SEB070012-Tutorial 5

STORAGE DISKS

Magnetic Disk

Images:

Description:
Magnetic disk uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.

Examples:
Hard disk, digital tape, floppy disk

Advantages:
-High storage capacity
-Reliable
-Gives direct access to data


Optical Disk
Images:

Description:
Optical disk is a flat, circular disc (usually polycarbonate) wherein data are stored in the pits (or bumps) in its flat surface; sequentially on the continuous, spiral track extending from the innermost track to the outermost track, covering the entire disc surface. The data are accessed in the disc when a special material (often aluminium) is illuminated with a laser diode. The pits distort the reflected laser light. So most optical disks characteristically have an iridescent appearance created by the grooves of the reflective layer.

Examples:
Compact disk(CD), DVD, blue-ray disk.

Advantages:
-Much sturdier than tape or a floppy disk.
-Physically harder to break or melt or warp.
-Not sensitive to being touched, though it can get too dirty or scratched to be read. It can be cleaned.
-Entirely unaffected by magnetic fields.
-Hold much more data than floppy disk.


Flash Memory
Images:

Description:
Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once.

Examples:
Memory stick(MS), smart media(SM), compact flash(CF), security digital(SD).

Advantages:
-Does not have the mechanical limitations and latencies of hard drives.
-Low power consumption
-No moving parts
-Nearly instantaneous access times


Magneto-optical Disk
Images:

Description:
Magneto-optical disks are a hybrid storage medium. In reading, spots with different directions of magnetization give different polarization in the reflected light of a low-power laser beam. Magneto-optical disks need lasers to write data to the discs and magnetic heads to read data from the discs.

Examples:
six LMR1300 5.25" Magneto Optical disks, HP Magneto-Optical Disk Write-once 2.6 GB 92290F, Sony 5.2GB Magneto-Optical MO Disk Unit RMO-S551

Advantages:
-Data authenticity and integrity
-Long-term data retention
-High capacity and scalability
-Rapid information access.

SEB 070012 - Tutorial 4

Virtual Memory: Windows VS Linux

Virtual Memory	Windows	Linux
Implement of virtual memory How each one handles page faults, page sizes How it reconciles thrashing issues.	All processes running under 32 bit Windows gets virtual memory addresses ( virtual address space) going from 0 to 4 GB, no matter how much RAM is actually installed on the computer. 2 GB of this virtual address space are designated for each process’ private use and the other 2 GB are shared between all processes and the operating system. requires elevated privileges, cooperation from the application making the large allocation (usually setting a flag to ask the operating system for huge pages), or manual administrator configuration; operating systems commonly, sometimes by design, cannot page them out to disk. Windows Server 2003 (SP1 and newer), Windows Vista and Windows Server 2008 support huge pages under the name of large pages, but Windows XP does not. When the memory in use by all the existing processes exceeds the amount of RAM available, the operating system will move pages (4 KB pieces) of one or more virtual address spaces to the computer’s hard disk Windows uses structured exception handling to report page fault-based invalid accesses as access violation exceptions. If the program that received the error does not handle it, then Windows typically performs some sort of default action, typically involving the termination of the running process that caused the error condition, and a notification to the user that the program has malfunctioned. To prevent thrashing, Windows provide a process with as many frames as it needs. Windows will also increase the amount of RAM in the system to eliminate the cause of trashing. Besides, it also reduce the amount of RAM needed by reconfiguring the applications, removing unneeded system services, or running fewer applications at a time.	Virtual memory divides the virtual address space into equal-sized pieces called virtual pages. Virtual pages have a fixed size that is an integer power of 2. Linux can be configured to use a size of 4, 8, 16, or 64 kb to maximize the performance. Linux kernel creates and maintains page table and also employs the CPU memory management unit (MMU) to translate the virtual address of a process into physical address in order to store the data. Linux has supported huge pages on several architectures since the 2.6 series. Linux could create appropriate page-table entries whenever a range of virtual memory is allocated. However, this is wasteful because most programs allocate much more virtual memory than they ever use at any given time. So Linux uses a method called demand paging. With this, the virtual address space starts out empty. Page fault is intercepted by the Linux kernel and causes the page fault handler to be activated. Linux uses signals, such as SIGSEGV, to report these error conditions to programs. Because Linux uses demand paging and page-fault-based optimizations such as copy-on-write, page faults occur during the normal course of operation and do not necessarily indicate an error. Thus, when the page fault handler is invoked, it first needs to determine whether the page fault is caused by an access to a valid page. If not, the page fault handler simply sends a segmentation violation signal to the faulting process and returns. Otherwise, it takes one of several possible actions: -If the page is being accessed for the first time, the handler allocates a new page frame and initializes it, e.g., by reading its content from disk. Page faults caused by first-time accesses are called demand_page_faults. -If the page has been paged out to swap space, the handler reads it back from disk into a newly allocated page frame. -If the page fault occurred because of a page-fault-based optimization (such as copy-on-write), the handler takes the appropriate recovery action (such as performing the delayed page copy). Linux picks a page frame that backs a virtual page that has not been accessed recently, writes it out to a special area on the disk called the swap space, and then reuses the page frame to back the new virtual page. Then marked the page swapped out as not present. Linux can support multiple swap space areas, each of which can be either an entire disk partition or a specially formatted file on an existing file system. With this swapping method, thrashing is reconciled.

References:
http://www.informit.com/articles/article.aspx?p=29961
http://en.wikipedia.org/wiki/Virtual_memory
http://en.wikipedia.org/wiki/Page_fault
http://support.microsoft.com/kb/555223
http://en.wikipedia.org/wiki/Page_size#Page_size_trade-off

SEB070012 - Tutorial 3

Core Functions of an Operating System


1. Recognizing input from the input hardware.

2. Sending output to the display screen, normally monitor.

3. Keep files and directories on the disk.

4. Control peripheral devices such as disk drive and printer.

5. Make sure that different programs or users that run at the same time do not interfere each other in the memory in used.

6. Ensure that unauthorized users do not access the system.

7. Act as the host for application program to run on the computer.

8. handle the details of the operation of the hardware to relieve application programs from having to manage these details and makes it easier to write applications.

9. Support the running/execution of programs by the users.

10. Schedules the activities of the CPU and resources and make job more efficient and to prevent deadlock .

11. Provides an additional working memory on USB flash devices and can be combined with SuperFetch.

12. Support a variety of networking protocols. This means computers with different type of operating system are also able to connect to each other.

13. Gives information about the status of operation of each application to the user and sends messages about the errors that may have occurred .

14. Transforms the the physical world of devices, instructions, memory, and time into virtual world (graphical).

15. Creating a file system which enable the user to manage the file and its document (rename, copy, paste, cut, delete, relocate, etc.)

16. Provide a medium of interaction between computer and user.

17. Provide System tools (programs) used to monitor computer performance, debug problems, or maintain parts of the system.

18. Temporarily store application memory which is accessed less frequently on disk or other media to make the space available for other programs.

19. Ensure that all programs are given regular time on the CPU. This implies that all programs must be limited in how much time they are allowed to spend on the CPU without being interrupted.

20. Distinguish between requests which should be allowed to be processed, and others which should not be processed.

21. Provides a set of libraries or functions which programs may use to perform specific tasks especially relating to interfacing with computer system components.

Detail Functions of Operating System

1. Act as the base when running the application software.

OS acts as the base of application software. Application program is like the branches, it can't grow out if there is no trunk. So OS is like the trunk of a tree. Both OS and application software must work together to get the fruits (work done).

2. Handle the details of each hardware.

As a host of a computer, one of the purposes of the operating system is to handle the details of hardware. This relieves the application software from having to manage the details and therefore it is easier to write an application.

3. Program execution

Support the running program by the users is the basic function of the operating system. In a multiprogramming operating system, running program is normally referred to as processes. Process management refers to the facilities provided by the operating system to support the creation, execution, and destruction of process, and to facilitate different kind of interaction, and limit others.

4. Handle interrupts

In modern operating system, interrupts are handled by the operating system's kernel (the central component of most computer OS). Interrupts may come from either computer hardware or a running program. When either of them triggers the interrupt, the OS kernel decides how to deal with this event, generally by running some process code, or just ignoring it.

5. Memory management

The multiprogramming OS's kernel is responsible in managing all the system memory which in use by programs. This is to ensure a program does not interfere the memory that is already used by another running program. Since programs are used at the same time, each program must has an independant access to the memory.

6. Virtual memory addressing

Virtual memory addressing means the kernel can choose which memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. In modern OS, application memory which is accessed less frequently can be temporarily stored in disk or other media to make that space available for other programs.

7. Networking

Operating systems support a variety of networking protocols. This means that computers running dissimilar operating systems can participate in a common network for sharing resources such as files, printer, scanner, wireless connection, etc.

SEB070012 Tutorial 1

Application software:
A computer program that designed to carry out a specialised task. It makes us easier to perform our works. For example: database management, microsoft office, window media player, etc.

Communication device:
Terminal that is used to send voice, video or text to another terminal. This is inclusive of both input devices and output devices which provide accessibility of information to enter or be presented. Example terminal: handphone, computers, PDA,etc.

Computer:
A programmable machine that performs high-speed processing of numbers as well as text, graphic, symbols. It also manipulates data according to a list of instructions. A device operates under the control of instructions stored in its own memory, that can accept data, process the data according to specified rules, produce and store results.

Desktop computer:
A personal computer that is small enough to fit in a individual workspace, in a form intended for regular use at a single location.

Embedded Computer:
Special-purpose computer that functions as a component in a larger product, perform various funcitons, depending on the requirements of the product in which they reside.

Graphical User Interface:
A graphical user interface is a type of user interface (controls how you enter data and instructions and how info is displayed on the screen) which allows people to interact with electronic devices like computers, hand-held devices (MP3 Players, Portable Media Players, Gaming devices), household appliances and office equipment that interact with software using text, graphics and visual images such as icon.

Hardware:
The physical part of a computer which do a specific part of job to let the computer to run, including its digital circuitry, as distinguish from the computer software that execute within the hardware.

Internet:
Worldwide collection of networks that connects businesses, gov agencies, edu int, and indi. One of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks.

Installing:
Installation (or setup) of a program (including drivers) is the act and the effect of putting the program in a computer system so that it can be executed. It can also define as a process of setting up software to work with computer, printer, and other hardware components.

Network:
A computer network is an interconnected group of computers. A collection of computers and devices that connected via communication devices and transmission media.

Dream

Do you have dream?
I do not mean the dream you had when you are sleeping...I mean something you want to achieve in your life.
Dream do make people to have the strength to do things which lead to thier dream.
Dream do also make people become more confident.
The most important...
dream let people to have thier living values which means for what they are living for...

Do you have dream?
If yes, you are great!!
Go straight for your dream...don't wait...keep moving and moving towards it.

If no, you should start to think of your dream and have it.
Think of things that you hope for when you are young...
Think of things you believe when you are young or maybe until now you still believe it to be happened...
Think of things that make yourself to have a value in this society...
For sure there will be at least one of them is your dream...
When you get it...do the same...go straight for it...
Go through whatever that block your way...

Good luck :)