1. Suppose that a certain program takes 200 seconds of elapsed time to execute. Out of these 200 seconds, 180 seconds is the CPU time and the rest is I/O time. If the CPU performance improves by 40% every year for the next seven years because of developments in technology, but the I/O performance stays the same then

2. Review

3. CS501 Advanced Computer Architecture
Lecture23
Dr.Noor Muhammad Sheikh

4. Elapsed time = CPU time + I/O time
the I/O time = 200 – 180 = 20 sec
which is 10 % of the elapsed time.

5. Year #
CPU
Time
I/O
Elapsed
...I/O Time..
Elapsed Time
180 20
200
10 % 1
129
149
13.42 % 2 92
112
17.85 % 3 66 86
23.25 % 4 47 67
29.85 % 5 34 54
37.03 % 6 24 44
45.45 % 7 17 37
54.05 %

9. For Pentium processor, the I/O devices are mapped on the I/O space.
For SRC, there is no separate I/O space.
Some address space out of the memory address space is used to map I/O devices in SRC.

10. Advantages of Memory Mapped I/O
All the instructions which access memory can be used for I/O devices.
No need for including separate I/O instructions in the ISA of the processor.

11. Disadvantages of Memory Mapped I/O
The I/O interface will become complex.
If partial decoding is used to reduce the complexity of the I/O interface, then a lot of memory addresses will be consumed.

17. The waveforms correspond to a “read” operation.
A similar explanation is applied to a “write” operation.
The latching of the incoming data can be done by the master either by using the rising edge of the Enable signal or by using its falling-edge.

18. Framing Error
Parity Error
Overrun Error
Underrun Error

19. Framing Error
A 0 is received instead of a stop bit (which is always a 1).

20. Parity Error
The parity of the received data is not the same as it should be.

21. Overrun Error
The prior character that was received, was not still read by the CPU and is over written by a new received character.

22. Underrun Error
No character is available at the beginning of an interval.

23. Block diagram of a modern general purpose digital computer
Computer bus or
system bus
Now we want to focus on what a computer is.
The speaker may explain the building blocks in this slide
The bus interface unit is usually between the CPU and the system.

24. PROCESSOR EXTERNAL BUS
I/O Sub System
HARD DISK
CPU
PROCESSOR EXTERNAL BUS
BUS
INTERFACE
UNIT
CD-ROM
MEMORY BUS
VIDEO CARD
MONITOR
MEMORY SYSTEM
I/O BUS

25. Examples of I/O buses :
The PCI bus
The ISA bus

26. I/O buses provide an “abstract interface”.
By standardizing the I/O buses, as done by several agencies, the third party manufacturers can build add-on sub systems for existing architectures.
The location of these I/O buses may be different in different computers.

27. Earlier generation computers used a single bus to communicate with the memory as well as the I/O devices.
This causes the bandwidth of the bus to shared between the memory and I/O devices.

28. Now-a-days ,the computers have separate memory and I/O buses.
This situation gives more flexibility to users wanting to upgrade their existing systems.

29. Disadvantages of I/O Buses
Every bus has a fixed bandwidth.
Electrical constraints further reduce the bandwidth .

30. Problem Statement: What will be the implications?
Consider an I/O bus that can transfer 4 bytes of data in one bus cycle. Suppose that a designer is considering to attach the following two components to this bus:
Hard drive, with a transfer rate of
40MBytes/sec.
Video card, with a transfer rate of 128MBytes/sec.
What will be the implications?

31. The maximum frequency of the bus is 30 MHz.
The maximum bandwidth = 30 x 4
of this bus
= 120Mbytes/sec.
The demand for
bandwidth of these =
two components
= 168Mbytes/sec

32. Conclusion:
168MBytes is more than the 120 Mbytes/sec that the bus can provide.
One or both of these components will operate at reduced bandwidth.

33. Bus Arbitration