# Disks like the one described in the example on page

• Homework Help
• 7
• 100% (11) 11 out of 11 people found this document helpful

This preview shows page 5 - 7 out of 7 pages.

disks like the one described in the example on page 570. If the I/O is allowed to consume 100% of the bus and memory bandwidth, what is the maximum number of simultaneous disk transfers that can be sustained for the two block sizes?
P11. (5 point) We want to compare the maximum bandwidth for a synchronous and an asynchronous bus. The synchronous bus has a clock cycle time of 50 ns, and each bus transmission takes 1 clock cycle. The asynchronous bus requires 40 ns per handshake. The data portion of both buses is 32 bits wide. Find the bandwidth for each bus when performing one- word reads from a 200-ns memory.
4bytes/360ns=11.1MB/sec Accordingly, the synchronous bus is only about 20% faster. Of course, to sustain these rates, the device and memory system on the asynchronous bus will need to be fairly fast to accomplish each handshaking step in 40ns. P12. (5 point) Let’s determine the impact of polling overhead for three different devices. Assume that the number of clock cycles for a polling operation – including transferring to the polling routine, accessing the device, and restarting the user program – is 400 and that the processor executes with a 500 MHz clock. Determine the fraction of CPU time consumed for the following three cases, assuming that you poll often enough so that no data is ever lost and assuming that the devices are potentially always busy:
6