Microprocessors

1. Microprocessors Spanning the history to explain the technology

2. Microprocessors • While we call them the “brain” of the computer, they don’t compare to our brain. • We can “wing it” or “make it up as we go” – a processor just stops when confused. • They are really just a very fast calculator, capable of doing the same thing over and over again (code).

3. The Man in the Box • We can (often) think of the processor as a “Black Box.” We need to know what he does, but not how he does it. • Again, the Man in the Box is very good at arithmetic and at following instructions.

4. External Data Bus • First thing to set up is the External Data Bus. • The 8088 had eight wires for the EDB, hence it was considered an 8-bit processor. • Either we (through code) or the processor (results output) “turn on” wire(s) [voltage] so we can communicate.

5. EDB and Binary

6. Inside the CPU • We have registers which are temporary holding places (scratch paper, if you will) for information. • In the 8088, these registers were 16 bits “long” and there were four of them: AX, BX, CX and DX.

7. Code Book

8. The Clock Wire • It “ticks”, or has voltage, to time what goes on with the CPU. • Much like a metronome on top of a piano.

9. Clock Speed • The rated speed of the CPU, measured in Hertz – cycles (ticks) per second. 1 Hz = One cycle per second 1 KHz = One thousand cycles per second 1 MHz = One million cycles per second 1 GHz = One billion cycles per second (also 1000 MHz)

10. Clock Speed • The 8088 had a clock speed of 4.77 MHz, or 4.77 million cycles per second. • It was controlled by a crystal oscillator on the motherboard. • Today, the crystal is built into the processor.

11. Example Clock Crystal

12. Clock Speed • No longer is it the maximum speed the processor can run. • Established by testing the CPU. • CPUs also have a lower limit – they just won’t start at too low a speed. • The System Crystal, or System Clock set the pace for the whole motherboard

14. Machine Language

15. Timing

16. How we get code • Programs are stored on hard disk drive which is too slow to send directly to CPU. • We need a method to store, temporarily, code and get it to CPU as fast as possible. • We will call this method: memory

17. Options • We could use punched cards. • We could use magnetic tape • We do use Random Access Memory (RAM) which gets around the limitations of the other options.

19. Northbridge • Works with the CPU to place RAM contents on the External Data Bus • Also called the Memory Controller Chip • Sits between the processor and memory • Uses the Address Bus to communicate with CPU and Memory

21. Address Bus

22. Address Bus • If we had three wires on our Address Bus, we could come up with eight addresses • The 8088 had twenty wires for 1 million addresses, or 1 MB (1,048,576B)

23. Front Side Bus

24. As we leave the 8088 • Every modern computer starts up as an 8088 • Almost all of the activity in RAM is in the first megabyte • The rest of memory is for data storage

25. Who makes CPUs? • Intel and Advanced Micro Devices (AMD) for the PC • Motorola did for the Apple Mac • For years, Intel and AMD had cross-license agreements – 8088, 286, 386 and 486. • Starting with the Pentium II, Intel and AMD made different chips – requiring different motherboards.

26. What does a CPU look like? • Pin Grid Array (PGA) • Most popular “package” for CPUs • Lots (hundreds) of pins • Usually square in shape • Fragile – pins can bend or break • Land Grid Array (LGA) • Pins are on the motherboard • Processor has “nubs”

29. LGA 775 (Intel)

30. The Socket • Zero Insertion Force (ZIF) socket • Lever up, CPU drops in • Lever down, CPU held in place and good contact on pins

31. SEC • For the Pentium II, Intel tried out a Single Edge Cartridge (SEC) connection method • Intel’s were Slot 1; AMD used Slot A • Early Pentium IIIs also used SEC

34. Using Memory • We need a way to store code and data for the processor • It takes a while to get code/data from RAM • If we get extra, with only a small increase in time, our processor can run longer (hopefully)

35. DRAM and Refresh • Dynamic Random Access Memory • Capacitor and transistor • For a brief time, capacitor acts like a battery – it holds a charge – for about 16 milliseconds • Then, it must be refreshed (recharged) • That’s why it is called Dynamic • DRAM is cheap

36. Cache • It’s cash, not cash-ae • Small amount of really fast memory • Enables us to store code (and data) for the CPU • Disk cache between RAM and hard disk • RAM cache between RAM and CPU • RAM cache allows us to work during refresh cycles

37. Hit and Miss • If we find what we are looking for in cache, that’s a cache hit • If we don’t find what we are looking for in cache, that’s a cache miss and we have to go to RAM or worse, to the hard disk drive.

38. SRAM • Static Random Access Memory • Uses five transistors in FLIP-FLOP circuit, like a light switch • Major expensive, not a lot produced • No refresh required • Almost as fast as CPU

39. L1 and L2 Cache • L1 is small (16-32 KB) and runs almost as fast as CPU. Now is a part of CPU. • L2 cache is larger (64KB to 2MB) and runs slower than CPU. Was external to CPU and now a part of CPU also. • For our next instruction, we go from CPU to L1 cache to L2 cache to RAM

40. Pipelines • More speed – we want to get more done in same amount of time. • Think in terms of laundry, one basket at a time. Sort Wash Dry Fold

41. If we use multiple baskets of laundry, and “fill” the pipeline, we can get much more done, more quickly Sort Wash Dry Fold This is a four stage pipeline. We could add a second Pipeline that included a pre-soak stage for really dirty Laundry.

42. Threads • In our 2+3 example, we had a single thread, or pathway, through the program. • With careful coding and great attention to details, we can write programs that use multiple threads. • Let’s make a pot of coffee as an example:

43. Single thread coffee: Put filter in Put coffee in Put water in Brew Now, let’s get some help and double-thread the process: Put filter in Put coffee in Brew Put water in

44. Clock Speed and Multipliers • Able to build processors that run faster than motherboard • So, we multiply the System Clock to get CPU internal speed • Remember: System Clock is FSB • Example: 100 MHz system times 4.0 multiplier gives 400 MHz internal speed • P4 with 133 FSB and x23 = 3.06 GHz

45. CPU Voltage • Faster processors = more heat • If we reduce CPU voltage, heat output goes down • Use voltage regulators

46. Branch Prediction IF <some condition>, THEN <code for “TRUE” result> ELSE <code for “FALSE” result> END IF If we can see the IF, we can get code from both “sides” Out of order processing and Speculative Execution is running the branch before the test completes. 20

47. Pause here

48. Pentium II • SEC form factor – Slot 1 • End of the cross-licensing with AMD • AMD used Slot A – same shape but different signals on pins – can you say “crispy CPU?” • Faster Pentium Pro with MMX: 233-450 MHz

50. Celeron • Inexpensive Pentium II, no L2 cache at first. • Real poor performance, so introduced 300A with L2 cache. • Could overclock to almost 800 MHz. • Designed to compete against AMD processors.