A server message block (SMB), also known as a common Internet file system (CIFS), is a protocol used on computer networks that enables users to share access to files, ports, and printers on the system, facilitating communication between individuals connected to the same network. Additionally, it provides an inter-process communication platform, allowing processes to exchange threads of data among one another while they are running. A server message block is a client-side approach to network communications, which means that everything occurring on the network is driven by the individual client computers' requests.
Under a client-side configuration, while all computers on the network are plugged into a main "server" computer, that server computer takes on a mostly passive role. When things on the network are proceeding normally, the server will not act until requests are made by individual client computers, such as a request to access a shared file stored on the server drive or a request to funnel information from network computer A to network computer B. At all other times where the server is not under direct control by an end user, it simply sits and waits for orders to arrive.
On local area networks (LANs), server message block communication is generally considered comparable in speed to other standard protocols for passing data. On wide area networks (WANs), such as the Internet, latency has a substantial effect on server message block communications when compared to competing types of file transport protocols, such as the file transport protocol (FTP). Latency is simply the length of time it takes for a communication to take place, which is typically measured in milliseconds. A lower latency provides less of a "laggy" feeling when sending information, increasing the smoothness of the information transfer.
Additionally, even on local area networks, SMB communication results in a substantial increase in broadcast traffic. This traffic originates indirectly through the NetBIOS protocol on the system, as the server message block system itself does not produce broadcasts. An increase in broadcast traffic can clutter the network, resulting in lag and increasing the probability of packets becoming lost as they travel across the network. Due to this, SMB communications are typically not preferred on networks with a large number of users, where the problem is more likely to become compounded through volume.