped and presented to
application processes as Application
Programming Interfaces (APIs)
• APIs describe the available system calls in an
operating system and how they can be used
by programmers in their applications
• Each operating system has its own API
– UNIX and Linux use the POSIX standard
– Windows has its own API

Device drivers
• The operating system
manages all hardware
• I/O devices are controlled
using device drivers
– Pieces of software that
interact with the device's
hardware (like an Ethernet
network adapter or a SAS
disk adapter)
– They provide an Application
Programming Interface (API)
to the operating system

Memory management
• The operating system:
– Allocates and de-allocates memory on behalf of applications
– Manages what happens when the amount of requested
memory exceeds the physical amount of memory
• Memory management includes:
– Cache management
– Paging
– High volume data transfers
– Memory management units (MMUs)
– Thin memory provisioning (memory overcommitting)
– Direct Memory Access (DMA)
• The operating system takes care of all of this and just
provides chunks of memory to applications

Shells, CLIs and GUIs
• A shell provides a user interface to the operating
system
– The primary purpose of shells is to launch other programs,
started by end users or scripts
• Two types of shells:
– Command-Line Interfaces (CLIs)
• The user types commands on a keyboard on a command-prompt
• Examples: UNIX shells (bash, sh, csh) and Windows’ cmd.exe (also
known as a DOS box)
– Graphical User Interfaces (GUIs)
• The user uses a mouse to click on icons or buttons
• Examples Microsoft Windows and X Windows (UNIX and Linux)

Operating system configuration
• The configuration of an operating system is
stored in an operating system specific database
or in text files
• Examples:
– Windows registry
– Files in the Linux /etc directory
– AIX Object Data Manager (ODM) database
• For most used configuration parameters, user-
friendly tools are provided
– These tools still edit the text files, but that is hidden
from the user

IBM z/OS
• The most used mainframe operating system
• Extreme backward compatibility is one of z/OS's
main design philosophies
– Programs written for MVS in 1974 can still run on
today's z/OS without modification
• Typical use of z/OS:
– Batch processing: reading and writing large amounts
of data and performing relatively simple calculations
on it
– Interactive users: supports thousands of interactive
users

IBM i (OS/400)
• IBM i is an operating system only used on IBM's Power
Systems midrange systems
– The operating system was previously known as OS/400
– The midrange system was previously known as AS/400
• One of the biggest advantages of IBM i is its
completeness, it includes:
– Communications
– Transaction processing
– Relational database manager
– Features for the implementation and maintenance of data
security
• The latest version is "IBM i 7.2“, released in 2014

OpenVMS
• OpenVMS is an operating system developed by
DEC
– VMS means Virtual Memory System
– OpenVMS is now maintained by VMS Software, Inc.
• OpenVMS is a multi-user operating system
designed for:
– Time sharing
– Batch processing
– Real-time processing
– Transaction processing
• OpenVMS is not open source software
– The source listings are available for purchase

OpenVMS
• OpenVMS is typically used in environments
where system uptime and data access is critical
• It is used for various applications, including:
– Mail servers
– Network services
– Manufacturing
– Transportation control and monitoring
– Critical applications
– Databases
• OpenVMS for HP Integrity servers based on Intel
Itanium 9500 processors was released in 2015

UNIX - History
• UNIX is a multitasking, multi-user operating system
• Created by Bell Labs (now AT&T) in 1969
• In 1973, UNIX was rewritten in the new C programming
language
– C was created by the same people that created UNIX
– This made UNIX portable to multiple types of computer
hardware
• In 1982, UNIX was licensed to a number of computer
manufacturers
– Most marketed their own UNIX versions based on the
original UNIX source code
– They adapted the code to meet their own hardware and
software requirements

UNIX – vendor versions
• Vendors came up with different names for their UNIX
flavors
• These versions are 90% the same, but have some
minor differences
– Wording of error messages
– The order of commands used to start-up the machine
– The location of certain files
Vendor UNIX flavor
IBM AIX
Oracle/Sun Solaris
HP HP-UX
Apple
Mac OS X (built on FreeBSD,
discussed in the next section)

• Each flavor needs specific hardware
– HP-UX only runs on HP Integrity systems
– HP systems cannot run for example IBM’s AIX
• Applications running on a particular flavor of
UNIX cannot run on another flavor without (at
least) recompiling
– Software vendors must provide separate versions
of their applications for each flavor of UNIX

• UNIX has been ported to a wider variety of
machine architectures than any other operating
system
– UNIX is written almost entirely in the C programming
language
– Source code is published
• Many business software today is released on
Linux before being released on the various flavors
of UNIX
– Linux runs on many hardware platforms without
recompiling
– Linux is now more widely used than UNIX

UNIX - filesystem
• UNIX popularized the hierarchical file system with
nested subdirectories – the directory tree
• All files and directories appear under the so-
called root directory "/“
– Even if they are stored on different physical disks
• UNIX has no concept of drive letters, like
Windows or DOS
– Drives are mounted on a branch in the directory tree,
providing disk space for that particular branch
– Also removable drives must be mounted in the tree

UNIX – system tools
• The UNIX philosophy is to use a large set of small
tools that do only one thing, and do it very well
• To perform complicated tasks, commands can be
combined using a system called pipes
– Pipes feed the output of one command to the input of
another command, without storing the intermediate
result
– For instance, the UNIX command: ls | sort prints
a sorted list of files on the screen
• The pipe sign “|” sends the output of the “ls” command as
input to the “sort” command
• In practice, these chains of piped commands can
get very long and complex

Linux - history
• Linux is a free UNIX-like operating system for the x86
platform
• It is not derived from the UNIX source code
• In 1991, Linus Torvalds wanted to explore the multitasking
possibilities of the new Intel 80386 CPU in his PC
• He decided to create a small multitasking, multi-user
operating system with the help of the internet community
• Because of the open source nature of Linux many
developers contributed
– Kernel patches
– Device drivers
– Multilingual keyboards
– Disk drivers
– Support for video card devices

Linux
• Linux commands and scripts are almost similar to those of
UNIX
• Linux also uses the same commands, file structure,
scripting language, pipes, etc. as UNIX
• Today Linux is a very mature operating system, used in:
– Servers
– Workstations
– Mobile devices
– All Android smartphones
– Appliances like set-top boxes, firewalls and NAS devices
• Ninety-five per cent of the supercomputers listed in the top
500 list of the fastest computers in the world are running
Linux
• Almost all internet services run on Linux

Linux – GNU/Linux
• The GNU project was launched in 1984 by Richard Stallman
– Goal was to develop a free UNIX-like operating system
– GNU is a recursive acronym for “GNU's Not UNIX!”
– By 1990, the GNU project had recreated all the major
components of the UNIX-like system except one – the kernel
• Combining Linux with the GNU system resulted in a
complete operating system: the GNU/Linux system
– It is important to understand that Linux is actually only an
operating system kernel
– Wat we call Linux, is actually GNU/Linux
• Linux and the GNU tools are licensed under the GNU
General Public License
– Ensures all source code will be free for all to copy, study, and to
change

Linux – distributions
• Vendors compiled the Linux source code,
added some tools and configurations of their
own, and releasing it in a distributable format
• Some of the best-known Linux distributions:
– Red Hat
– SuSe
– Ubuntu
– Debian

Linux - Support
• Linux can be downloaded from the internet
for free
• Most organizations demand professional
support for their software
• Professional support is not free
• Most Linux distribution vendors, like Red Hat
and SuSe, and some independent vendors,
offer support contracts for Linux

Linux on mainframes
• Some Linux distributions can be used on IBM
mainframes, running in virtual machines
• Linux uses X-Windows emulators on PCs to
connect to the mainframe
• The emulated LAN on the mainframe can be
used to connect multiple Linux virtual
machines and to provide an external LAN
route

BSD
• Berkeley Software Distribution (BSD) is a UNIX
operating system derivative
– Developed and distributed by the University of California,
Berkeley
• BSD was the basis for three open source development
projects:
– FreeBSD
• Most widely used
• FreeBSD is a complete operating system (Linux is only a kernel!)
– NetBSD
• Ported to 57 hardware platforms across 15 different processor
architectures
• Often used in embedded systems

BSD
– OpenBSD
• Most secure BSD version
• Has a tradition in which developers audit the source code for
software bugs and security problems
• In the 10+ years of its existence, only three security bugs
have been found in OpenBSD
• Darwin, the system on which Apple's Mac OS X is
built, is a derivative of FreeBSD

11. operating-systems-part-1

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