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42U, 42 Unit
Blade servers are self-contained computer servers, designed for high density. more...
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Whereas a standard rack-mount server can exist with (at least) a power cord and network cable, blade servers have many components removed for space, power and other considerations while still having all the functional components to be considered a computer. A blade enclosure provides services such as power, cooling, networking, various interconnects and management - though different blade providers have differing principles around what should and should not be included in the blade itself (and sometimes in the enclosure altogether). Together these form the blade system.
In a standard server-rack configuration, 1U (one rack unit, 19" wide and 1.75" tall) is the minimum possible size of any equipment. The principal benefit of, and the reason behind the push towards, blade computing is that components are no longer restricted to these minimum size requirements. The most common computer rack form-factor being 42U high, this limits the number of discrete computer devices directly mounted in a rack to 42 components. Blades do not have this limitation; densities of 100 computers per rack and more are achievable with the current generation of blade systems.
Server blade
In the purest definition of computing (a Turing machine, simplified here), a computer requires only;
memory to read input commands and data;
a processor to perform commands manipulating that data, and;
memory to store the results.;
Today (contrast with the first general-purpose computer) these are implemented as electrical components requiring (DC) power, and in operation produce heat. Other components such as hard drives, power supplies, storage and network connections, basic IO (such as Keyboard, Video and Mouse and serial) etc. only support the basic computing function, yet add bulk, heat and complexity, not to mention moving parts that are more prone to failure than solid-state components.
In practice, these components are all required if the computer is to perform real-world work. In the blade paradigm, most of these functions are removed from the blade computer, being either provided by the blade enclosure (e.g. DC power supply), virtualised (e.g. iSCSI storage, remote console over IP) or discarded entirely (e.g. serial ports). The blade itself becomes vastly simpler, hence smaller and (in theory) cheaper to manufacture.
Blade enclosure
The enclosure (or chassis) performs many of the non-core computing services found in most computers. Non-blade computers require components that are bulky, hot and space-inefficient, and duplicated across many computers that may or may not be performing at capacity. By locating these services in one place and sharing them between the blade computers, the overall utilisation is more efficient. The specifics of which services are provided and how vary by vendor.
Read more at Wikipedia.org
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