SMB a.k.a CISF

SMB/CISF

"SMB(Server Message block)" (also known as "CIFS"(Common Internet File Sharing) is a file-sharing protocol that has been used since the mid-eighties. Most people know SMB as the protocol behind the "Network Neighborhood" and remote printing in Windows. 

The SMB (Server Message Block) protocol, renamed at some point CIFS (Common Internet File System), is the protocol behind resource sharing and remote administration functionalities in Windows systems. It is implemented in all Windows NT systems. 

Over the years, several usage models for SMB have been developed. While SMB originally started out as a file sharing protocol, it was later extended to include support for network management and other network services as well. 

At a high level, the SMB protocol suite is relatively simple. It includes commands for all of the file and print operations that you might do on a local disk or printer, such as: 

· Opening and closing a file 

· Creating and deleting files and directories 

· Reading and writing a file 

· Searching for files 

· Queuing and dequeueing files to a print spool 

So conclusion is as mentioned above, the current name for SMB is CIFS, which stands for "Common Internet File System". The name suggests Microsoft's hopes for the future of the protocol suite. 

On special request of one of my Facebook friend Sumit ShashiDharan i am hereby writing article on SMB.

So, enjoy and hope you like it,kindly leave your comment. thanks

What is Virtual Memory Management

VIRTUAL MEMORY MANAGEMENT(VMM)

Real, or physical, memory exists on RAM chips inside the computer. Virtual memory, as its name suggests, doesn't physically exist on a memory chip. It is an optimization technique and is implemented by the operating system in order to give an application program the impression that it has more memory than actually exists. Virtual memory is implemented by various operating systems such as Windows, Mac OS X, and Linux.

So how does virtual memory work? Let’s say that an operating system needs 120 MB of memory in order to hold all the running programs, but there’s currently only 50 MB of available physical memory stored on the RAM chips. The operating system will then set up 120 MB of virtual memory, and will use a program called the virtual memory manager (VMM) to manage that 120 MB. The VMM will create a file on the hard disk that is 70 MB (120 – 50) in size to account for the extra memory that’s needed. The O.S. will now proceed to address memory as if there were actually 120 MB of real memory stored on the RAM, even though there’s really only 50 MB. So, to the O.S., it now appears as if the full 120 MB actually exists. It is the responsibility of the VMM to deal with the fact that there is only 50 MB of real memory.

The paging file and the RAM

Now, how does the VMM function? As mentioned before, the VMM creates a file on the hard disk that holds the extra memory that is needed by the O.S., which in our case is 70 MB in size. This file is called a paging file (also known as a swap file), and plays an important role in virtual memory. The paging file combined with the RAM accounts for all of the memory. Whenever the O.S. needs a ‘block’ of memory that’s not in the real (RAM) memory, the VMM takes a block from the real memory that hasn’t been used recently, writes it to the paging file, and then reads the block of memory that the O.S. needs from the paging file. The VMM then takes the block of memory from the paging file, and moves it into the real memory – in place of the old block. This process is called swapping (also known as paging), and the blocks of memory that are swapped are called pages. The group of pages that currently exist in RAM, and that are dedicated to a specific process, is known as the working set for that process.

As mentioned earlier, virtual memory allows us to make an application program think that it has more memory than actually exists. There are two reasons why one would want this: the first is to allow the use of programs that are too big to physically fit in memory. The other reason is to allow for multitasking – multiple programs running at once. Before virtual memory existed, a word processor, e-mail program, and browser couldn’t be run at the same time unless there was enough memory to hold all three programs at once. This would mean that one would have to close one program in order to run the other, but now with virtual memory, multitasking is possible even when there is not enough memory to hold all executing programs at once.

Storage Technology(SAN & NAS a Complete Reference)

Storage Area Network and SAN Protocols

Storage Area Network (SAN) is a high-speed network or subnetwork whose primary purpose is to transfer data between computer and storage systems. A storage device is a machine that contains nothing but a disk or disks for storing data. A SAN consists of a communication infrastructure, which provides physical connections; and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust.

Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources but may also extend to remote locations for backup and archival storage. SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and the sharing of data among different servers in a network. SANs can incorporate subnetworks with network-attached storage (NAS) systems.

There are a few SAN technologies available in today's implementations, such as IBM's optical fiber ESCON which is enhanced by FICON architecture, or the newer Fibre Channel technology. High speed Ethernet is also used in the storage Area Network for connection. SCSI and iSCSI are popular technologies used in the Storage Area Network.

A typical SAN architecture is diplayed as follows:

NAS: Network Attached Storage

Network Attached Storage (NAS) is a data storage mechanism that uses special devices connected directly to the network media. These devices are assigned an IP address and can then be accessed by clients via a server that acts as a gateway to the data, or in some cases allows the device to be accessed directly by the clients without an intermediary.NAS servers use small, specialized, and proprietary operating systems instead of general-purpose operating systems (OSs) such as the UNIX and Windows NT operating systems. Compared to the general-purpose OSs, NAS server OSs are smaller, faster, and optimized for the specialized task of file serving.

NAS servers support a variety of network file protocols such as Sun's Network File System (NFS) and Microsoft's Server Message Block / Common Internet File System (SMB/CIFS). NAS severs use open standard protocols, which allow them to interface with multiple types of client computers and operating systems.