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.
Friday, June 27, 2008
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.
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
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
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
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