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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.
- Spring '14