Www.ischool.drexel.edu INFO 320 Server Technology I Week 1 Server operating system and hardware concepts 1INFO 320 week 1

www.ischool.drexel.edu

INFO 320Server Technology I

Week 1

Server operating system and hardware concepts

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Overview

• This course covers basic operating system (OS), server, and architecture concepts

• Here we’ll mainly focus on server operating systems, though much of their functionality is done by any OS

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Linux and UNIX

• Much of our emphasis will be on Linux and UNIX, since that’s the OS in most servers– The labs will use the Ubuntu distribution of

Linux– What other kinds of server operating system

are there?– What kind of operating systems are there,

other than server OS’s?

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What does an OS do?

• An OS lets applications use server hardware

User

Application

OS

Hardware

CLI or GUI

API or system calls

Interrupts ordevice drivers

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Server hardware

• So the point of an operating system is to be able to access hardware

• What hardware does a server have?– What hardware characteristics do we care

about from the selection or management perspective?

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Possible traits of an OS

• What are these terms?– Multi-user OS – Multiprocessing OS– Multitasking OS

• Which of these can a server OS perform?

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Resources and Sharing

• One way to look at a computer is as a set of resources– The CPU of a computer is a resource– The memory of a computer is a resource– The keyboard of a computer is a resource– The hard disk drive of a computer is a

resource

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Why consider this way of looking at computers?

• Since the CPU of a computer operates at extremely high speeds, and since there is a speed differential between the CPU and other resources

• When the CPU is waiting for another resource, it is essentially wasting time – if the only thing that it is doing is waiting

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Resources and sharing

• On the other hand if we can have the CPU do something else while it is waiting for a resource we can make better use of the CPU resource – we won’t waste as much of the capability of the resource

• If we were to do this then we would be able to share the CPU resource among more than a single task

• The term multitasking derives from this approach• Multitasking allows us to share computer resources• The sharing of one or more computer resources is

controlled by scheduling

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What does an OS do?

• Process management

• Interrupts

• Memory management

• Storage management and disk access

• Device drivers

• Networking

• Security

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Process management

• Executing a process means creation of a process by the OS

• A task is a collection of processes

• The OS kernel creates a process by assigning it memory, and defining its priority

• Then the program is loaded into memory, and executed by the (a?) CPU

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Process management

• In order to multitask, we need a mechanism to share all of the computer resources among the tasks that require it

• The sharing requires a manager, called the kernel of the operating system

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Process management

• A process can be in three possible states

ready waiting

executing

Needs data

Gets data

Needs data

Gets data

and CPU

Gets CPU

Is preempted

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Process management

• Having multiple processes leads to the need for scheduling

• Processes are assigned priorities

• CPU time goes to highest-priority process that is ready

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Interrupts

• An interrupt is a signal informing a program that an event has occurred– Interrupts are handled by the OS kernel, and

may come from software or hardware

• When an interrupt is received, the hardware suspends whatever program is running, and might take other actions

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Interrupts

• Hardware interrupts might include– Keystrokes – Inputs from other devices (mouse, printer,

etc.)

• Software interrupts include– A program needs to get to hardware (save

a file)– Program needs more memory

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Memory management

• The OS kernel includes a memory management unit (MMU)– This makes it possible for several processes

to share main memory– An application deals with logical memory

addresses– The MMU deals with physical addresses

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Memory management

• The kernel protects memory usage via swapping, paging, and segmentation

• Swapping is when a process is temporarily moved to a backing storage location– The process is swapped out to storage, then

back in

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Memory management

• Paging manages physical memory space– Physical memory is divided into frames– Logical memory is divided into pages– Frames and pages have the same size,

defined by the hardware involved

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Memory management

• Segmentation is the mapping of logical address space for each process into segments– A segment table keeps track of each

segment’s name, length, and the offset to find its physical memory location

• Attempts to address other memory locations results in a segmentation fault interrupt

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Storage management

• All OS’s need a way to access stored data

• Data is stored on devices using files and directories

• Files are structured to allow fast access, improve reliability, and make efficient use of space

• A file system is a method for storing and organizing data

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Storage management

• OS activities include– Create and delete files and directories– Manipulate files and directories– Back up files onto storage media

• UNIX and Linux support Virtual File Systems (VFS)– Allows interoperability with Mac and Windows,

transparent to the user

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Storage management

• File system examples– Solaris uses Unix file system– Linux uses extended file system (ext4)– MS-DOS used File Allocation Tables (FAT)– Mac OS used Hierarchical File System (HFS),

and now supports Unix file systems– Windows NT/XP/Vista/7 use NT File System

(NTFS)

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Device drivers

• Device drivers allow software to communicate with specific kinds of hardware

• Each OS has drivers for each device

• Hardware manufacturers develop drivers

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Networking

• Most OS’s support various networking protocols, both open source and proprietary formats– What networking protocols might you expect

to be supported?

• Various network architectures are also supported– Client/server, peer to peer, hybrid

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Security

• Within a network, the server OS is a critical security component– Controls access to processes, and data

• Networking aspect also affects external security threats– Denial of service, worms, Trojan horses, etc.

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Security

• Within a network, security is controlled by user and group identification– User has a user ID– Belongs to a group which has a group ID– Anyone else is considered ‘other’ = outside

your group

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Security

• Each file and directory can be controlled to have different privileges for user, group, and other (u-g-o)

• The allowed privileges are – read– write (includes create, modify, or delete)– execute (application or script)

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OS Examples

• Microsoft Windows– Huge worldwide market share– Windows NT is the basis for Windows 2000,

XP, Vista, and 7, plus Windows Server 2003 and 2008

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OS Examples

• Unix– Now over 40 years old, the longest lived

family of operating systems– Mainly used in business and academia

• Sun Solaris (was SunOS)• HP HP/UX• IBM AIX• SGI IRIX (obsolete)• NeXT (obsolete, but basis for Mac OS X)

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OS Examples

• Unix-like variants– Linux– FreeBSD– openSolaris

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OS Examples

• Macintosh– System 1-9– OS X and OS X Server (based on BSD Unix)

• Mainframe OS’s– OS/400 (IBM AS/400)– DEC VMS and openVMS– OS/360 (IBM mainframes e.g. RS/6000)

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OS Examples

• Google Chrome– Based on Linux– All apps other than the OS kernel will be

delivered in a web browser– Apps and data are in the cloud, not locally

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OS Examples

• Real time OS’s– Typically used when time-predictable

response to many inputs are needed • Video or audio processing, system control

software, many complex hardware/software systems

– There are real time versions of Linux, and many other custom OS’s

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Documents

Www.ischool.drexel.edu INFO 320 Server Technology I Week 1 Server operating system and hardware concepts 1INFO 320 week 1