Monday, June 30, 2008

System call in operating system

A system call is a request made by any arbitrary program to the operating system for performing tasks -- picked from a predefined set -- which the said program does not have required permissions to execute in its own flow of execution. Most operations interacting with the system require permissions not available to a user level process, i.e. any I/O performed with any arbitrary device present on the system or any form of communication with other processes requires the use of system calls.

UNIX

Unix (officially trademarked as UNIX, sometimes also written as Unix with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.
As of 2007, the owner of the trademark is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification are qualified to use the trademark; others are called "Unix system-like" or "Unix-like".

Saturday, June 28, 2008

CLEAN BOOT

CLEAN BOOT:

Starting (booting) a computer as minimalistically as possible. Typically when you start your computer, it loads many files and programs to customize your environment. A clean boot eliminates these optional features and loads only those files and programs that are absolutely required by the operating system.
A clean boot is a troubleshooting technique that allows you to get the computer up and running so that you can perform diagnostic tests to determine which elements of the normal boot process are causing problems.

COLD BOOT

Definition of: cold boot
Starting the computer by turning power on. Turning power off and then back on again clears memory and many internal settings. Some program failures will lock up the computer and require a cold boot to use the computer again.The start-up of a computer from a powered-down, or off, state. Also called a hard boot.

WARM BOOT

WARM BOOT:
Refers to restarting a computer that is already turned on via the operating system. Restarting it returns the computer to its initial state. A warm boot is sometimes necessary when a program encounters an error from which it cannot recover. On PCs, you can perform a warm boot by pressing the Control, Alt, and Delete keys simultaneously. On Macs, you can perform a warm boot by pressing the Restart button.
Also called a soft boot.
Contrast with cold boot, turning a computer on from an off position.

Information about windows xp and windows vista

Windows XP has been out since around 2002. It is more stable, programs are generally centered around running on it, and most of the security issues have been resolved and patched from being out on the market for so long. Windows Vista is Microsoft's newest operating system, released in January 2007. It's newer and has more security and added features, but since it's so new there are very few bugfixes for it and many concerns about the security and usability.However, with Vista being the newest operating system, this is the direction Microsoft is taking computers. It's not as easy to find a computer with XP on it anymore (all computers sold at Future Shop now come with Vista loaded on) and all future software should be written to support Windows Vista. Before long, there will be programs out that require Windows Vista to run. games, Halo 2 and Shadowrun, which require Windows Vista . Just like Windows XP succeeded Windows 2000 and Windows ME, Windows Vista is looking to succeed Windows XP. Put in the plainest of terms, Vista is XP's sequel

LINUX

LINUX:
Linux (pronounced /ˈlɪnəks/ or /ˈlɪnʊks/)[1] is the name usually given to any Unix-like computer operating system that uses the Linux kernel. Linux is one of the most prominent examples of free software and open source development: typically all underlying source code can be freely modified, used, and redistributed by anyone.[2]
The name "Linux" comes from the Linux kernel, started in 1991 by Linus Torvalds. The system's utilities and libraries usually come from the GNU operating system, announced in 1983 by Richard Stallman. The GNU contribution is the basis for the alternative name GNU/Linux.[3]
Predominantly known for its use in servers, Linux is supported by corporations such as Dell, Hewlett-Packard, IBM, Novell, Oracle Corporation, Red Hat, and Sun Microsystems. It is used as an operating system for a wide variety of computer hardware, including desktop computers, supercomputers,[4], and embedded devices such as E-book readers, video game systems (PlayStation 2, PlayStation 3 and XBox[5]), mobile phones and routers.

VIRTUAL MEMORY

Virtual memory is a computer system technique which gives an application program the impression that it has contiguous working memory, while in fact it may be physically fragmented and may even overflow on to disk storage. Systems that use this technique make programming of large applications easier and use real physical memory (e.g. RAM) more efficiently than those without virtual memory.
Note that "virtual memory" is not just "using disk space to extend physical memory size".

SYMBIAN PHONES

Symbian Phones
Symbian OS is the world-leading open operating system that powers the most popular and
ad anced smartphones today from the world’s leading handset manufacturers.
http://www.symbian.com/phones/index.html

Friday, June 27, 2008

Real time operating system


A real-time operating system (RTOS) is an operating system that guarantees a certain capability within a specified time constraint.

For example, operating system might be designed to ensure that a certain object was available for a robot on an assembly line. In what is usually called a "hard" real-time operating system, if the calculation could not be performed for making the object available at the designated time, the operating system would terminate with a failure.

In a "soft" real-time operating system, the assembly line would continue to function but the production output might be lower as objects failed to appear at their designated time, causing the robot to be temporarily unproductive. Some real-time operating systems are created for a special application and others are more general purpose. Some existing general purpose operating systems claim to be a real-time operating systems. To some extent, almost any general purpose operating system such as Microsoft's Windows 2000 or IBM's OS/390 can be evaluated for its real-time operating system qualities. That is, even if an operating system doesn't qualify, it may have characteristics that enable it to be considered as a solution to a particular real-time application problem.
In general, real-time operating systems are said to require:
multitasking
Process threads that can be prioritized
A sufficient number of interrupt levels
Real-time operating systems are often required in small embedded operating systems that are packaged as part of microdevices. Some kernels can be considered to meet the requirements of a real-time operating system. However, since other components, such as device drivers, are also usually needed for a particular solution, a real-time operating system is usually larger than just the kernel.

SYMBIAN OS OVERVIEW

The Symbian OS was designed specifically for mobile devices. It has a very small memory footprint and low power consumption. This is very important, as users do not want to recharge their phone daily and to allow to run on small devices with limited memory. Unlike other proprietary operating systems, it is an open OS, enabling third party developers to write and install applications independently from the device manufacturers.

HOW MEMORY MANAGEMENT UNIT WORKS

Modern MMUs typically divide the virtual address space (the range of addresses used by the processor) into pages, whose size is 2n, usually a few kilobytes. The bottom n bits of the address (the offset within a page) are left unchanged. The upper address bits are the (virtual) page number. The MMU normally translates virtual page numbers to physical page numbers via an associative cache called a Translation Lookaside Buffer (TLB). When the TLB lacks a translation, a slower mechanism involving hardware-specific data structures or software assistance is used. The data found in such data structures are typically called page table entries (PTEs), and the data structure itself is typically called a page table. The physical page number is combined with the page offset to give the complete physical address.

What are the benefits of Symbian OS?

1. Wide selection of applications available for a range of mobile phones
2. Implements industry standard protocols, interfaces and management services for IT system integration
3. Application development using industry standard Java and C++ languages
4. Extensive connectivity options - including GSM, GPRS, CDMA, WCDMA, WiFi and Bluetooth

MULTIPROCESSING

Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them.[1] There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined (multiple cores on one die, multiple chips in one package, multiple packages in one system unit, etc.).
Multiprocessing sometimes refers to the execution of multiple concurrent software processes in a system as opposed to a single process at any one instant. However, the term multiprogramming is more appropriate to describe this concept, which is implemented mostly in software, whereas multiprocessing is more appropriate to describe the use of multiple hardware CPUs. A system can be both multiprocessing and multiprogramming, only one of the two, or neither of the two.

MEMORY MANAGEMENT .

Memory management unit

This 68451 MMU could be used with the Motorola 68010A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware component responsible for handling accesses to memory requested by the central processing unit (CPU). Its functions include translation of virtual addresses to physical addresses (i.e., virtual memory management), memory protection, cache control, bus arbitration, and, in simpler computer architectures (especially 8-bit systems), bank switching.

MULTIPROGRAMMING

Multiprogramming
Multiprogramming is a rudimentary form of parallel processing in which several programs are run at the same time on a uniprocessor. Since there is only one processor , there can be no true simultaneous execution of different programs. Instead, the operating system executes part of one program, then part of another, and so on. To the user it appears that all programs are executing at the same time.
If the machine has the capability of causing an interrupt after a specified time interval, then the operating system will execute each program for a given length of time, regain control, and then execute another program for a given length of time, and so on. In the absence of this mechanism, the operating system has no choice but to begin to execute a program with the expectation, but not the certainty, that the program will eventually return control to the operating system.
If the machine has the capability of protecting memory , then a bug in one program is less likely to interfere with the execution of other programs. In a system without memory protection, one program can change the contents of storage assigned to other programs or even the storage assigned to the operating system. The resulting system crashes are not only disruptive, they may be very difficult to debug since it may not be obvious which of several programs is at fault.

TIMESHARING

Time sharing is synonymous with multi-user. Almost all mainframes and minicomputers are time-sharing systems, but most personal computers and workstations are not. Refers to the concurrent use of a computer by more than one user -- users share the computer's time.

Thursday, June 26, 2008

layers of symbian os

The Symbian OS System Model contains the following layers, from top to bottom:
UI Framework Layer
Application Services Layer
Java ME
OS Services Layer
generic OS services
communications services
multimedia and graphics services
connectivity services
Base Services Layer
Kernel Services & Hardware Interface Layer

General Questions ans Answers about Operating Systems

http://physinfo.ulb.ac.be/cit_courseware/opsys/os01.htm

Difference Between Windows 2000 and Xp

XP Professional and XP Home Edition share the same kernel (the "guts" of the operating system), and this kernel is based on the Windows 2000 operating system. The differences between them are in the level of security they provide, networking capabilities, and advanced features. For business users, Windows XP Professional is very similar to Windows 2000 in its feature set. XP Professional supports multiple processors, multiple monitors (up to 9), Group Policy. Encrypting File System, Dynamic Disks, IIS, a built in backup program, and advanced networking capabilities (such as IPSec.) All of these features are missing from XP Home Edition. Another important distinction between the two versions is that XP Home Edition cannot join a Windows NT/2000/2003 domain. If you wish to network with other PC's in your home or office, you must be part of a workgroup. If you're a "power user" purchasing Windows XP for your personal workstation, Windows XP Professional is a better choice than Home Edition, if you can afford the price difference. Windows XP Professional is also more secure than Home Edition, which is an important consideration for users with a full time high speed internet connection.
What are the differences between Windows 2000 Professional and Windows XP Professional?
Not much. Microsoft has added a host of new features to both versions of Windows XP, but nothing that appears to be absolutely compelling for business users. One of the new features called "Fast User Switching" allows to to run two separate logged in sessions at once. This allows a user to do everyday work such as e-mail using a non-privileged user account, and then run an Administrative session at the same time without rebooting or resorting to the "Run As" command. This also allows you to quickly log onto any users workstation and make administrative changes without logging them off. The remote assistance feature of XP can also help reduce support costs by allowing your Help Desk staff to interact with a user's PC over the network. XP's built in ZIP compression support can also save your company a lot of money in licensing fees if you are currently using a third party utility such as WinZIP.

The official Microsoft answer is that XP stands for "experience", in the sense that they are combining their years of experience creating two very successful desktop operating systems into one really great product. Pundits have come up with their own definitions of XP, including "eXPensive" and "eXtra Profits"

It seems that Microsoft has always configured its Operating Systems for the future generation of hardware, and XP is no exception. Unless you bought a PC recently, you'll probably want to upgrade your desktop PC before you upgrade your OS. Below is a table of bare minimum and recommended hardware requirements, as well as our "real word" recommendations.
Windows XP system requirements
Componen Bare Minimum Recommended "Real World"
CPU 233 Mhz 300 Mhz +600 Mhz
Memory 64Mb 128Mb +256Mb
Free Disk Space 1.5GB 2.0GB +8GB

DIFFERENCE BETWEEN UNIX AND WINDOWS 2000

UNIX is a much older Operating System that was designed in the 1960's. It began as an open source project that became widely used in Universities, scientific labs, and by the U.S. government. Over the years, hundreds of talented programmers contributed their own improvements to Unix making it extremely robust, stable, and fast. However, UNIX can be difficult to learn and isn't as widely supported as Microsoft Windows. For information regarding UNIX vs. Windows NT/2000 in corporate and academic environments, see http://www.unix-vs-nt.org

DEVICES THAT HAVE USED SYMBIAN OS.

On November 16, 2006, the 100 millionth smartphone running the OS was shipped.[6]
Ericsson R380 (2000) was the first commercially available phone based on Symbian OS. As with the modern "FOMA" phones, this device was closed, and the user could not install new C++ applications. Unlike those, however, the R380 could not even run Java applications, and for this reason, some have questioned whether it can properly be termed a 'smartphone'.
Nokia 9210 Communicator smartphone (32-bit 66 MHz ARM9-based RISC CPU) (2001), 9300 Communicator (2004), 9500 Communicator (2004) using the Nokia Series 80 interface
UIQ interface:
Used for PDAs such as Sony Ericsson P800 (2002), P900 (2003), P910 (2004), P990 (2005), W950 (2006), M600 (2006), P1 (2007), W960 (2007), G700 (2008), G900 (2008), G702 (2008), Motorola A920, A925, A1000, RIZR Z8, RIZR Z10, DoCoMo M1000, BenQ P30, P31 and Nokia 6708 using this interface.
Nokia S60 (2002)
Nokia S60 is used in various phones, the first being the Nokia 7650, then the Nokia 3650, followed by the Nokia 3620/3660, Nokia 6600, Nokia 7610, Nokia 6670 and Nokia 3230. The Nokia N-Gage and Nokia N-Gage QD gaming/smartphone combos are also S60 platform devices. It was also used on other manufacturers' phones such as the Siemens SX1, Sendo X, Panasonic X700, Panasonic X800, Samsung SGH-D730, SGH-D720 and the Samsung SGH-Z600. Recent, more advanced devices using S60 include the Nokia 6620, Nokia 6630, the Nokia 6680, Nokia 6681 and Nokia 6682, a next generation Nseries, including the Nokia N70, Nokia N71, Nokia N72, Nokia N73, Nokia N75, Nokia N80, Nokia N81, Nokia N82, Nokia N90, Nokia N91, Nokia N92, Nokia N93 and Nokia N95, and the enterprise (i.e. business) model Eseries, including the Nokia E50, Nokia E51 Nokia E60, Nokia E61, Nokia E62, Nokia E65, and Nokia E70. For an up to date list, refer to the Symbian S60 website.
Nokia 7710 (2004) using the Nokia Series 90 interface.
Nokia 6120 classic, Nokia 6121 classic
Fujitsu, Mitsubishi, Sony Ericsson and Sharp phones for NTT DoCoMo in Japan, using an interface developed specifically for DoCoMo's FOMA "Freedom of Mobile Access" network brand. This UI platform is called MOAP "Mobile Orientated Applications Platform" and is based on the UI from earlier Fujitsu FOMA models.

symbian os

How does Symbian OS work?
As an operating system software, Symbian OS provides the underlying routines and services for application software. For example, an email software that interacts with a user through a mobile phone screen and downloads email messages to the phone's inbox over a mobile network or WiFi access, is using the communication protocols and file management routines provided by the Symbian OS.
Symbian OS technology has been designed with these key points in mind:
to provide power, memory and input & output resource management specifically required in mobile devices
to deliver an open platform that complies with global telecommunications and Internet standards
to provide tools for developing mobile software for business, media and other applications
to ensure the wide availability of applications and accessories for different user requirements
to facilitate wireless connectivity for a variety of networks

DOS BASED WINDOWS

Windows 1.0
Windows 2.0
Windows 3.0 (the first version to make substantial commercial impact)
Windows 3.1x
Windows 3.2 (Chinese-only release)
Windows 95 (aka Windows 4.0)
Windows 98 (aka Windows 4.1)
Windows Millennium Edition (often shortened to Windows Me) (aka Windows 4.9)
OS/2 (developed jointly with IBM)
Windows NT
Windows NT 3.1
Windows NT 3.5
Windows NT 3.51
Windows NT 4.0
Windows 2000 (aka Windows NT 5.0)
Windows XP (aka Windows NT 5.1) (codename: Whistler)
Windows Server 2003 (aka Windows NT 5.2) (codename: Whistler Server)
Windows Fundamentals for Legacy PCs (aka Windows NT 5.1)
Windows Vista (aka Windows NT 6.0) (codename: Longhorn)
Windows Server 2008 (aka Windows NT 6.0) (codename: Longhorn Server)
Windows 7 (previously codenamed Blackcomb, then Vienna)
Windows Preinstallation Environment (WinPE)

DIFFERNCE BETWEEN WINDOWS 95 AND 98,2000

Windows 98 and Windows Me are based on the popular Microsoft Windows 95 Operating System, and are designed for the consumer market. Windows 95/98 were designed for backward compatibility with older DOS and 16bit programs, as well as providing a platform for the newer (back in 1995) 32 bit programs. Although many companies use both Windows 95 and Windows 98, these Operating Systems lack the security and stability of Windows NT/2000. However, Windows 95/98/Me is compatible with more software (including games) and hardware. It is important to remember that Windows 2000 is designed for the corporate environment, and not the average home use

ScreenPlay is the new graphics architecture in Symbian OS.

ScreenPlay is the new graphics architecture in Symbian OS. Designed to power the richest visual experience available on a mobile phone to date, it gives users big screen effects in their pockets while ensuring long battery life. ScreenPlay is designed for mobile devices with user interfaces which integrate high definition video content, life-like games and animations. It significantly enhances content presentation in versatile, yet simple new ways - by using transparency and overlays, for example. ScreenPlay offers high performance in a scalable fashion - working purely in software on mid-range devices and taking advantage of hardware acceleration when present on high-end devices. These enhancements are delivered without compromising the device's battery power efficiency.

MS DOS

MS DOS is a functional operating system where you type a command and it takes you to the function. Usually the F keys are used to tell the system a command, and move from page to page to access or change information. Windows has graphics and DOS does not. Windows also utilizes GUIs, which are graphical user interfaces... icons, buttons, arrows, pictures, etc... it is all graphical user interfaces... it is there for your benefit, so you can use the computer.

WINDOWS VISTA

WINDOWS Vista is Microsoft’s much anticipated new
client operating system. When released, it is due to
replace Windows XP as Microsoft’s premier desktop
operating system. Windows Vista represents a significant
departure from previous Windows systems both in terms of
its emphasis on security and its many new features. As
security has grown in importance, Microsoft has paid
increasingly more attention to it, evidenced by the
significant resource investment that has been made.
Windows Vista provides Microsoft with its first opportunity
to introduce security into the design process of the core
operating system itself. Microsoft has also chosen Windows
Vista as the platform on which to introduce many newly
developed technologies.
The Windows Vista network stack is particularly interesting
because many of its components are new. The TCP/IP
network stack itself has been rewritten and is one of Vista’s
largest departures from previous versions of Windows. The
new stack was written to allow easier maintenance,
important new performance enhancements, and improved
stability [30].

Personal Digital Assistance

A personal digital assistant (PDA) is a handheld computer, also known as small or palmtop computers. Newer PDAs also have both color screens and audio capabilities, enabling them to be used as mobile phones (smartphones), web browsers, or portable media players. Many PDAs can access the Internet, intranets or extranets via Wi-Fi, or Wireless Wide-Area Networks (WWANs). Many PDAs employ touch screen technology.

What's the difference between Windows 2000 and Windows XP?

Windows 2000 and Windows XP are essentially the same operating system (known internally as Windows NT 5.0 and Windows NT 5.1, respectively.) Here are some considerations if you're trying to decide which version to use:
Windows 2000 benefits
Windows 2000 has lower system requirements, and has a simpler interface (no "Styles" to mess with).
Windows 2000 is slightly less expensive, and has no product activation.
Windows 2000 has been out for a while, and most of the common problems and security holes have been uncovered and fixed.
Third-party software and hardware products that aren't yet XP-compatible may be compatible with Windows 2000; check the manufacturers of your devices and applications for XP support before you upgrade.
Windows XP benefits
Windows XP is somewhat faster than Windows 2000, assuming you have a fast processor and tons of memory (although it will run fine with a 300Mhz Pentium II and 128MB of RAM).
The new Windows XP interface is more cheerful and colorful than earlier versions, although the less-cartoony "Classic" interface can still be used if desired.
Windows XP has more bells and whistles, such as the Windows Movie Maker, built-in CD writer support, the Internet Connection Firewall, and Remote Desktop Connection.
Windows XP has better support for games and comes with more games than Windows 2000.
Windows XP is the latest OS - if you don't upgrade now, you'll probably end up migrating to XP eventually anyway, and we mere mortals can only take so many OS upgrades.
Manufacturers of existing hardware and software products are more likely to add Windows XP compatibility now than Windows 2000 compatibility.
Symbian OS releases:
Symbian OS is the market leading open operating system for advanced data-enabled mobile phones licensed by the world’s leading mobile phone manufacturers. It is designed for the specific requirements of advanced 3G mobile phones and beyond. Symbian OS combines the power of an integrated applications environment with mobile telephony, bringing advanced data services to the mass market. Symbian OS v9.5, the latest evolution of Symbian OS, delivers over 70 new features for high-performance, more powerful smartphones at mass market costs: a truly scalable operating system for the global market.

Latest OS

Symbian OS is the advanced, open operating system licensed by the world’s leading mobile phone manufacturers. It is designed for the specific requirements of advanced 2.5G and 3G mobile phones. Symbian OS combines the power of an integrated applications environment with mobile telephony, bringing advanced data services to the mass market.

Wednesday, June 25, 2008

Microsoft Windows

Microsoft Windows is a series of software operating systems produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs). Microsoft Windows came to dominate the world's personal computer market, overtaking Mac OS, which had been introduced previously. The most recent client version of Windows is Windows Vista. The current server version of Windows is Windows Server 2008.

Windows Vista

http://en.wikipedia.org/wiki/Windows_Vista

Kernel

The Kernel is the central component of most computer operating systems (OS). Its responsibilities include managing the system's resources (the communication between hardware and software components)
A kernel can be contrasted with a shell (such as bash, csh or ksh in Unix-like operating systems), which is the outermost part of an operating system and a program that interacts with user commands. The kernel itself does not interact directly with the user, but rather interacts with the shell and other programs as well as with the hardware devices on the system, including the processor (also called the central processing unit or CPU), memory and disk drives.
The kernel is the first part of the operating system to load into memory during booting (i.e., system startup), and it remains there for the entire duration of the computer session because its services are required continuously. Thus it is important for it to be as small as possible while still providing all the essential services needed by the other parts of the operating system and by the various application programs.

URL

Abbreviation of Uniform Resource Locator, the global address of documents and other resources on the World Wide Web.

The first part of the address is called a protocol identifier and it indicates what protocol to use, and the second part is called a resource name and it specifies the IP address or the domain name where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes.

For example, the two URLs below point to two different files at the domain pcwebopedia.com. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol:

ftp://www.pcwebopedia.com/stuff.exe
http://www.pcwebopedia.com/index.html

What is virtual machine?

Virtual Machines
The concept of virtual machines is closely related to layering.
In a typical multi-user system, users are expected to know that the machine is shared by other users, and that resources such as devices are shared between all the users.
In virtual machine operating systems an addition layer of abstraction is placed between the users and the system so that it appears to the user that they are using a machine dedicated to them.
Usually it is the case that a more powerful machine is used to host several virtual machines. For example, the 80386 and later Intel CPUs supported virtual 8086 machines. Thus, an operating system designed for the 80386 could actually run several copies of MS-DOS and appear to the user to be several different PCs at the same time.
Another example of a virtual machine system is the IBM 370 running the VM operating system. This allowed users to work as if they had a dedicated (but smaller, less powerful) 370 completely at their disposal.

CACHE MEMORY

Cache (pronounced cash) memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard’s capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.
As it happens, once most programs are open and running, they use very few resources. When these resources are kept in cache, programs can operate more quickly and efficiently. All else being equal, cache is so effective in system performance that a computer running a fast CPU with little cache can have lower benchmarks than a system running a somewhat slower CPU with more cache. Cache built into the CPU itself is referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.
Cache that is built into the CPU is faster than separate cache, running at the speed of the microprocessor itself. However, separate cache is still roughly twice as fast as Random Access Memory (RAM). Cache is more expensive than RAM, but it is well worth getting a CPU and motherboard with built-in cache in order to maximize system performance.

Graphical User Interface

A graphical user interface (GUI) is a type of user interface 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.

A program interface that takes advantage of the computer's graphics capabilities to make the program easier to use. Well-designed graphical user interfaces can free the user from learning complex command languages. On the other hand, many users find that they work more effectively with a command-driven interface, especially if they already know the command language.

Graphical user interfaces, such as Microsoft Windows and the one used by the Apple Macintosh, feature the following basic components:

  • pointer : A symbol that appears on the display screen and that you move to select objects and commands. Usually, the pointer appears as a small angled arrow. Text -processing applications, however, use an I-beam pointer that is shaped like a capital I.
  • pointing device : A device, such as a mouse or trackball, that enables you to select objects on the display screen.
  • icons : Small pictures that represent commands, files, or windows. By moving the pointer to the icon and pressing a mouse button, you can execute a command or convert the icon into a window. You can also move the icons around the display screen as if they were real objects on your desk.
  • desktop : The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop.
  • windows: You can divide the screen into different areas. In each window, you can run a different program or display a different file. You can move windows around the display screen, and change their shape and size at will.
  • menus : Most graphical user interfaces let you execute commands by selecting a choice from a menu.

The first graphical user interface was designed by Xerox Corporation's Palo Alto Research Center in the 1970s, but it was not until the 1980s and the emergence of the Apple Macintosh that graphical user interfaces became popular. One reason for their slow acceptance was the fact that they require considerable CPU power and a high-quality monitor, which until recently were prohibitively expensive.

Graphical User Interfaces also make it easier to move data from one application to another. A true GUI includes standard formats for representing text and graphics. Because the formats are well-defined, different programs that run under a common GUI can share data. This makes it possible, for example, to copy a graph created by a spreadsheet program into a document created by a word processor.

Many DOS programs include some features of GUIs, such as menus, but are not graphics based. Such interfaces are sometimes called graphical character-based user interfaces to distinguish them from true GUIs

windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement consumer versions of Windows that were based on MS-DOS. NT was the first fully 32-bit version of Windows, whereas its consumer-oriented counterparts, Windows 3.1x and Windows 9x, were 16-bit/32-bit hybrids. Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows Home Server, and Windows Server 2008 are based upon the Windows NT system, although they are not branded as Windows NT.

Saturday, June 21, 2008

definiton of deadlock

A deadlock is a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function.

SERVICES OF OPERATING SYSTEMS

An operating system performs these services for applications:
1. In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn.
2. It manages the sharing of internal memory among multiple applications.
It handles input and output to and from attached hardware devices, such as hard disks, printers, and dial-up ports.
3. It sends messages to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred.
4. It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from this work.
5. On computers that can provide parallel processing, an operating system can manage how to divide the program so that it runs on more than one processor at a time.
6.All major computer platforms (hardware and software) require and sometimes include an operating system. Linux, Windows 2000, VMS, OS/400, AIX, and z/OS are all examples of operating systems.

Functions of an Operating System

Functions of an Operating System:

.Control data and its access by processes
.Provide for efficient device access
.Manage resources
.Control user access to the machine
.Provide for efficient device access
.Perhaps 3 jobs are sent to the printer... the OS decides the order in which the jobs will be printed.
.The OS also manages information as it arrives as input.
.Manage resources
.Multi-tasking system, many processes can be run “at the same time”.
.OS decides priority of access, how many users, etc.

definition of os in other words

What is an operating system?
An operating system (sometimes abbreviated as "OS") is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. The other programs are called applications or application programs. The application programs make use of the operating system by making requests for services through a defined application program interface (API). In addition, users can interact directly with the operating system through a user interface such as a command language or a graphical user interface (GUI).

Examples of os

Examples of Operating Systems:

DOS - used on IBMs
Mac OS - used on Apples & Macs
VMS - used on VAX machines (developed by DEC)
Ultrix - could also be used on the VAX
Irix - Used on the SGI’s that comprise the gl cluster.
Ultrix and Irix are known as “flavors” of UNIX

operating system

Different Operating Systems on the Same Machine ?

It is possible to have more than one operating system available to be used on a machine.
Only one operating system is run at a time, though.
Examples:
VAX - VMS or Ultrix
IBM PCs - DOS, WIN95, or Linux

Operating Systems:

Most computers have a single operating system available.
Many operating systems are tailored for use on a specific machine with specific peripherals
Each operating system has its own command language

EVOLUTION OF COMPUTER OPERATING SYSTEMS

In the early computers there were no operating systems.
By in the early 1960s, when the commercial computer merchants started supplying the extensive apparatus for reformation of the development, execution of jobs, and scheduling on batch processing systems.
With the advancement of the time we have come across a number of operating system software.
Starting from the DOS, a lot much operating system software has got developed through out the ages like the UNIX, Oracle etc depending on the requirement.
The most commonly-used modern desktop and laptop operating system is the Microsoft Windows.
Tough more powerful servers make the use of FreeBSD, Linux, and other Unix-like systems a lot.
Though, these types of operating systems, particularly Mac OS X, are also installed on the personal computers.

real time os

A real-time operating system (RTOS)[Generally pronounced as: Are-toss] is a multitasking operating system intended for real-time applications. Such applications include embedded systems (programmable thermostats, household appliance controllers, mobile telephones), industrial robots, spacecraft, industrial control (see SCADA), and scientific research equipment.
An RTOS facilitates the creation of a real-time system, but does not guarantee the final result will be real-time; this requires correct development of the software. An RTOS does not necessarily have high throughput; rather, an RTOS provides facilities which, if used properly, guarantee deadlines can be met generally (soft real-time) or deterministically (hard real-time). An RTOS will typically use specialized scheduling algorithms in order to provide the real-time developer with the tools necessary to produce deterministic behavior in the final system. An RTOS is valued more for how quickly and/or predictably it can respond to a particular event than for the given amount of work it can perform over time. Key factors in an RTOS are therefore a minimal interrupt latency and a minimal thread switching latency.
An early example of a large-scale real-time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System.

what is BIOS ?

Acronym for basic input/output system, the built-in software that determines what a computer can do without accessing programs from a disk. On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions.
The BIOS is typically placed in a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and will not be damaged by disk failures. It also makes it possible for a computer to boot itself. Because RAM is faster than ROM, though, many computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing.
Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.
The PC BIOS is fairly standardized, so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.
PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory rather than ROM.

Friday, June 20, 2008

DOS

Definition - DOS (Disk Operating System) was the first widely-installed operating system for personal computers. (Earlier, the same name had been used for an IBM operating system for a line of business computers.)
The first personal computer version of DOS, called
PC-DOS, was developed for IBM by Bill Gates and his new Microsoft Corporation. He retained the rights to market a Microsoft version, called MS-DOS. PC-DOS and MS-DOS are almost identical and most users have referred to either of them as just "DOS." DOS was (and still is) a non-graphical line-oriented command- or menu-driven operating system, with a relatively simple interface but not overly "friendly" user interface. Its prompt to enter a command looks like this:
C:>
The first Microsoft Windows operating system was really an application that ran on top of the MS-DOS operating system. Today, Windows operating systems continue to support DOS (or a DOS-like user interface) for special purposes by emulating the operating system.
In the 1970s before the personal computer was invented, IBM had a different and unrelated DOS (Disk Operating System) that ran on smaller business computers. It was replaced by IBM's
VSE operating system.

generation of os

In an operating system generation method for a computer, at a system initiation, a kernel as the basic portion of the operating system is linked with a plurality of input-output drivers controlling input-output devices. A directory name of each driver and an address thereof in a main memory are stored in a table within the kernel with a correspondence established therebetween, which allows mutual references between the kernel and the input-output drivers and which hence enables the input-output drivers to be generated in an independent fashion with respect to the kernel. As a result, the user can incorporate desired input-output drivers into an operating system depending on a hardware configuration of the computer system.

Windows95,98,2000,XP

Windows 95
Originally it was called Memphis, and then Windows 97, but Microsoft changed the name when it realized that it was going to miss its target 1997 release date.
Windows 98 offers support for a number of new technologies, including FAT32, AGP, MMX, USB, DVD, and ACPI. Its most visible feature, though, is the Active Desktop, which integrates the Web browser (Internet Explorer) with the operating system. From the user's point of view, there is no difference between accessing a document residing locally on the user's hard disk or on a Web server halfway around the world.
Windows 98
Originally it was called Memphis, and then Windows 97, but Microsoft changed the name when it realized that it was going to miss its target 1997 release date.
Windows 98 offers support for a number of new technologies, including FAT32, AGP, MMX, USB, DVD, and ACPI. Its most visible feature, though, is the Active Desktop, which integrates the Web browser (Internet Explorer) with the operating system. From the user's point of view, there is no difference between accessing a document residing locally on the user's hard disk or on a Web server halfway around the world.
Windows 2000
A product in Microsoft's Windows line of operating systems. There are four versions of Windows 2000:
Professional -- an operating system for business desktop and laptop systems. It is used to run software applications, connect to Internet and intranet sites, and access files, printers, and network resources.
Server -- both a Web server and an office server. Windows 2000 Server lets users build Web applications and connect to the Internet.
Advanced Server -- an operating for line-of-business applications and e-commerce. It contains all the functionality of the standard version of Windows 2000 Server, plus additional features for applications that require higher levels of scalability and availability.
Datacenter Server -- developed to work in high-traffic computer networks, it is designed for enterprises that need reliable high-end drivers and software. It supports up to 64-way SMP and up to 64 GB of physical memory.
Windows 2000 is sometimes abbreviated as W2K
Windows XP
An operating system introduced in 2001 from Microsoft's Windows family of operating systems, the previous version of Windows being Windows Me. Microsoft called the release its most important product since Windows 95. Along with a redesigned look and feel to the user interface, the new operating system is built on the Windows 2000 kernel, giving the user a more stable and reliable environment than previous versions of Windows. Windows XP comes in two versions, Home and Professional. The company has focused on mobility for both editions, including plug and play features for connecting to wireless networks. The operating system also utilizes the 802.11x wireless security standard.
The "XP" in Windows XP stands for "eXPerience."

Real-time Operating System

  • A real-time operating system (RTOS)[Generally pronounced as: Are-toss] is a multitasking operating system intended for real-time applications. Such applications include embedded systems (programmable thermostats, household appliance controllers, mobile telephones), industrial robots, spacecraft, industrial control (see SCADA), and scientific research equipment.
  • An RTOS is valued more for how quickly and/or predictably it can respond to a particular event than for the given amount of work it can perform over time. Key factors in an RTOS are therefore a minimal interrupt latency and a minimal thread switching latency.
  • An early example of a large-scale real-time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System.
  • To some extent, almost any general purpose operating system such as Microsoft's Windows 2000 or IBM's OS/390 can be evaluated for its real-time operating system qualities.
  • Real-time operating systems are often required in small embedded operating systems that are packaged as part of microdevices. Some kernels can be considered to meet the requirements of a real-time operating system. However, since other components, such as device drivers, are also usually needed for a particular solution, a real-time operating system is usually larger than just the kernel.

Some Of The Uses Of Operating Systems

Some Of The Uses Of Operating Systems


An operating system (OS) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer. The operating system acts as a host for application programs that are run on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers, including hand-held computers, desktop computers, supercomputers, and even modern video game consoles, use an operating system of some type. See also Computer systems architecture.

Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation. Users may also interact with the operating system by typing commands or using a graphical user interface (GUI, commonly pronounced “gooey”). For hand-held and desktop computers, the GUI is generally considered part of the operating system. For large multiuser systems, the GUI is generally implemented as an application program that runs outside the operating system. See also Computer programming; Human-computer interaction.

Common contemporary operating systems include Microsoft Windows, Mac OS X, Linux and Solaris. Microsoft Windows has a significant majority of market share in the desktop and notebook computer markets, while the server and embedded device markets are split amongst several operating systems. [1] [2]

IN MAINFRAME WHICH OPERATING SYSTEM IS USED

Mainframe operating system: z/OS

z/OS, a widely used mainframe operating system, is designed to offer a stable, secure, and continuously available environment for applications running on the mainframe.

Mainframe operating system: z/VM

a control program, z/Virtual Machine (z/VM) is a hypervisor because it runs other operating systems in the virtual machines it creates.

Mainframe operating system: z/VSE

z/Virtual Storage Extended (z/VSE) is popular with users of smaller mainframe computers. Some of these customers eventually migrate to z/OS when they grow beyond the capabilities of z/VSE.

Mainframe operating system: Linux for zSeries
Several (non-IBM) Linux distributions can be used on a mainframe.

Mainframe operating system: z/TPF
The z/Transaction Processing Facility (z/TPF) operating system is a special-purpose system that is used by companies with very high transaction volume, such as credit card companies and airline reservation systems.

Thursday, June 19, 2008

Device controller

A device controller is a part of a computer system that makes sense of the signals going to, and coming from the CPU processor. There are many device controllers in a computer system. Any device connected to the computer is connected by a plug and socket, and the socket is connected to a device controller. Device controllers use binary and digital codes.

Basic functions of any operating system

Managing Resources – These programs coordinate all the computer’s
resources including keyboard, mouse, printer, monitor, storage devices and
memory.
Providing a user interface – Users interact with application programs and computer hardware
through a user interface. Almost all operating systems today provide a windows-like Graphical
User Interface (GUI) in which graphic objects called icons are used to represent commonly used
features.
Running applications – These programs load and run applications such as word processors and
spreadsheets. Most operating systems support multitasking, or the ability to run more than one
application at a time
Support for built-in utility programs –The operating
system uses utility programs for maintenance and repairs.
Control to the computer hardware – The operating system sits between the programs and the
Basic Input Output System (BIOS).
More informations: http://schoolnet.gov.mt/cs/Resources/Sam%20Cefai/operating%20system%202.pdf

Linux

*Linux is the name usually given to any Unix-like computer operating system that uses the Linux kernel.
*Linux is one of the most prominent examples of free software and open source development: typically all underlying source code can be freely modified, used, and redistributed by anyone.
*The name "Linux" comes from the Linux kernel, started in 1991 by Linus Torvalds.
*The system's utilities and libraries usually come from the GNU operating system, announced in 1983 by Richard Stallman. The GNU contribution is the basis for the alternative name GNU/Linux.
*Predominantly known for its use in servers, Linux is supported by corporations such as Dell, Hewlett-Packard, IBM, Novell, Oracle Corporation, Red Hat, and Sun Microsystems.
* It is used as an operating system for a wide variety of computer hardware, including desktop computers, supercomputers and embedded devices such as E-book readers, video game systems, mobile phones and routers.