1. MARIE:An Introduction to a Simple Computer Michael Dougherty 4.1 - 4.5 September 17, 2009

2. Central Processing Unit CPU Fetches Program Instructions Decode Each Instruction Perform Operation Divided into two parts Datapath Control Unit

3. Datapath Registers ALUs Buses Clock

4. Registers D Flip-Flops can be used as registers A clock pulse controls access to the data

5. Registers Registers have a fixed “word” size Number of registers are usually a power of 2 Special Purpose

7. ALU Performs the operations such as comparisons, adding, and multiplying Generally has two data inputs and one data output These operations often affect bits in the status register

8. A Simple ALU circuit

9. Control Unit Sequences operations Ensures data is at the correct place at the correct time

10. The BUS The wires that connect the CPU to other components Only one item at a time can use the bus Speed is affected by length and number of devices sharing it.

11. Point-to-point bus Point-to-point bus connects two specific devices

12. Common pathway Common pathway connects a number of devices “Multipoint” bus

13. Bus Protocol Data bus Control lines Address lines Power lines

14. Data Bus Data bus - the actual information to move from one location to another

15. Control lines Control lines - tell which device has permission to use the bus and for what.

16. Address lines Address lines - the location in memory that the data should be read from or written to.

17. Power lines Power lines - provides the power to the circuitry.

18. Bus Types Processor-memory Buses I/O Buses Backplane Bus Personal Computer Buses Internal Bus (System Bus) External Bus Local Bus

19. Just Some Wires? Synchronous buses

20. Asynchronous buses Handshaking Protocol ReqREAD ReadyDATA ACK

21. Bus arbitration Daisy Chain Arbitration Centralized Parallel Arbitration Distributed Arbitration using self-selection Distributed arbitration using collision detection

22. Clocks Speed Clock cycles Clock Frequencies (MHz or GHz) Clock Cycle Time Bus clocks Overclocking

23. Speed vs. Performance Same clock speed ≠ same performance Intel 286 Pentium

24. Overclocking Pushes manufacturer’s time constraints

25. The I/O Subsystem Most familiar items of computer Not connected directly to the CPU Memory-mapped I/O

26. Instruction-based I/O No memory use Limited CPUs can use devices