COMPUTERS AND OPERATING SYSTEMS CONCEPTS

• computer
• an electronic machine that can be supplied with a program and can store and recall information, and can perform various processes on it (Longman Dictionary of Contemporary English)

• computer hardware – the machine
• collection of well connected pieces
• CPU – usually just a chip with many legs (pins)
• diagram
• memory – a collection of storage areas
• input/output devices – where humans usually access (touch) the computer - e.g. keyboard, displays, printers, disks etc
• control devices – determine the sequence of operations
• connecting wires – buses - connect various pieces

• hardware is not easily usable on its own

• program
• plan of operations
• series of steps a computer goes through to carry out a task
• runs as a process
• usually stored on disk but runs from memory

• software – a collection or set of programs

• hardware combined with software make up the computer as we know it

• Basic Operating System Concepts

• operating system (OS)
• basically this is just a computer program
• or it is a group of programs that work together to perform the following
• house-keeping functions
• run accessories
• translate or interpret high level language programs
• perform commands
• automate and optimise the running of a computer

• operating system is usually the first program loaded into the computer when it is started

• once loaded some portions of it remain permanently in memory while the computer is running jobs

• other portions are swapped in and out of memory when facilities are required by users and resources like memory are demanded

• operating systems are needed for the following:

• to provide a high level interface so that the hardware of the computer becomes more readily usable

• user friendliness
• user access
• protection of resources and operations

• to provide the most cost effective use of the hardware
• speed
• effective - does not crash often
• manages devices well

• operating system can be viewed as a layered object like an ONION
• at the centre is the nucleus of basic facilities – the KERNEL
• additional layers are added to the kernel as required to provide more sophisticated or more convenient facilities
• examples
• DOS: command.com - acts as kernel
• LINUX: /vmlinuz - is the kernel
• kernels handle the basic devices:
• memory, keyboard, display, disks
• software drivers are added to provide access to other devices
• more disks, printers, graphics, modems, cdroms, networking
• what devices and services the kernel handles internally varies among systems
• networking is integral to UNIX but not to DOS
• graphics (GUI) is integral to Windows 95/98/NT but not to UNIX

• general features of an operating system
• convenient input/output operations: GUI, printers, disks etc
• fault monitoring – error handling – eg. on user programs
• nobody is perfect
• multi-access (multi-user)
• allowing several people to use the computer simultaneously
• more convenient for users
• sharing optimises usage of resources
• sharing of resources done in a controlled and safe manner
• file systems
• operating system provides a means for users to store/retrieve their information in an orderly manner
• directories and files
• security of user files
• operating systems used on almost all computers: PCs, mainframes, workstations, servers etc

• most work is now done on PCs and workstations

• look at common examples of operating systems

• DOS
• Disk Operating System
• only really provides a files system – as name implies
• virtually no resource protection
• no multi-tasking
• little fault monitoring
• little convenience in input/output
• no built-in networking
• commercial product

• Windows 3.x
• added Graphic User Interface (GUI) to DOS
• basic operating system is DOS with all its imperfections
• improved user convenience
• some multitasking
• little protection
• no built-in networking
• commercial product

• Windows 95 (98)
• different OS from DOS but provides some DOS and Win 3.x compatibility
• improved convenience – better GUI
• easier addition and management of resources like devices and drivers
• integrates some basic networking support
• built in Internet clients
• support for Internet protocols – TCP/IP
• still basically single user
• some crude multi-tasking
• little process protection
• commercial product

• Windows NT
• all the advantages of Windows 95 including GUI
• different operating system from Windows 95
• fully multi-tasking
• more advanced networking than Windows 95
• incorporates Internet client/server capabilities
• supports Internet protocols – TCP/IP
• networking applications based on NETBIOS and the associated NETBUI protocol
• BIOS – basic input/output system available on PC’s, DOS etc
• NETBIOS – extends input/output over a network
• NETBUI
• NETBIOS Extended User Interface
• includes NETBIOS plus additions done by IBM and Microsoft
• comes as
• single user for high end PCs
• multi-user on network servers – limitations – security problems
• commercial product

• UNIX – LINUX
• LINUX is a UNIX clone running on PC and workstations
• multi-tasking
• multi-user
• better user process and resource protection
• many arguable advantages over Windows NT
• more robust system
• better process logging
• built in networking – TCP/IP
• better device drivers
• FREE and down-loadable from Internet
• several freely available applications
• ideal for research & development environments
• disadvantage – less friendly user interface but GUIs under development

• we use LINUX extensively for both servers and clients

• Malawi SDNP regional nodes will run LINUX

• the LINUX kernel – introduction – diagrams

• Devices and Drivers

• Devices
• refer mostly to hardware items
• hard disks, floppies or stiffies
• printers
• modems
• network cards
• screens and consoles, keyboards
• etc
• DOS and WINDOWS: com1, com2, lpt:, c:, a: etc
• LINUX
• devices are referenced as files in the /dev directory e.g.
• /dev/hda2 – second (2) partition of the first (a) IDE drive
• /dev/ttyS0 – serial port equivalent to COM1 on DOS
• /dev/eth0 – ethernet card etc
• when you access a device file
• kernel recognises the input/output request
• passes it to a device driver
• device driver actually performs the operation
• device driver
• is actually a computer program (software) that performs the operation
• usually specific to device and its manufacturer
• common drivers exist
• kernel communicates with physical device through the software device driver
• drivers include
• block devices
• storage space is divided into equally sized blocks
• block size is usually 512 or 1024 bytes
• blocks can be read in any order
• e.g. IDE hard disks, SCSI hard disks, CDROMs, floppies
• character devices
• input/output in streams of data
• examples
• non-storage devices: keyboard, screen, mouse, serial ports
• sequential storage devices: tape drives
• special: /dev/null, /dev/zero
• normally not accessed directly – made available at login by kernel
• ports
• need to use this name carefully
• in DOS it refers to a particular type of device e.g. serial and printer port
• in Internet use it refers to a socket offering a particular service
• we will use the Internet and UNIX networking sense of ports
• smtp mail (e-mail) runs on port 25 under TCP
• WEB runs on TCP port 80, etc
• Programs, Processes, Daemons and TSRs
• program
• a sequential set of computer instructions that can be run on a computer
• stored on disk or memory
• not necessarily running
• process
• a particular active instance of a program
• a running program
• the same program can be run in a multitasking and multi-user OS repeatedly by one or several users at the same time thus creating several distinct processes
• a daemon is a process that runs in the background to support a particular device or service
• often used on UNIX
• e.g. printer drivers, Internet servers: mail, web, DNS etc
• TSR – terminally stay resident
• a program that is loaded and runs in the background to operate and maintain a particular device
• term usually used in DOS environments
• usually loaded from config.sys
• conclusion
• hardware and software work together to form and operate computers
• operating systems form the heart of performing jobs and making services available to users using the physical devices on the computer
• several platforms are available for computer networking
• Windows offer the most widely used and preferred user interface available for users to access computer and network services
• UNIX offers the most robust server environment for implementing network servers that offer services to other computers and users
• LINUX offers a freely available version of UNIX