SEB070023-TUTORIAL 5

Magnetic Disk

Description:
On magnetic disks, data is encoded as
microscopic magnetized needles on the disk's surface. Data can be record and
erase on a magnetic disk any number of times, just as with a cassette

tape.

Advantage:
Although the variance in DASD access times
isn’t as wide as with magnetic tape, the location of the specific record still
has a direct effect on the amount of time required to access it.

Fixed-Head Magnetic disk

Looks like a
large CD or DVD covered with magnetic film.

Formatted,
usually on both sides, into tracks. Data is
recorded serially on each track by the fixed read/write head positioned
over it

Advantage:

·
Faster than the movable –head disks

·
These devices are used when speed
is of the utmost importance such as spacecraft monitoring or aircraft
application

Movable-Head Magnetic
Disk Storage

Have one
read/write head that floats
over the surface of each disk. It
can be a single platter.
It can be a part
of a disk pack (stack
of platters)

Examples:

Floppy disk :

A typical 5¼-inch floppy
disk can hold 360K or 1.2MB (megabytes).
3½-inch floppies normally

store 720K, 1.2MB or 1.44MB of data.

Hard
disk :

Hard disks can store
anywhere from 20MB to more than 200GB. Hard disks are also from 10 to 100 times
faster than floppy disks.

Removable
cartridge : Removable cartridges are hard disks encased in a metal or
plastic

cartridge, so you can remove them
just like a floppy disk. Removable cartridges are very fast, though usually not
as fast as fixed hard disks

Optical Disk

Description:
An optical disc is an electronic data storage medium that can be written to and
read using a low-powered laser beam.

Advantage:
· An optical disc holds much more data.

· The greater control and focus possible with laser beams (in
comparison to tiny magnetic heads) means that more data can be written into a
smaller space.

· Storage capacity increases with each new generation of optical
media.

· Emerging standards, such as Blu-ray, offer up to 27 gigabytes (GB) on a single-sided 12-centimeter disc. In comparison, a diskette, for example, can hold 1.44 megabytes (MB).

·Optical discs are inexpensive to manufacture and data stored on them is relatively impervious to most environmental threats, such as power surges, or magnetic disturbances.

Examples:

CD-ROM

Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times, but CD-ROMs cannot be modified.

CD-Rewritable

Data can be written, changed, and erased using phase change technology

DVD technology

DVD-ROMs can store more data, are smaller, and the spiral is wound tighter than CD ROMs

CD-RW

Offers the advantages of a DVD-ROM drive and a
CD-RW drive in a single unit that ca play DVD movies and audio CDs

Blu-rays

Flash Memory

Description:
Removable medium that emulates random access memory

Advantage:
· Flash drives are impervious to scratches and dust, and mechanically very robust making them suitable for transporting data from place to place and keeping it readily at hand.

·
Allow user to store data on
microchip card and move it from device to device as they would magnetic or
optical storage media.Data
are store securely even its removed from its power source.

Examples:

Pen drive

Memory card

Magneto-Optical Disks

Description:

It combines the technology of magnetic disks with that of optical discs. A kind
of

optical disc drive capable of
writing and rewriting data upon a magneto-optical disc.

Advantage:

·
MO disks can store up to several GB
of data and their access rate is faster than that of a floppy disk but slower
than that of hard drives.

·
These disks are hardier than
optical discs.Unlike
a CD, this process does not cause a physical change to the disk and because the
change is not permanent, changes can be made many times

Examples:

CD-ROMs

                                              
Date:  26 August 2008

 The key to using
memory efficiently is virtual memory management. Consider both Windows and a
UNIX/Linux operating system. Compare and contrast how each implements virtual
memory. Describe how each one handles page faults, page sizes and how it
reconciles thrashing issues. Cite your sources.

 

Answer:

 Virtual
memory makes the system appear to have more memory than it actually has by
sharing it between competing processes as they need it. Systems
that use this technique make programming of applications easier and use physical
memory (e.g.

RAM) more
efficiently than those without virtual memory.

 Compare
and contrast how each implements virtual memory 

Windows

UNIX/Linux

Windows NT and its variants employ a dynamically allocated page file for memory management. A page file is allocated on disk, for less frequently accessed objects in memory, leaving more RAM available to actively used objects. This scheme suffers from slow-downs due to disk fragmentation, which hampers the speed at which the objects can be brought back into memory when they are needed. Windows can be configured to place the page file on a separate partition; doing this negates the disk-fragmentation issues, but introduces an I/O slowdown due to the seek time involved in switching back and forth between the two partitions. However, the main reason this is not done by default is that, if the page file is on a separate partition, then Windows cannot create a memory dump in the event of a Stop Error. The ideal solution performance-wise is to have the page file on a separate hard drive to the primary one, which eliminates both defragmentation and I/O issues. In memory management, for example, Windows NT 5.0 and its successors use clustered paging, a working set memory analogue and a free memory manager that fires up exactly once per second, •         Paging –        Available –        Reserved –        Committed

Most hard drive installations of Linux utilize a "swap partition", where the disk space allocated for paging is separate from general data, and is used strictly for paging operations. This reduces slowdown due to disk fragmentation from general use. As with Windows, for best performance the swap partition should be placed on a separate hard drive to the primary one. Unix uses an adaptive page specific algorithm to control paging. In Unix, there is no working set equivalent, and the free memory manager runs when needed

 

Paging are
performed when a program tries to access pages that do not currently reside in
RAM

 

Thrashing is swapping out a
piece of a process just before that piece is needed.
The processor spends most of its time swapping pieces rather than
executing user instructions

 

Windows	UNIX/Linux
Page faults Windows uses structured exception handling to report page fault-based invalid accesses as access violation exceptions. Recent Windows versions also write a minidump (similar in principle to a core dump) describing the state of the crashed process for later analysis alongside such less-technical error messages	Typically use signals, to report these error conditions to programs. . UNIX operating systems typically report these conditions to the user with error messages such as "segmentation violation", or "bus error".
Page sizes Win32-based operating system, such as Windows 9x, NT use the system function GetSystemInfo()from kernel32.dll. Windows NT provides a page-based virtual memory management scheme that allows applications to realize a 32-bit linear address space for 4 gigabytes (GB) of memory. As a result, each application has its own private address space from which it can use the lower 2 GB—the system reserves the upper 2 GB of every process's address space for its own use.	UNIX systems use the system function sysconf(), as illustrated in the C programming language.The Unix kernel divides the memory into manageable chunks called pages. A single page of memory is usually 4096 or 8192 bytes (4 or 8KB). Memory pages are laid down contiguously across the physical and virtual memory.
Thrashing  The total number of pages is being used by this particular instruction is eight, and all eight pages must be present in memory at the same time. If the operating system will allocate less than eight pages of actual memory in this example, when it attempts to swap out some part of the instruction or data to bring in the remainder, the instruction will again page fault, and it will thrash on every attempt to restart the failing instruction. To resolve thrashing due to excessive paging, a user can do any of the following. 1. Increase the amount of RAM in the computer 2. Decrease the number of programs being run on the computer.

 

 

Resourse:
• http://en.wikipedia.org/wiki/Page_size
• http://members.shaw.ca/bsanders/WindowsGeneralWeb/RAMVirtualMemoryPageFileEtc.htm 1.1.
• http://www.cs.uml.edu/~cgould/#Memory%20Management
• http://www.michaelhorowitz.com/Linux.vs.Windows.html

SEB070023-Toturial 3

Explain 20 core functions of an operating system in your own thoughts.

1. It manages the hardware and software resources of the system include such things as the processor,memory, disk space and others.
2. It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware-Application Programming Interface
3. Serve as a platform for other application. Operating systems offer a number of services to application programs and users.
4. Give users access to practically any program they could run on a computer's desktop.Such as Word processing programs, Games, Spreadsheet programs and others
5. Used in distant learning, banking, online games and others.
6. Memory management.It manages the sharing of internal memory among multiple applications
7. Device management.It manage and maintain the devices
8. Process management.In multitasking environment, OS determines which program should run in order and fairly allocated the processor time
9. Operating system controls and schedules for execution by the CPU
10. User interface provides a link between the user and the computer
11. OS is needed in starting the computer
12. Networking
13. Creating a file system.OS choses those locations, and recorded them.A user needs to copy, move, delete, and rename files.
14. Acts as resource allocator and manager.The operating system directs the traffic inside the computer, deciding what resources will be used and for how long.
15. Operating system controls the user programs to prevent errors and improper use of the computer especially concerned with the operation and control of I/O devices.
16. Provides support for the loading and execution of other programs
17. Enable virtual memory operations for application programs which both allows flexible use of memory and enforces security
18. Security.OS not only relieves the application programmer from having to perform the physical accesses of the disk, but also forbids us from doing so. So the applications programmer wont either inadvertently or maliciously trash someone else's disk file, for instance.
19. System performance.Used to monitor computer performance, debug problems, or maintain parts of the system.
20. Operating system can manage the programs so that it runs on more than one processor at a time.

SEB070023-Tutorial 2

Define the following terms :
1) Application software
A computer program designed to carry out a specialized task for the user such as database management, word processing or electronic mail
Examples: Media player
Microsoft Office

2) Communication device

Wearable devices
Examples: Microphone
Webcam

3) Computer
An electronic machine which is used for storing, organising and accept data, process data, and for controlling other machine
Examples: Laptop
Computer

4) Desktop computer
A view on a computer screen which is intended to represent the top of a desk and which contains icons that represent files, programs and other features of the computer

5) Embedded computer
Special purpose computer system designed to perform one or few dedicated functions usually embedded as part of a complete device including hardware and mechanical parts
Examples: Traffic light
Washing machine
Airbag

6) Graphical User Interface
A user interface based on graphics instead of text. Uses a mouse as well as a keyboard as an input
Examples: Icons

Pictures


7) Hardware
The physical and electronics parts of a computer rather than the instructions it follows
Examples: Mouse
Monitor
Motherboard

8) Internet
An interconnected system of network that connects computers around the world via the TCP/IP protocol

9) Installing
To connect or set in position and prepare for use
Examples: Install software on the computer

10) Network
A collection of computer or devices connect together often wirelessly via communicating devices