2a was a fragile glass device that used filaments as

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Unformatted text preview: re built by using thousands of vacuum tubes. A vacuum tube [see Figure 1.2(a)] was a fragile glass device that used filaments as a source of electrons and could control and amplify electronic signals. It was the only high-speed electronic switching device available in those days. These vacuum tube computers could perform computations in milliseconds and were referred to as first-generation computers. We also saw that the concept of stored program and the idea of storing both instructions and data in the binary form were introduced in 1946. Hence most of the first-generation computers worked on the principle of storing program instructions along with the data in the memory of the computer so that they could automatically execute a program without human intervention. The memory of these computers was constructed using electromagnetic relays and all data and instructions were fed into the system from punched cards. Of course, the instructions were written in machine and assembly languages because high-level programming languages were introduced much later (computer languages are covered in Chapter 12). Even assembly language was invented in early fifties, so the first-generation computers of 1940s were programmed in machine language only. Only the first-generation computers introduced later such as UNIVAC I and IBM 701 could be programmed in assembly language. Because machine and assembly languages are very difficult to work with, only a few spets understood how to program these early computers. Moreover, the concept of operating system (discussed in Chapter 14) was also not there during the era of first-generation computers. Hence, the first-generation computers were largely usable only by good electronics engineers who understood the logical structure of a computer in great detail and also knew machine and assembly language programming. The characteristic features of first-generation computers are as follows: 1. They were the fastest calculating devices of their time...
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This document was uploaded on 04/07/2014.

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