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There is a common misconseption that read()/write() system calls block users until physical IO to disk is completed.
read()/write() system calls do not block users during pyhsical IO unless file is opened with O_DIRECT or O_SYNC flags. Users are blocked just during copying buffers from/to user address space to/from kernel address space. So, although read()/write() calls look synchronous in user perspective, they don't do physical IO as synchronously.
In Asynchronous IO calls(i.e aio_read()/aio_write()), users are just blocked during enqueuing IO requests, not during copying buffers from/to user address space to/from kernel address space and not during physical IO.
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