Answers for Homework 2

1. No I/O devices to input data and output results.
   
   
2. It is possible to use a software-based solution for such a protection scheme.
   You can develop a program to implement such function and add this function into the operating system. Every time you access a memory, the OS will check whether it is unauthorized. The disadvantage of such implementation is that the system will switch between user mode and kernel mode frequently. The running of checking program will also occupy the CPU time of a user program. All these lower the efficiency of the system greatly.
   
   
3. Interrupt is an asynchronous event caused by peripheral devices. It is manly implemented by hardware, So it won’t occupy the CPU time and consume system resources. Only when an interrupt happened, CPU stops what it is doing and spends a little time on it.
   
   The alternative is polling, That means the OS will check every device frequently. This will consume a lot of CPU time and reduce the efficiency greatly.
   
   
4. The cache between CPU and main memory. The cache between CPU and peripheral device.
   The cache speeds up the memory access time greatly.
   The disadvantage is the limit size and high price.
   
   
5. (1) large space
   (2) low price

NOTE: The answer is just for reference. If you have any question about it, please email me at nxz5371@megahertz.njit.edu