The history of computing hardware starting at 1960 is marked by the conversion from vacuum tube to solid-state devices such as transistors and then integrated circuit (IC) chips. Around 1953 to 1959, discrete transistors started being considered sufficiently reliable and economical that they made further vacuum tube computers uncompetitive. Metal–oxide–semiconductor (MOS) large-scale integration (LSI) technology subsequently led to the development of semiconductor memory in the mid-to-late 1960s and then the microprocessor in the early 1970s. This led to primary computer memory moving away from magnetic-core memory devices to solid-state static and dynamic semiconductor memory, which greatly reduced the cost, size, and power consumption of computers. These advances led to the miniaturized personal computer (PC) in the 1970s, starting with home computers and desktop computers, followed by laptops and then mobile computers over the next several decades.
Second generation
For the purposes of this article, the term "second generation" refers to computers using discrete transistors, even when the vendors referred to them as "third-generation". By 1960 transistorized computers were replacing vacuum tube computers, offering lower cost, higher speeds, and reduced power consumption. The marketplace was dominated by IBM and the seven dwarfs:
IBM The BUNCH Burroughs UNIVAC NCR Control Data Corporation (CDC) Honeywell General Electric RCA. Some examples of 1960s second generation computers from those vendors are:
the IBM 1401, the IBM 7090/7094, and the IBM System/360; the Burroughs 5000 series; the UNIVAC 1107; the NCR 315; the CDC 1604 and the CDC 3000 series; the Honeywell 200, Honeywell 400, and Honeywell 800; the GE-400 series and the GE-600 series; the RCA 301, 3301, 501, and the Spectra 70 series. However, some smaller companies made significant contributions. Also, towards the end of the second generation Digital Equipment Corporation (DEC) was a serious contender in the small and medium machine marketplace. Meanwhile, second-generation computers were also being developed in the USSR as, e.g., the Razdan family of general-purpose digital computers created at the Yerevan Computer Research and Development Institute. The second-generation computer architectures initially varied; they included character-based decimal computers, sign-magnitude decimal computers with a 10-digit word, sign-magnitude binary computers, and ones' complement binary computers, although Philco, RCA, and Honeywell, for example, had some computers that were character-based binary computers and Digital Equipment Corporation (DEC) and Philco, for example, had two's complement computers. With the advent of the IBM System/360, two's complement became the norm for new product lines. The most common word sizes for binary mainframes were 36 and 48 bits, although entry-level and midrange machines used smaller words, e.g., 12 bits, 18 bits, 24 bits, 30 bits. All but the smallest machines had asynchronous I/O channels and interrupts. Typically binary computers with word size up to 36 bits had one instruction per word, binary computers with 48 bits per word had two instructions per word and the CDC 60-bit machines could have two, three, or four instructions per word, depending on the instruction mix; the Burroughs B5000, B6500/B7500 and B8500 lines are notable exceptions to this. First-generation computers with data channels (I/O channels) had a basic DMA interface to the channel cable. The second generation saw both simpler, e.g., channels on the CDC 6000 series had no DMA, and more sophisticated designs, e.g., the 7909 on the IBM 7090 had limited computational, conditional branching and interrupt system. By 1960, magnetic core was the dominant memory technology, although there were still some new machines using drums and delay lines during the 1960s. Magnetic thin film and rod memory were used on some second-generation machines, but advances in core technology meant they remained niche players until semiconductor memory displaced both core and thin film. In the first generation, word-oriented computers typically had a single accumulator and an extension, referred to as, e.g., Upper and Lower Accumulator, Accumulator and Multiplier-Quotient (MQ) register. In the second generation, it became common for computers to have multiple addressable accumulators. On some computers, e.g., PDP-6, the same registers served as accumulators and index registers, making them an early example of general-purpose registers. In the second generation there was considerable development of new address modes, including truncated addressing on, e.g., the Philco TRANSAC S-2000, the UNIVAC III, and automatic index register incrementing on, e.g., the RCA 601, UNIVAC 1107, and the GE-600 series. Although index registers were introduced in the first generation under the name B-line, their use became much more common in the second generation. Similarly, indirect addressing became more common in the second generation, either in conjunction with index registers or instead of them. While first-generation computers typically had a small number of index registers or none, several lines of second-generation computers had large numbers of index registers, e.g., Atlas, Bendix G-20, IBM 7070. The first generation had pioneered the use of special facilities for calling subroutines, e.g., TSX on the IBM 709. In the second generation, such facilities were ubiquitous; some examples are:
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