COP4600_14-5-10 - COP 4600 14-5-10 Cochin 14 Administrivia...

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COP 4600 14-5-10 Cochin 14 Administrivia - Read Chapter 1 Operating System Structures Layered Discussion -lowest level communicates directly with the hardware -highest level provides services to application -layers are selected such that each uses the services of each level beneath it (ideally, only directly beneath) *CON: very difficult to define layer ordering because of dependencies -assume the VMem (Virtual Memory) uses a device driver, that would imply it should be at a lower level than the Memory Management system – which is silly. -layered OSen tend to be (slightly) less efficient (due to the overhead of forwarding multiple requests through the layers) -WindowsNT was originally highly layered (because machines were slow by contemporary standards), the layering overhead caused too much of a performance hit; so Microsoft pragmatically adopted a less “formally layered” architecture. Virtual machines & related concepts -it’s said that VMs “take the concept of layering to its logical conclusion:” treats ( hardware + OS kernel ) as hardware Hypervisor Software that allows multiple OSen to run simultaneously on a host -each OS executing on its own VM Paravirtualization the (client) OSen are modified so that systems that interact with the hardware (or otherwise privileged operations) are directed to the
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COP4600_14-5-10 - COP 4600 14-5-10 Cochin 14 Administrivia...

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