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P1. The following figure shows one way of having memory-mapped I/O even in the presence of separate buses for memory and I/O devices, namely, to first try the memory bus and if that fails try the I/O bus. A clever computer science student has thought of an improvement on this idea: try both in parallel, to speed up the process of accessing I, devices. Would this be a good idea, or would it cause any issues? CPU reads and writes of memory go over this high-bandwidth bus CPU Memory I/O This memory port is to allow I/O devices access to memory P2. One mode that some DMA controllers use is to have the device controller send the word to the DMA controller, which then issues a second bus request to write to memory. How can this mode be used to perform memory to memory copy? Discuss any advantage or disadvantage of using this method instead of using the CPU to perform memory to memory copy. P3. A typical printed page of text contains 50 lines of 80 characters each. Imagine that a certain printer can print 6 pages per minute and that the time to write a character to the printer's output register is so short it can be ignored. Does it make sense to run this printer using interrupt-driven I/O if each character printed requires an interrupt that takes 50 sec all-in to service? P4. In which of the four 1/0 software layers is each of the following done. (a) Computing the track, sector, and head for a disk read. (b) Writing commands to the device registers. (c) Checking to see if the user is permitted to use the device. (d) Converting binary integers to ASCII for printing P5. Why are output files for the printer normally spooled on disk before being printed?

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Because of the usage of spooling (temporary directory containing all printing jobs), the users and system can perform other jobs at the same time. More than this, the only process which has access to the physical printer is the special designed daemon and this eliminates the risk of a deadlock for the printer. See last paragraph from pp. 367 and first paragraph from pp. 368....

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