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# Assignment 1
This assignment should be submitted after you have finished Unit 1. It is worth 10% of your final grade.
## Part 1: Concepts and Principles (60 marks; 5 marks each)
Instructions: Please answer the following questions in complete sentences. Your answer for each question should be about 150 words.
1. Define the concepts interrupt and trap, and explain the purpose of an interrupt vector.
An interrupt vector is a list or table of interrupts. Each interrupt has an
address to the interrupt routine to execute when the interrupt is signaled.
A trap is a way to capture a triggered signal to allow programs to respond to
and handle the signal.
Signals can be sent to a particular process via the `kill` program.
A list of signals that can be sent are listed below:
```bash
モ kill -L
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
```
Programs can also trap a signal and handle them. In the following example
the Ruby program is trapping the `SIGUSR1` signal to reload a configuration
file.
```ruby
#!/usr/bin/env ruby
pid = fork do
Signal.trap("USR1") do
puts "done"
exit 0
end
loop do
print "."
sleep 1
end
end
Process.detach(pid)
sleep 5
Process.kill("USR1", pid)
```
When this program is run it will print a '.' 5 times and then exit.
```bash
モ ruby lib/sigtrap.rb
.....done
```
1. How does a computer system with von Neumann architecture execute an instruction?
* fetch instruction from memory and store that instruction in the instruction register.
* decode instruction. may cause operands to be fetched from memory and stored in some internal register.
* execute instruction
* store result back in register
```plaintext
-------------
| --------- |
| | CPU | |
| | ----- | |
| | |CU | | |
| | ----- | |
---------- | | ----- | | ----------
| Input | | | |ALU| | | ----> | Output |
| Device |----> | | ----- | | | Device |
---------- | --------- | ----------
| | A |
| V | |
| --------- |
| | MU | |
| --------- |
-------------
CPU: Central Processing Unit
CU: Control Unit
ALU: Arithmetic/Logic Unit
MU: Memory Unit
```
[source][wiki-von-neumann]
1. What role do device controllers and device drivers play in a computer system?
Each device controller is in charge of a specific type of device.
The device controller is responsible for moving the data between the peripheral
devices that it controls and its local buffer storage.
Operating systems have a device driver for each device controller. This
device driver understands the device controller and presents a uniform
interface to the device to the rest of the operating system.
To start an I/O operation, the device driver loads the appropriate registers
within the device controller. The device controller, in turn, examines the
contents of these registers to determine what action to take. The controller
starts the transfer of data from the device to its local buffer. Once
the transfer of data is complete, the device controller informs the device
driver via an interrupt that it has finished its operation. The device
driver then returns control to the operating system, possibly returning
the data or a pointer to the data if the operation was a read. For
other operations, the device driver returns status information.
1. Why do clustered systems provide what is considered high-availability service?
1. Describe an operating system’s two modes of operation.
1. Define cache, and explain cache coherency.
1. Describe why direct memory access (DMA) is considered an efficient mechanism for performing I/O.
1. Describe why multicore processing is more efficient than placing each processor on its own chip.
1. Describe the relationship between an API, the system-call interface, and the operating system.
1. Describe some requirements and goals to consider when designing an operating system.
1. Explain why a modular kernel may be the best of the current operating system design techniques.
1. Distinguish between virtualization and simulation.
## Part 2: Design Considerations (40 marks)
Instructions: Please answer the following questions in about 1-2 pages each.
1. Draw a typical computer organization figure that includes the main components of von Neumann architecture. Identify each component, and explain its function and interaction relative to other components. (15 marks)
1. Define system call, and list the main types of system calls. Elaborate on how a system call interacts with a standard C library and hardware under a dual-mode operating system environment. (10 marks)
1. Describe the overall structure of virtual machines, and compare VMware and JVM. (15 marks)
[wiki-von-neumann]: https://en.wikipedia.org/wiki/Von_Neumann_architecture
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