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lec14_io0 - Lecture 14 I/O issues and Reliability...

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Lecture 14: I/O issues and Reliability Synchronous I/O – read/write access is blocked until the data buffer is written/read and cleared Asynchronous I/O – read/write operations are done in parallel along with other operations Asynchronous I/O is obviously more desirable (like the difference between sockets or pipes), but keep in mind that the CPU (on a single processor system) still must be time-sliced between the read/write operations and hence are not typically done in parallel. On unix, a hidden disk cache is used for disk output. All systems need an AIO control block, which is a structure that contains the file descriptor, file offset, pointer, byte size, request priority, signal information, and I/O type of operation of the buffer to be received/transmitted. On 68K uprocessors, a DUART is used (Dual Universal Asynchronous Receiver and Transmitter) as a serial port. It contains 7 distinct interrupt level lines, a clock, input/output pins from/to external interface registers, and a transmit and receive line to a RS232 serial port.
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