COP 4600 - Final Exam Study Guide Graded A

What must I/O devices be connected to in order to do anything? - A computer What is a port? - A set of wires that connects an I/O device and the computer. A device that allows other devices to hook up to it in turn is said to support what? - Daisy-chained devices What is a bus? - A common set fo wires used by more than one I/O device If devices connect to ports, what do ports connect to? - Buses What is a controller? - The electronics that manage a port, bus or I/O device What does the operating system actually talk to? - The device's controller What is a data in register? - Allows the computer to get input from the device What is a data out register? - Allows the computer to send output to the device What is a status register? - Indicates the current state of the device, including whether the current command has completed, whether the data registers are ready, and whether there is an error. What is a control register? - A register that is used to send commands to the device What does the interrupt/trap mechanism handle? - User-process calls for I/O, and notifications for those calls. Notifications from hardware about I/O completion, memory exceptions, arithmetic exceptions (divide by zero), and privilege exceptions. What is required in order for direct memory access to work? - Device controllers must be given their own channel to system memory, with its own control registers. What is a device driver? - A piece of software intended to handle interfacing with a particular device's controller. What are some I/O device characteristics? - Stream versus block, sequential versus random, synchronous versus asynchronous, sharable versus dedicated, read/write versus read-only write-only, speed of operation. What are the fundamental functions of block devices? - Read, write, and seek. What are fundamental functions of character-stream devices? - Get and put (often still mapped to read and write with bufferring to allow multiple bytes to be read and written) What is a socket interface? - Provides a file-like metaphor for reading and writing to a network connection What are the three main functions of hardware clocks? - Report the current ime, report the elapsed time, and set an interval timer to report in the future. What are clocks used by the OS for, at a minimum? - To preempt processes, flush cache buffers, and to report the failure of timed-out network connections. What is the device status table? - A table that is used to keep track of each device and related pending request queues. What is a spool? - A special-purpose buffer that serves entire coherent jobs.