1. System Environment Part 1 The Register Level

2. Module Content “Systems environment” is a term used to describe the hardware and software structures which allow applications programs like Word, Excel etc. to operate. This module explores this environment in two important respects: 1. The functioning of the microprocessor 2. The working of the Operating System

3. Structure of the Module 1 This module is split into 3 sections, each lasting approximately 4 weeks: Processor Operations at the Register level Processor Operations at the digital logic level Computer Operations at the system software level

4. Structure of the Module 2 Each week there will be two 2-hour sessions: Practical Session (2 Hours) In this session we will look at the exercises and carry out ‘hands-on’ workshop activities. Main Lecture (1 hour) In this session we will look at theory (mainly hardware stuff)

5. Assessment Assessment Comprises: Three in-class tests 60% Week 5: Machine level programs 20% Week 9: Circuit design20% Week 12: Operating Systems20% Two-hour written examination 40%

6. Taking the Lid off the Computer

7. What do we know about computers? 5-minute buzz group activity 1 What do we mean by a computer system? Where do we find such systems?

8. Computers A Computer System means the set of hardware and software components which cause the computer to function. We find theses systems in obvious places like group of boxes on your desktop, but also in less likely places: Cars Washing Machines Microwaves Etc.

9. What else do we know about computers? 10-minute buzz group activity 2 Turn to page 18 in the notes. Can you explain any or all of the terms?

10. Can you put names to… Set of instructions to be executed Program to translate machine level instructions to binary Electronic circuit which can be in one of two states Collection of bi-stable cells representing a binary number Hard-wired program needed to carry out a single CPU instruction Information highway within a computer Number represented by a sequence of 0’s and 1’s Data storage facilityGeneral purpose information processing tool Program which controls computer functionality Electronic circuit which can be in one of two states Number represented by digits 0,1..9 and the letters A,B.. F Measurement of the speed of the CPU Overriding CPU program which checks for input Program which converts language to computer instructions

11. Taking the Lid off Computer Systems In the next few slides we will delve deep into the workings of the computer, using the process of “taking the lid off the box” Each level we encounter will need its own and structures in order to operate effectively.

12. Diagram 1 The HCI Level Computer System User What rules do you know about working at the Human-Computer Interface Level?

13. Human Computer Interaction The quality of interaction between a user and the computer is governed by the standard of design (good or bad) of: The various input/output devices The software interfacing with the user

14. Input and Output Devices 5-minute buzz group activity 3 Turn to Exercise 1 (page 18) in the notes. What are the inputs and outputs of the items named?

15. Diagram 2 The Components Level Main MemorySecondary Memory Central Processing Unit Input DeviceOutput Device User What types of Input device are there? What types of Output device are there?

16. Components Interacting with the CPU The quality of the interaction between the Input/Output devices and the CPU is the remit of the designer of the Operating System What Operating Systems do you know?

17. Diagram 2 The Components Level Main MemorySecondary Memory Central Processing Unit Input DeviceOutput Device User What types of Main Memory are there?

18. Memory Memory is classified into: Random Access Memory (RAM) This is volatile, and information is lost when the computer is switched off. There are two main types: DRAM (cheap, slow) SRAM (faster, expensive) Read –Only Memory (ROM) This retains information even when the computer is switched off Main types are: PROM, EPROM, EEPROM, Flash

19. Diagram 2 The Components Level Main MemorySecondary Memory Central Processing Unit Input DeviceOutput Device User What Sorts of Secondary Memory devices are there?

20. Secondary Memory Storage Information may be stored on these types of devices: Floppy Disks Zip Disks Hard Drive Tape CD DVD etc. Why is the hard drive “secondary” rather than “main” memory?

21. Diagram 3 The CPU Level Central Processing Unit Control UnitRegisters Arithmetic & Logic Unit

22. The Register Level A register is a collection of “cells”. Each cell is a “flip-flop” electronic device which can be in one of two stable states.

23. The Register Level Cells within the register can be held at high or low status. This collection of cells now represents the Binary Number 11011001

24. The Register Level Write Read Information comes in on 8 wires, using a write enable signal. Information is transferred (read) by using a similar read enable signal

25. Diagram 3 The CPU Level Central Processing Unit Control UnitRegisters Arithmetic & Logic Unit

26. Interaction of components within the CPU The quality of the operation of the CPU depends on the design and organisation at the digital electronics level. These elements are etched onto the chip which supports the CPU

27. Diagram 4 The ALU Level Arithmetic & Logic Unit Arithmetic Operations Logic Operations

28. Diagram 5 The Logic Operation Level Logic Operations ANDORNOTCOMPARE

29. Binary and Hexadecimal

30. Bytes The way that information is coded is to use a sequence of zeros and ones It is usual to have a sequence of 8 bits collected together This is called a byte 10110101

31. Bits A bit is the smallest piece of information in the computer In a single cell, the digital information is either One - current is HIGH (ON) Zero -current is LOW (OFF) There are no in-between states ON OFF

32. Bits and Bytes Depending upon the design of the computer, there could be 4, 8 16, 32, 64 (or even more!) bits processed by the computer at once For the next few slides we will look at a simple 4-bit device.

33. A 4-bit register Reading from the right, each bit is worth double the one preceding it. The sequence, reading from the right is: 1,2,4,8,... If we had more bits, it would continue:... 16, 32, 64, etc. 1482 4 is ON 1 is ON

34. Binary Numbers The register shown on the right represents the binary number 0101 This has ones in the 1 and 4 cells, and zeroes in the others. The number represented is 5 1482 41 0101 4+1 = 5

35. Counting in Binary Follow the sequence on the right, and try to continue it. you will see that the switching creates a pattern of ON/OFF in each column 0001 0010 0011 0100 0101 0110

36. Decimal Numbers By decimal, we simply mean that the numbers are written in powers of ten These are 1, 10, 100, 1000, etc. So that: 352 = 300 + 50 + 2 100101 352

37. Binary Numbers By Binary, we mean that numbers are written in powers of two These are 1, 2, 4, 8, 16 etc. So that: 10100 = Which is 16 + 4 = 20 168421 10001

38. Converting Binary to Decimal Example:101101 Reading from right to left the columns are 1,2,4,8 etc. i.e.32168421 101101 So the number in decimal notation is: 32 + 8 + 4 + 1= 45

39. How do we convert Decimal to Binary? There is a specific technique which allows us to do this. It involves repeatedly dividing a number by two and noting the remainder.

40. Converting Decimal to Binary: An example Convert 117 to binary: 117÷ 2 = 58 remainder 1 58 ÷ 2 = 29 remainder 0 29 ÷ 2 = 14 remainder1 14 ÷ 2 = 7 remainder0 7 ÷ 2 = 3 remainder1 3 ÷ 2 = 1 remainder1 1 ÷ 2 = 0 remainder1 In binary the number is: 1110101

41. Adding In Binary Addition in binary is a direct counterpart of operations the processor level. First of all we will look at a numerical example

42. Adding in Binary There are only four possible combinations. The first three are “obvious” The last one is special (remember 1 + 1 = 2, which is 10 in binary) 0 + 0 = 0 0 + 1 = 1 1 + 0 = 1 1 + 1 = 0, carry 1

43. Adding in Binary The answer: 1 0 1 1 1 + 1 1 1 0 1 1 1 0 1 0 0 1 1 1 1 1 1 + 1 = 10 i.e. two in binary 1 + 1 = 10 i.e. two in binary 1 + 1 + 1 = 11 i.e. three in binary 1 + 1 + 1 = 11 i.e. three in binary

44. Other Bases Decimal and Binary are two different number bases used by the computer, but there are others An important one is Hexadecimal which has 16 separate characters: 0,1,2,3,4,5,6,7, 8,9,A,B,C,D,E,F

45. The Hexadecimal System The Hexadecimal number System had 16 separate characters: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F The extra letters are so that the numbers 10-15 can be written using one character each. This means that A7BC is a number written in Hexadecimal code

46. Hexadecimal These numbers are written in base 16, so that a number like 9E means the 9 is 9 x 16 = 144 the E is 14 x 1 = 14 Altogether this would be 158 Dec Hex 0  0 1  1 2  2 3  3 4  4 5  5 6  6 7  7 8  8 9  9 10  A 11  B 12  C 13  D 14  E 15  F

47. Hexadecimal Numbers Normally in the context of computers, we will only be considering two-digit Hexadecimal numbers like A3 or 4E When the numbers have more digits we tend to split them up into two-digit pairs. This makes interpretation a lot easier

48. Hexadecimal to Decimal For example: The number 4E in Hexadecimal, is: 16 1 4 E That is 4 x 16 = 64 and E (= 14) x 1 = 14 Total : 78 (Decimal Notation)

49. Converting Decimal to Hexadecimal Two-digit Hexadecimal numbers lie in the range 0 – 255 We will only consider numbers in this range. The answer will always be a two- digit hexadecimal number

50. Converting Decimal to Hexadecimal Example: Convert 181 to Hexadecimal 187  16 = 11 remainder 5 In Hexadecimal 11 = B In Hexadecimal 5 = 5 This means:181 = B5 DecimalHexadecimal

51. Hexadecimal to Binary The easiest way to convert Hex to Binary is by using a ‘look-up’ table to find the Binary equivalents for the Hex digits 0 to F For example, the Binary for 6A would just be: 6 = 0110 A = 1010 6A = 0110 1010 HexBinary 0 0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001 A 1010 B 1011 C 1100 D 1101 E 1110 F 1111

52. Binary to Hexadecimal Converting Binary to Hex can be done in exactly the same way, by using a look-up table For example the binary number 10011011 will be: 1001 = 9 1011 = B So that 10011011 = 9B Binary Hex 0000  0 0001  1 0010  2 0011  3 0100  4 0101  5 0110  6 0111  7 1000  8 1001  9 1010  A 1011  B 1100  C 1101  D 1110  E 1111  F

53. Adding in Hexadecimal 28 9B C3 1 8 + B = 13 (i.e. nineteen written in hexadecimal) 8 + B = 13 (i.e. nineteen written in hexadecimal) 2 + 9 +1 = C (i.e. twelve written in hexadecimal) 2 + 9 +1 = C (i.e. twelve written in hexadecimal)

54. Activity Now turn to Exercise 2 (page 18) and work through the examples on Binary and Hexadecimal