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  1. Consider sending a large file of 360,000 bits from Host A to Host B, connected through a router, as shown in the below figure. Assume that there is no queuing ans propagation delay, and the router has sufficient buffer space. Host A splits the file into segments of $S$ bits each and adds 36 bits of header to each segment, forming packets of $(36+S)$ bits. Each link has a transmission rate of $R$ bps. Find the value of $S$ that minimizes the time needed to move the file from Host A to Host B
  2. The CPU of a system having an execution rate of 1 million instructions per second needs 4 machine cycles on an average for executing an instruction. On an average, 50% of the cycles use memory bus. For execution of the programs, the system utilizes 90% of the CPU time. For block data transfer, an I/O device is attached to the system, while the CPU executes background programs continuously. Determine the maximum I/O transfer rate for each of the two cases: 
    1. programmed I/O
    2. cycle-stealing DMA (in transparent mode)

You may assume that transferring one byte involves 4 operations: in-status, check-status, branch and read/write in memory, each requiring one machine cycle.

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