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351 Operating System

What is DMA Direct Memory Access - used for large data movement
What is blocking I/O? blocking is when a processes is suspended until I/O completed. easy to use and understand but insufficient for some needs
What is asynchronous I/O? process runs while I/O executes
What is buffering? store data in memory while transferring between devices (1)To cope with device speed mismatch (2)To cope with device transfer size mismatch (3)To maintain “copy semantics”
What is caching? faster device holding copy of data Always just a copy Key to performance Sometimes combined with buffering
What is the difference between buffering and caching?
What is stream?
How to improve performance of a computer system? (I/O)
What is non-blocking I/O? I/O call returns as much as available. user interface, data copy(buffered I/O) implemented via multi-threading, returns quickly with count of bytes read or written, select() to find if data ready then read() or write() to transfer
Double buffering (1) two copies of the data, Kernel and user (2) Varying sizes, Full / being processed and not-full / being used (3)Copy-on-write can be used for efficiency in some cases