Different Types Of Operating Systems

A basic list of the different types of operating systems


GUI

Short for Graphical User Interface, a GUI Operating System contains graphics and icons and is commonly navigated by using a computer mouse

Some examples of GUI Operating Systems

• System 7.x
• Windows 98
• Windows CE
  

Multi-user

A multi-user Operating System allows for multiple users to use the same computer at the same time and/or different times.

Some examples of multi-user Operating Systems

• Linux
• Unix
• Windows 2000

Multiprocessing

An Operating System capable of supporting and utilizing more than one computer processor.
Some examples of multiprocessing Operating Systems

• Linux
• Unix
• Windows 2000

Multitasking

An Operating system that is capable of allowing multiple software processes to run at the same time.
Some examples of multitasking Operating Systems.

• Unix
• Windows 2000

Multithreading

Operating systems that allow different parts of a software program to run concurrently. Operating systems that would fall into this category are:

• Linux
• Unix
• Windows 2000

Graphical User Interface

Most modern computer systems contain Graphical User Interfaces. In some computer systems the GUI is integrated into the kernel—for example, in the original implementations of Microsoft Windows and Mac OS, the graphical subsystem was actually part of the kernel. Other operating systems, some older ones and some modern ones, are modular, separating the graphics subsystem from the kernel and the Operating System. In the 1980's UNIX, VMS and many others had operating systems that were built this way. Today Linux, and Mac OS X are also built this way.


Many computer operating systems allow the user to install or create any user interface they desire. The X Window System in conjunction with GNOME or KDE is a commonly found setup on most Unix and Unix-like (BSD, Linux, Minix) systems. Numerous Unix-based GUIs have existed over time, most derived from X11. Competition among the various vendors of Unix (HP, IBM, Sun) led to much fragmentation, though an effort to standardize in the 1990s to COSE and CDE failed for the most part due to various reasons, eventually eclipsed by the widespread adoption of GNOME and KDE. Prior to open source-based toolkits and desktop environments, Motif was the prevalent toolkit/desktop combination (and was the basis upon which CDE was developed).


Graphical user interfaces evolve over time. For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 2001.

Please follow these links for details on other tasks performed by Operating System:
Memory Management
Process Management
Disk and File Management
Networking
Security
Graphical User Interface
Device Driver Management

Networking

Current operating systems generally support a variety of networking protocols. Most are capable of using the TCP/IP networking protocols. This means that computers running dissimilar operating systems can participate in a common network for sharing resources such as computing, files, printers, and scanners using either wired or wireless connections.


Many operating systems also support one or more vendor-specific legacy networking protocols as well, for example, SNA on IBM systems, DECnet on systems from Digital Equipment Corporation, and Microsoft-specific protocols on Windows. Specific protocols for specific tasks may also be supported such as NFS for file access.

Please follow these links for details on other tasks performed by Operating System:
Memory Management
Process Management
Disk and File Management
Networking
Security
Graphical User Interface
Device Driver Management

Device driver

A device driver is a specific type of computer software developed to allow interaction with hardware devices. Typically this constitutes an interface for communicating with the device, through the specific computer bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the operating system and software applications. It is a specialized hardware-dependent computer program which is also operating system specific that enables another program, typically an operating system or applications software package or computer program running under the operating system kernel, to interact transparently with a hardware device, and usually provides the requisite interrupt handling necessary for any necessary asynchronous time-dependent hardware interfacing needs.


The key design goal of device drivers is abstraction. Every model of hardware (even within the same class of device) is different. Newer models also are released by manufacturers that provide more reliable or better performance and these newer models are often controlled differently. Computers and their operating systems cannot be expected to know how to control every device, both now and in the future. To solve this problem, OSes essentially dictate how every type of device should be controlled. The function of the device driver is then to translate these OS mandated function calls into device specific calls. In theory a new device, which is controlled in a new manner, should function correctly if a suitable driver is available. This new driver will ensure that the device appears to operate as usual from the operating systems' point of view for any person.

Please follow these links for details on other tasks performed by Operating System:

Memory Management

Process Management

Disk and File Management

Networking

Security

Graphical User Interface

Device Driver Management

Security

Many operating systems include some level of security. Security is based on the two ideas that:


The operating system provides access to a number of resources, directly or indirectly, such as files on a local disk, privileged system calls, personal information about users, and the services offered by the programs running on the system;


The operating system is capable of distinguishing between some requesters of these resources who are authorized (allowed) to access the resource, and others who are not authorized (forbidden). While some systems may simply distinguish between "privileged" and "non-privileged", systems commonly have a form of requester identity, such as a user name. Requesters, in turn, divide into two categories:


Internal security: an already running program. On some systems, once a program is running it has no limitations, but commonly the program has an identity which it keeps and is used to check all of its requests for resources.


External security: a new request from outside the computer, such as a login at a connected console or some kind of network connection. To establish identity there may be a process of authentication. Often a username must be quoted, and each username may have a password. Other methods of authentication, such as magnetic cards or biometric data, might be used instead. In some cases, especially connections from the network, resources may be accessed with no authentication at all.


In addition to the allow/disallow model of security, a system with a high level of security will also offer auditing options. These would allow tracking of requests for access to resources (such as, "who has been reading this file?").


Internal security
Internal security can be thought of as protecting the computer's resources from the programs concurrently running on the system. Most operating systems set programs running natively on the computer's processor, so the problem arises of how to stop these programs doing the same task and having the same privileges as the operating system (which is after all just a program too). Processors used for general purpose operating systems generally have a hardware concept of privilege. Generally less privileged programs are automatically blocked from using certain hardware instructions, such as those to read or write from external devices like disks. Instead, they have to ask the privileged program (operating system kernel) to read or write. The operating system therefore gets the chance to check the program's identity and allow or refuse the request.

External security
Typically an operating system offers (or hosts) various services to other network computers and users. These services are usually provided through ports or numbered access points beyond the operating system's network address. Services include offerings such as file sharing, print services, email, web sites, and file transfer protocols (FTP), most of which can have compromised security.

At the front line of security are hardware devices known as firewalls or intrusion detection/prevention systems. At the operating system level, there are a number of software firewalls available, as well as intrusion detection/prevention systems. Most modern operating systems include a software firewall, which is enabled by default. A software firewall can be configured to allow or deny network traffic to or from a service or application running on the operating system. Therefore, one can install and be running an insecure service, such as Telnet or FTP, and not have to be threatened by a security breach because the firewall would deny all traffic trying to connect to the service on that port.


An alternative strategy, and the only sandbox strategy available in systems that do not meet the Popek and Goldberg virtualization requirements, is the operating system not running user programs as native code, but instead either emulates a processor or provides a host for a p-code based system such as Java.


Internal security is especially relevant for multi-user systems; it allows each user of the system to have private files that the other users cannot tamper with or read. Internal security is also vital if auditing is to be of any use, since a program can potentially bypass the operating system, inclusive of bypassing auditing.

Please follow these links for details on other tasks performed by Operating System:
Memory Management
Process Management
Disk and File Management
Networking
Security
Graphical User Interface
Device Driver Management

Disk and file system management

Generally, operating systems include support for file systems, which allow the user to segment a given area of memory (sometimes RAM, but usually a disk) into individual files.


Modern file systems comprise a hierarchy of directories. While the idea is conceptually similar across all general-purpose file systems, some differences in implementation exist. Two noticeable examples of this are the character used to separate directories, and case sensitivity.
Unix demarcates its path components with a slash (/), a convention followed by operating systems that emulated it or at least its concept of hierarchical directories, such as Linux, Amiga OS and Mac OS X. MS-DOS also emulated this feature, but had already also adopted the CP/M convention of using slashes for additional options to commands, so instead used the backslash (\) as its component separator. Microsoft Windows continues with this convention; Japanese editions of Windows use ¥, and Korean editions use ₩.[1] Prior to Mac OS X, versions of Mac OS use a colon (:) for a path separator. RISC OS uses a period (.).

Unix and Unix-like operating systems allow for any character in file names other than the slash and NUL characters (including line feed (LF) and other control characters). Unix file names are case sensitive, which allows multiple files to be created with names that differ only in case. By contrast, Microsoft Windows file names are not case sensitive by default. Windows also has a larger set of punctuation characters that are not allowed in file names.


File systems may provide journaling, which provides safe recovery in the event of a system crash. A journaled file system writes information twice: first to the journal, which is a log of file system operations, then to its proper place in the ordinary file system. In the event of a crash, the system can recover to a consistent state by replaying a portion of the journal. In contrast, non-journaled file systems typically need to be examined in their entirety by a utility such as fsck or chkdsk. Soft updates is an alternative to journaling that avoids the redundant writes by carefully ordering the update operations. Log-structured file systems and ZFS also differ from traditional journaled file systems in that they avoid inconsistencies by always writing new copies of the data, eschewing in-place updates.


Many Linux distributions support some or all of ext2, ext3, ReiserFS, Reiser4, GFS, GFS2, OCFS, OCFS2, and NILFS. Linux also has full support for XFS and JFS, along with the FAT file systems, and NTFS.


Microsoft Windows includes support for FAT12, FAT16, FAT32, and NTFS. The NTFS file system is the most efficient and reliable of the four Windows file systems, and as of Windows Vista, is the only file system which the operating system can be installed on. Windows Embedded CE 6.0 introduced ExFAT, a file system suitable for flash drives.


Mac OS X supports HFS+ with journaling as its primary file system. It is derived from the Hierarchical File System of the earlier Mac OS. Mac OS X has facilities to read and write FAT16, FAT32, NTFS, UDF, and other file systems, but cannot be installed to them.


Common to all these (and other) operating systems is support for file systems typically found on removable media. FAT12 is the file system most commonly found on floppy discs. ISO 9660 and Universal Disk Format are two common formats that target Compact Discs and DVDs, respectively. Mount Rainier is a newer extension to UDF supported by Linux 2.6 kernels and Windows Vista that facilitates rewriting to DVDs in the same fashion as has been possible with floppy disks.

Process Management

A program running on a computer, whether visible to the user or not, is commonly referred to as a process. Process management refers to the facilities provided by the OS to support the creation, execution, and destruction of processes.

Creating a process involves allocating memory space for the process, loading the program's executable code into memory, telling the scheduler to run the program, and other tasks specific to the operating system.


The scheduler is the portion of the operating system that causes the program to be executed on the CPU, that is, 'scheduled' for execution. If the scheduler supports preemptive multitasking, it can change the program currently executing on the CPU to that of another program when it determines that the first program has executed for a predetermined amount of time. The amount of time allocated to a given process may depend on the needs of the process in question and the user's priority level for that process.


Destroying a process involves releasing any resources (including dynamically allocated memory, file references, and I/O ports) held by the program and ensuring that a different program is scheduled for execution.


Depending on the operating system, process management can be more simple or more complex than treated above. Several examples will illustrate:


The operating systems originally deployed on mainframes, and, much later, the original microcomputer operating systems, only supported one program at a time, requiring only a very basic scheduler. Each program was in complete control of the machine while it was running.


Multitasking (timesharing) first came to mainframes in the 1960's and to microcomputers in the mid-1980's, although, in both cases, for the most part, it wasn't until years later that the capability was perfected and made widely available.


Classic Mac OS generally supported only cooperative multitasking, Application programs running with classic Mac OS must yield CPU time to the scheduler by calling a special function for that purpose.


Classic AmigaOS did not properly track resources allocated by processes at runtime. If a process had to be terminated, the resources would be lost to programs run in the future, until the machine was restarted.

Please follow these links for details on other tasks performed by Operating System:
Memory Management
Process Management
Disk and File Management
Networking
Security
Graphical User Interface
Device Driver Management

Memory Management On Operating Systems

Memory management is the act of managing computer memory. In its simpler forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. The management of main memory is critical to the computer system.


Virtual memory makes the system appear to have more memory than it actually has by sharing it between competing processes as they need it. Virtual memory does more than just make your computer's memory go further.Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using disk swapping. The quality of the virtual memory manager can have a big impact on overall system performance.

Garbage collection is the automated allocation, and deallocation of computer memory resources for a program. This is generally implemented at the programming language level and is in opposition to manual memory management, the explicit allocation and deallocation of computer memory resources The principal goals of the operating system's memory management are:
to provide memory space to enable several processes to be executed at the same time to provide a satisfactory level of performance for the system users to protect each programs resources to share (if desired) memory space between processes to make the addressing of memory space as transparent as possible for the programmer.


Memory management systems on multi-tasking operating systems usually deal with the following issues.


Relocation


In systems with virtual memory, programs in memory must be able to reside in different parts of the memory at different times. This is because when the program is swapped back into memory after being swapped out for a while it can not always be placed in the same location. Memory management in the operating system should therefore be able to relocate programs in memory and handle memory references in the code of the program so that they always point to the right location in memory.


Protection


Memory protectionProcesses should not be able to reference the memory for another process without permission. This is called memory protection, and prevents malicious or malfunctioning code in one program from interfering with the operation of other running programs.


Sharing


Shared memoryEven though the memory for different processes is protected from each other different processes should be able to share information and therefore access the same part of memory.


Logical Organization


Programs are often organized in modules. Some of these modules could be shared between different programs, some are read only and some contain data that can be modified. The memory management is responsible for handling this logical organization that is different from the physical linear address space. One way to arrange this organization is segmentation.

Physical Organization


Memory is usually divided into fast primary storage and slow secondary storage. Memory management in the operating system handles moving information between these two levels of memory.

Please follow these links for details on other tasks performed by Operating System:

Memory Management

Process Management

Disk and File Management

Networking

Security

Graphical User Interface

Device Driver Management

Maximum Message Size For Web Services (.NET 3.5)

A new introduction to .NET 3.5 is the ability to limit the size of the incoming messages when using Web services. Apparently this is to help combat Denial of Service (DoS) attacks.

However, it is not clear how to change this setting, its simple when you know how. In you App.Config, or Web.Config you should have a Bindings section for each of web services references. Within this there are all sorts of useful settings, however by default the maximum message size is quite small, so to alter this you must change maxBufferSize and maxRecievedMessageSize. Now don't go crazy just up it to what you may need, this may be quite large if you are building all your internal applications through a web service layer.

C# Coalesce

Although this has been around for a long time and this is slightly off topic, I needed it this week, and just think it is worth mentioning. With objects you occasionally need to know if they are null, and if they are get something else, or do something else. This used to be very convoluted with .NET 1.1:

if (a != null)
{
return a;
}
else if (b != null)
{
return b;
}
else if (c!= null)
{
return c;
}
else
{
return new object();
}

Now you can simply use this (.NET 2.0 and above):

return a ?? b ?? c ?? new object();

Now you can not use this with types that get default values, such as Integer's, or boolean's, however still very usefull.