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Computer Architecture Prof. Anshul Kumar Department of Computer Science and Engineering Indian Institute of Technology, Delhi Lecture - 2 History of Computers In the previous lecture I talked about what is important in this course what we are going to cover in this course and in this lecture I am going to look at history of computers. History is important because by studying history we get good insight into the subject whether it is political history, economic history or history of science or history of computers and we get to know the present better as well as the future better. So we look at the developments which have taken place in the past, which have made significant impact on the computer we see today and we are going to see tomorrow. First of all we will look at the past, half a century or so and see how this period gets divided into different generations then we will look at what had been the landmark developments which have had significant impact on history or on the design and architecture. (Refer Slide Time: 01:49) We will look at some of the interesting old pictures of computers and finally have a look at briefly, as mentioned, what technology is being worked upon in various research labs and they may decide what kind of computers they are going to have in the future.

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(Refer Slide Time: 02:35) This period of about half century or so is divided into five generations. There may be some differences of opinion here. Some people recognize only four generations but some talk of five so I will talk of all the five and mention which one is the fifth one which is not a regular generation as recognized by many people. These different generations as we see are predominantly different in terms of the technology which is used to develop computer systems or electronic system in general. As some major technological development takes place everything changes; a very significant, very drastic sudden change in the shape of the things and it gives rise to a new generation. These changes the fundamental changes are in terms of size, size of computers. As I mentioned last time that what is to be a room full has not shrunk on to something small which can come on desktop. In terms of cost, the affordability has been changed over time. Earlier computer used to be affordable by large organizations, now large number of people can afford to have the individual computers and in fact if you count all embedded computers the computer density in many cases may be more than one per person if you look at all devices, all appliances, mobile phones and various equipment the number of computers you have you can account for per person could be even more than one that is the situation today. The power consumption has changed drastically by several orders of magnitude, the efficiency in terms of performance what they could do for a given input that has changed and of course reliability. There was a situation when every now and then something will go wrong and has to be taken care of but now computers can work very reliably for extended periods.

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(Refer Slide Time: 04:55) The beginning in 40's so 40's to 50's is what is considered as the first generation where the basic device was vacuum tube. The vacuum tube is the bulb like device as you can see in the picture here it is a basic electronic device which can amplify signals or it can switch voltage at current levels. So this is expensive, bulky, unreliable and power guzzlers. The computer is built using this where it is again huge, roomful of system and the input output devices were punched cards and paper tapes. The memory was in the form of a rotating drum, magnetic rotating drum and the language used to program was machine language so this was how the first generation computers were. (Refer Slide Time: 05:55)

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The second generation as you would notice a period which I am indicating are overlapping it is not that suddenly on day one the generation ends and next one starts so there is a transition but when there is a change there is a rapid transition otherwise all the time there is growth, development, improvement but a generation change is marked by not absolutely abrupt but rapid transition. So, that change here occurred with the arrival of transistor. So the picture shows some old transistor from Texas Instruments. These transistors performed roughly similar functions what the vacuum tube did but they were much smaller, faster, cheaper and more efficient in terms of energy; also reliability was much better in terms of the time after which the transistor is likely to fail. There was also further development in terms of software; instead of machine language people started using assembly language and also within this period some languages high level languages their early versions they appeared such as FORTRAN and COBOL. (Refer Slide Time: 07:13) Then the technology moved further, it became possible to put several transistors together on a single silicon chip that was called integrated circuits. So you can integrate many transistors and that appears as a single device. The picture here shows the layout of some early chip. Depending upon the level of integration these were characterized as SSI, MSI or LSI. SSI stands for Small Scale Integration, Medium Scale Integration and Large Scale Integration or small scale integration would mean may be a few devices few transistors may be about ten, fifteen or so; medium scale integration would take to a few tens of transistors and large scale would scale few thousands of transistors. So with this naturally the equipment computer became more compact, the speed increased, the efficiency increased, additional peripherals became available, the computing became more interactive; with cards and paper tape it was a batch processing environment entirely that is you submit your program for running and a day later or two days later depending upon the load and efficiency of the system you will get your results. So it is not that you press a button and immediately see the results; you will have to prepare a deck of cards on which

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