In a multitasking environment : what is a timeslice (quantum)? what is a context switch? When a large number of processes (jobs) are multitasking the actual length of time spent on each process is determined by the O/S specifications, and the term that is often used to describe it is the ‘quantum’ or a timeslice. The actual changeover of the CPU executing one job and changing over to another is generally referred to as context switch. In a multitasking environment : what is a timeslice (quantum)? what is a context switch? When a large number of processes (jobs) are multitasking the actual length of time spent on each process is determined by the O/S specifications, and the term that is often used to describe it is the ‘quantum’ or a timeslice. The actual changeover of the CPU executing one job and changing over to another is generally referred to as context switch.

What is a timeslicing scheduling policy? A time slicing scheduling policy relies on the O/S allocating each job a predefined time slice (Quantum) which is typically 1ms-10ms. Processes are assigned this quantum which must not be exceeded. As soon as the time quantum has been reached, an interrupt occurs and the executing process is placed at the back of the FIFO queue. A hardware timer that generates an interrupt at pre-set intervals usually provides the time quantum. This policy is pre-emptive which only occurs at expiry of quantum time.

For an 8-bit ISA I/O bus, running at the speed of 8.3MHz calculate the following: Bandwidth of the bus. The amount of time it would take to transfer 4Mbytes of raw data on this I/O bus. Calculate the amount of time it would take to transfer 4Mbytes of raw data on a 64-bit, FSB running at 333MHz.

The file and print server on your network has an I/ O bus which is 16-bits wide, operating at 66MHz. How long would it take to transfer 200MBytes of print data (i.e. single job) on this bus? If you have 50 users connecting to the file server and each of these is transferring 50Mbytes of data (i.e. 50 separate jobs). How long would it take for each of these jobs to complete? How long would each job have to wait in this sequence of 50 jobs?

Compare how scheduling jobs sequentially on a FCFS basis and scheduling each job using a 10mS timeslice figure on the Quality of service to the user. Explain with justification the scheduling policy that you would recommend in order to manage the above data transfer on the server I/O bus. If the context switching time is 50 micro seconds, calculate the amount of time that it would take to complete all the jobs identified above for each scheduling policy.