Second generation of computers, Transistors (1956-1963)

Second generation of computers, Transistors (1956-1963). The second generation of computers refers to the period in the history of computing that took place from the late 1950s to the mid-1960s. This era was characterized by significant advances in computer technology, including the use of transistors as electronic components, which replaced the vacuum tubes used in the first generation of computers.


Here are some key features of the second generation of computers:

  • Transistors: The development and widespread use of transistors, which are smaller, more reliable and more energy efficient than vacuum tubes, was a breakthrough in computer technology during the second generation. Transistors allowed computers to be smaller, faster and more reliable, which increased their processing power and improved their performance.
  • Smaller size: Compared to the first generation of computers, which were often huge and filled rooms, the computers of the second generation were much smaller. Transistors made it possible to build more compact computers, suitable for use in business, research and other environments.
  • High-level programming languages: During the second generation, high-level programming languages such as FORTRAN, COBOL, and ALGOL were developed, making it easier for programmers to write complex software code. This led to the development of more sophisticated software applications and paved the way for the flourishing of the software industry.
  • Magnetic core memory: The second generation of computers also saw the use of magnetic core memory, a form of random access memory (RAM) that used small magnetic cores to store data. Magnetic core memory was faster and more reliable than previous forms of memory, such as drum memory, and allowed computers to store larger amounts of data.
  • Batch processing: Second-generation computers were often used for batch processing, in which jobs were batched and processed sequentially. This allowed a more efficient use of computing resources and increased productivity in data processing tasks.
  • Limited commercial availability: While the first generation of computers was mainly used in scientific and research environments, in the second generation its commercial availability increased. Computer manufacturers began selling computers to businesses, government agencies, and other organizations, leading to increased adoption and use of computers in various industries.
  • Some examples of second-generation computers are the IBM 1620 series. These computers represented significant advances in computer technology and laid the foundation for future developments in later generations of computers.


Transistors are semiconductor devices widely used in electronic circuits to amplify and switch electronic signals. They were invented in late 1947 by physicists John Bardeen, Walter Brattain and William Shockley at Bell Laboratories in the United States.

His work was based on previous research on semiconductor materials and aimed to find an alternative to vacuum tubes, which were bulky, brittle and inefficient.

The first transistor was made of germanium, a semiconductor material, and consisted of three layers (hence the name “transistor”, derived from “transfer resistance”). It was a solid-state device that could amplify and switch electronic signals without the need for bulky vacuum tubes.
The invention of the transistor was a pivotal moment in the history of electronics, as it laid the foundation for the development of modern electronic devices, such as computers, televisions, radios, and mobile phones.

The world would see transistors replace vacuum tubes in the second generation of computers. The transistor was invented at Bell Labs in 1947, but did not come into widespread use in computers until the late fifties.

Transistors Vs vacuum tubes

Transistors and vacuum tubes are electronic devices used to amplify and switch electronic signals, but they differ in several key respects. Here are some comparisons between transistors and vacuum tubes:

  • Size and form factor: Transistors are solid-state devices and are typically much smaller in size than vacuum tubes. They are made of semiconductor materials and are usually encapsulated in small packages. Vacuum tubes, on the other hand, are bulky and larger, as they need a vacuum-sealed glass envelope to function.
  • Power consumption: Transistors typically consume much less power than vacuum tubes. Vacuum tubes require high voltages to operate and can consume a lot of power, while transistors are usually low-voltage devices and are more energy efficient.
  • Reliability: Transistors are known for their high reliability and long service life, as they have no moving parts and are not affected by mechanical wear. In contrast, vacuum tubes are more likely to break down due to their delicate glass envelope, high operating voltages and the heat generated during operation.
  • Switching speed and characteristics: Transistors have much faster switching speeds than vacuum tubes, making them ideal for high-frequency applications such as digital logic circuits and microprocessors. Vacuum tubes are relatively slower and may not be suitable for high-speed applications.
  • Heat dissipation: Vacuum tubes generate a significant amount of heat during operation, requiring additional cooling mechanisms, such as fans or heat sinks. Transistors, on the other hand, generate less heat and may not need additional cooling in many applications.
  • Portability: Transistors are very portable due to their small size and low power consumption, which makes them suitable for portable electronic devices such as smartphones, laptops, and portable devices. Vacuum tubes, due to their size and power requirements, are not practical for portable applications.
  • Cost: Transistors are often cheaper to manufacture than vacuum tubes because they are smaller, require less material and can be mass-produced using modern semiconductor manufacturing processes. Vacuum tubes are relatively more expensive to produce and can be used in specialized applications where their unique characteristics are required.

In summary, although both transistors and vacuum valves are electronic devices used to amplify and switch signals, transistors offer advantages such as their smaller size, lower power consumption, higher reliability, faster switching speeds, and portability, making them the preferred choice in most modern electronic applications.

Vacuum tubes, on the other hand, are still used in certain specialized applications where their unique characteristics are beneficial, such as in high-power amplifiers, guitar amplifiers and some specialized audio applications. However, transistors have largely replaced vacuum valves in most conventional electronic applications due to their numerous advantages.


Assembly code, also known as assembly language code, has its origins in the early days of computer programming, when computers were still in their infancy. Assembly code was one of the first high-level programming languages developed to write software for early computer systems.

Early computers, such as ENIAC and UNIVAC, used machine code, which is a binary representation of instructions and data that the computer’s CPU can understand and execute directly. Machine code consists of sequences of binary digits (0 and 1) that represent instructions and data in a format that is not easily readable by humans.

As computers became more complex and the need for more effective programming methods arose, assembly language was developed as a step above machine code. Assembly language is a low-level programming language that uses mnemonic symbols or shortcodes to represent instructions and data that the computer’s CPU can understand and execute. These mnemonic symbols are more readable than binary digits, making it easier for programmers to write and understand code.

The first assembler, called “assembly program”, was developed in the early 50s for the UNIVAC I computer by Grace Hopper and her team. This early form of assembly language used mnemonic symbols to represent instructions and data in machine code. Over time, assembly languages were developed for other computer systems, each with its own syntax and instruction set specific to the computer’s target architecture.

Assembly code allowed programmers to write software at a higher level of abstraction than machine code, making it easier and faster to develop complex programs for early computers. It also paved the way for the development of high-level programming languages, such as FORTRAN, COBOL, and C, which provided even higher levels of abstraction and improved software development productivity.

Today, assembly language is still used in certain specialized areas, such as embedded systems programming, device driver development, and reverse engineering. However, with the advent of more advanced high-level programming languages and modern software development tools, the use of assembly language has become less prevalent in mainstream software development compared to high-level languages.

IBM 7000

The IBM 7000 series was a family of mainframe computers manufactured by IBM in the 1950s and 1960s. IBM 7000 series computers were known for their high performance, reliability and advanced features for their time. They were used in various applications, such as scientific and engineering calculations, enterprise data processing, and military and government applications.

IBM 7000 series computers were introduced in the late 1950s and offered a wide range of models with varying levels of performance and capabilities. Some of the most prominent models of the IBM 7000 series were the IBM 7040, the IBM 7090 and the IBM 7094.

IBM 7000 series computers were based on vacuum tube technology, which was the dominant technology for electronic computers at the time. The vacuum tubes were large, consumed a lot of energy and generated a lot of heat, so they needed very powerful cooling systems. However, they offered reliable and fast computing power for their time.

IBM 7000 series computers used punch card input/output (I/O) devices for data storage and retrieval, and magnetic tape drives for large-scale data storage. They had advanced features, such as floating-point arithmetic for scientific calculations, multiple programming languages, and support for multiprogramming, which allowed multiple programs to run simultaneously on the same computer.

IBM 7000 series computers were widely used in various industries, such as scientific research, government agencies, and large enterprises, for a wide range of applications, such as scientific calculations, engineering simulations, financial modeling, and data processing. They were known for their reliability and performance, and played an important role in the advancement of computer technology during the early years of the computer age.

IBM 1620

The IBM 1620 was a scientific and engineering computer introduced by IBM in 1959. It was a compact and relatively affordable computer that was widely used in small and medium-sized enterprises, research institutions and educational centers. The IBM 1620 was considered a mid-range computer among mainframes and minicomputers, and was known for its versatility, reliability, and ease of use.

The IBM 1620 offered decimal arithmetic, making it suitable for scientific and engineering calculations that required high precision. It had a word length of 20 bits and a memory capacity of up to 60,000 decimal digits, relatively small compared to mainframe computers of the time, but sufficient for many applications. The computer used punched card input/output (I/O) devices for data storage and retrieval, and was compatible with a wide range of peripherals, such as printers, card readers, and card punches.

One of the most prominent features of the IBM 1620 was its autocoder programming system, which offered an assembler-like programming environment and made it easier for users to write software programs. The auto-coding system used symbolic mnemonics for instructions and supported high-level programming constructs, such as loops and conditional statements, making programming more accessible to non-experts.

The IBM 1620 was used in a variety of applications, including scientific calculations, engineering simulations, and enterprise data processing. It was widely used in educational institutions to teach computer programming and as a research tool in scientific and engineering fields. It was also used in business environments for tasks such as payroll processing, inventory management, and scientific data analysis.

The IBM 1620 was an important contribution to the early days of the computer industry, as it made computing more accessible to a greater number of users thanks to its relatively low cost and ease of use. It helped democratize computing and expand its reach beyond large companies and research institutions, paving the way for the development of smaller, more affordable computers in the future.


The PDP-1 (Programmed Data Processor-1) was a computer model manufactured by Digital Equipment Corporation (DEC) in the 1960s. It was one of the first and most influential minicomputers, and played an important role in the development of computer science, software engineering, and video games.

The PDP-1 was introduced by DEC in 1959 and noted for being one of the first commercially available computers to use transistors instead of vacuum tubes. It had a word length of 18 bits and a memory capacity of 4,096 words (or 72 kilobits), which was considered relatively large for its time. It also had a screen and a stylus for interactive computing, which made it a pioneering system in human-computer interaction.

The PDP-1 was widely used in research institutions, educational centers, and industrial laboratories for various applications, such as scientific calculations, real-time control systems, and graphical visualization applications. It was also popular with computer hobbyists and enthusiasts, who used it to experiment with programming and develop innovative software.

One of the notable features of the PDP-1 was its software environment, which included the first implementation of assembly language, called PAL (Program Assembler Language), which facilitated the writing of software programs for the PDP-1. The PDP-1 also supported various programming languages, such as FORTRAN, assembly language, and machine language.

The PDP-1 is especially famous for its role in early video game history.

The PDP-1 was a pioneering computer that had a significant impact on the early history of computing, software development, and video games. He laid the foundation for the development of minicomputers and influenced the design and architecture of later computer systems. His legacy can still be seen in modern computing and gaming technologies, and remains an important milestone in the evolution of computer technology.

See also, for additional details, our computer and computing blog: Third generation of computers, Integrated circuits, 1964-1971; Fifth generation of computers, 1980 onwards, features; What are the 5 generations of computers or computer technology?

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