5 Problems with Disk Drives, Interrupt Requests, and I/O

1. A 32-bit computer has two selector channels and one multiplexor channel. Each selector channel supports two magnetic disk and two magnetic tape units. The multiplexor channel has two line printers, two card readers, and ten VDT terminals connected to it. Assume the following transfer rates.
Disk drive                      700 Kbytes/s
Magnetic tape drive      200 Kbytes
Line printer                   6.6 Kbytes/s
Card Reader                1.2 Kbytes/s
VDT                               1 Kbytes/s
Estimate the maximum aggregate I/O transfer rate in this system.

2. Given the following set of events, show which routines the CPU is executing for times 0 to 100 ns. Each handler routine (with its interrupt request) takes 20 ns to complete. The priority of the interrupts ranges from IRQ6 as the highest priority interrupt to IRQ0 as the lowest priority interrupt.
Time          Action
0 ns          Start of main program
10 ns         IRQ2
25 ns         IRQ5
40 ns         IRQ6
50 ns         IRQ1

Time      Action
0 ns:      Start of Main Program
10 ns:    IRQ2

3. If an address bus needs to be able to address four devices, how many conductors will be required?
What if each of those devices also needs to be able to talk back to the I/O control device?

4. Define the terms seek time, rotational delay, and transfer time. Explain their relationship.

5. Suppose a disk drive has the following characteristics:
- 5 surfaces
- 512 tracks per surface
- 128 sectors per track
- 1024 bytes per sector
- Track-to-track seek time of 12 milliseconds
- Rotational speed of 1500 RPM
a) What is the capacity of the drive?
b) What is the access time?

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1) The maximum aggregate I/O transfer rate of the system is equal to:
700Kbystes/s + 700 Kbytes/s+ 2* 6.6 Kbytes/s+ 2* 1.2 Kbytes/s+ 10* 1Kbytes/s = 1,400 Kbytes/s+ 13.2 Kbytes/s+ 2.4 Kbytes/s+ 10 Kbytes/s= 1,425.6 Kbytes/s....