现代操作系统第三版课后答案16章.docVIP

SOLUTIONS TO CHAPTER 1 PROBLEMS 1. An operating system must provide the users with an extended (i.e., virtual) machine, and it must manage the I/O devices and other system resources. 2. Multiprogramming is the rapid switching of the CPU between multiple processes in memory. It is commonly used to keep the CPU busy while one or more processes are doing I/O. 3. Input spooling is the technique of reading in jobs, for example, from cards, onto the disk, so that when the currently executing processes are ?nished, there will be work waiting for the CPU. Output spooling consists of ?rst copying printable ?les to disk before printing them, rather than printing directly as the output is generated. Input spooling on a personal computer is not very likely, but output spooling is. 4. The prime reason for multiprogramming is to give the CPU something to do while waiting for I/O to complete. If there is no DMA, the CPU is fully occupied doing I/O, so there is nothing to be gained (at least in terms of CPU utilization) by multiprogramming. No matter how much I/O a program does, the CPU will be 100 percent busy. This of course assumes the major delay is the wait while data are copied. A CPU could do other work if the I/O were slow for other reasons (arriving on a serial line, for instance). 5. Second generation computers did not have the necessary hardware to protect the operating system from malicious user programs. 6. It is still alive. For example, Intel makes Pentium I, II, and III, and 4 CPUs with a variety of different properties including speed and power consumption. All of these machines are architecturally compatible. They differ only in price and performance, which is the essence of the family idea. 7. A 25 ×?80 character monochrome text screen requires a 2000-byte buffer. The 1024 ×?768 pixel 24-bit color bitmap requires 2,359,296 bytes. In 1980 these two options would have cost $10 and $11,520, respectively. For current prices, check on how much RAM currently costs, pro