Question

You use a 1 GHz system with paged virtual memory for doing a real-time application. No other application is running on the system. A real time application is one where each task should be finished within a guaranteed time bound. In this particular real-time application, there are many tasks; each runs exact same code except with different data each time. Each real-time task reads 20 bytes from an I/O device, does some processing on it, and writes updated 20 bytes of data back to I/O device. I/O reads or writes are performed at 20 MB/sec. The code to process 20 bytes has a total of 10 loads and stores, and takes 10000 cycles while all memory accesses are cache hits. These loads and stores can access wherever in virtual memory. System transfers control to another task with an overhead of 1000 cycles.

Every memory access takes 25 ns and each disk page transfer from virtual memory swap space takes up to 2 ms. In the worst case a load or store might require 4 memory accesses and 2 disk transfers. How many real-time tasks be able to be guaranteed to run on this system per second in worst case?