Daisy chain (information technology)
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Daisy chain is a term used in information technology.
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[edit] Computer software
The term is also used in computer software. Daisy chain installation is a "smart" installation, whereby an installation can happen piecemeal, as all the components of the package are connected to each other. If there is a disconnect during a web-based installation the software need not be downloaded from scratch, but rather restarted from where it stopped. Eg: the installation of Google Pack.
[edit] Computer hardware
The term is also used when connecting multiple hardware using the same communication protocol to a shared communication bus. For example when you connect multiple hardware having UART ports which communicate via RS-232 protocol to the same physical bus, you are making a daisy chain. This means that you wire all RX signals together and all TX signals together and so on. Then a predefined logic would allow only one of them to seize the bus in a given time. This way you say that your devices are daisy chained. Some other situations or protocols which use daisy chains are SCSI and Firewire devices.
[edit] Network topology
See Network topology#Daisy chain.
[edit] System access
The term is also used in the context of the Session-, Application- or Presentation Layer when a computer system is not being accessed directly but rather by deliberately hopping via other systems first. In the easiest example, a telnet or SSH connection is established from the first machine to the shell on a second machine, and then from the second machine to the shell on a third machine. Another typical example is the "terminal session inside a terminal session" using RDP. There are many reasons to create such types of daisy chains, such as to connect to a system on a non-routed network via one or more gateway systems, keeping sessions alive on a main computer while not being connected to this main computer at all times, to save bandwidth or when on an unstable network by first connecting to a better connected machine, or even in an attempt to cover one's tracks while engaged in cybercrime.
