The second generation of computers, spanning from the late 1950s to the mid-1960s, is defined by the invention and use of the transistor. Transistors replaced the large, power-hungry, and unreliable vacuum tubes used in first-generation machines. This technological shift resulted in computers that were significantly smaller, faster, cheaper, more energy-efficient, and more reliable than their predecessors. The use of transistors was a pivotal development that paved the way for more complex and accessible computing systems.

A. First generation: These computers were characterized by the use of vacuum tubes for circuitry and magnetic drums for memory, not transistors.

C. Third generation: This era was defined by the development of the integrated circuit (IC), which placed many transistors onto a single silicon chip.

D. Fourth generation: This generation is marked by the microprocessor, which integrates the entire central processing unit (CPU) onto a single integrated circuit.

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1. Patterson, D. A., & Hennessy, J. L. (2017). Computer Organization and Design: The Hardware/Software Interface (5th ed.). Morgan Kaufmann.

Reference: Appendix B, Section B.2, "A Brief History of Computers," describes the second generation (1955–1965) as being built with transistors, which replaced vacuum tubes.

2. Stallings, W. (2016). Computer Organization and Architecture: Designing for Performance (10th ed.). Pearson.

Reference: Chapter 2, Section 2.1, "A Brief History of Computers," subsection "The Second Generation: Transistors." This section explicitly states, "The first major change in the electronic computer came with the replacement of the vacuum tube by the transistor... The transistor is smaller, cheaper, and dissipates less heat than a vacuum tube but can be used in the same way."

3. Ceruzzi, P. E. (2012). Computing: A Concise History. MIT Press.

Reference: Chapter 3, "The Transistor and the Integrated Circuit," pp. 59-62. This chapter details the invention of the transistor at Bell Labs and its application in computers, marking the transition to the second generation.

4. Null, L., & Lobur, J. (2015). The Essentials of Computer Organization and Architecture (4th ed.). Jones & Bartlett Learning.

Reference: Chapter 1, Section 1.4, "The Generations of Computing." The text specifies that the second generation of computers used transistors as the main component for processing.