are you sure it's only used for installation.
My college computer center has a lab where all computers have very few hardware resources (small ram, no harddisk, one lan card) attached to them and are connected to a central processor.
(forgot the exact term for these kind of systems)
They too boot from LAN .. from the central servers using similar pre-boot exection environment.
Dont they too use this feature of lan card ?? or it's something different ?
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alibi