Second generation: transistors

In the second half of the 1950s bipolar junction transistors (BJTs) replaced vacuum tubes. Their use gave rise to the "second generation" computers. Initially, it was believed that very few computers would ever be produced or used. This was due in part to their size, cost, and the skill required to operate or interpret their results. Transistors greatly reduced computers' size, initial cost and operating cost. The bipolar junction transistor was invented in 1947.electrical current flows through the base-emitter path of a bipolar transistor, the transistor's collector-emitter path blocks electrical current (and the transistor is said to "turn full off"). If sufficient current flows through the base-emitter path of a transistor, that transistor's collector-emitter path also passes current (and the transistor is said to "turn full on"). Current flow or current blockage represent binary 1 (true) or 0 (false), respectively.Compared to vacuum tubes, transistors have many advantages: they are less expensive to manufacture and are much faster, switching from the condition 1 to 0 in millionths or billionths of a second. Transistor volume is measured in cubic millimeters compared to vacuum tubes' cubic centimeters. Transistors' lower operating temperature increased their reliability, compared to vacuum tubes. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. If no

Typically, second-generation computers were composed of large numbers of printed circuit boards such as the IBM Standard Modular System each carrying one to four logic gates or flip-flops. A second generation computer, the IBM 1401, captured about one third of the world market. IBM installed more than one hundred thousand 1401s between 1960 and 1964— This period saw the only Italian attempt: the ELEA by Olivetti, produced in 110 units.

This RAMAC DASD is being restored at the Computer History Museum.

Transistorized electronics improved not only the CPU (Central Processing Unit), but also the peripheral devices. The IBM 350 RAMAC was introduced in 1956 and was the world's first disk drive. The second generation disk data storage units were able to store tens of millions of letters and digits. Multiple Peripherals can be connected to the CPU, increasing the total memory capacity to hundreds of millions of characters. Next to the fixed disk storage units, connected to the CPU via high-speed data transmission, were removable disk data storage units. A removable disk stack can be easily exchanged with another stack in a few seconds. Even if the removable disks' capacity is smaller than fixed disks,' their interchangeability guarantees a nearly unlimited quantity of data close at hand. But magnetic tape provided archival capability for this data, at a lower cost than disk.

Many second generation CPUs delegated peripheral device communications to a secondary processor. For example, while the communication processor controlled card reading and punching, the main CPU executed calculations and binary branch instructions. One databusfetch-execute cycle rate, and other databusses would typically serve the peripheral devices. On the PDP-1, the core memory's cycle time was 5 microseconds; consequently most arithmetic instructions took 10 microseconds (100,000 operations per second) because most operations took at least two memory cycles; one for the instruction, one for the operand data fetch. would bear data between the main CPU and core memory at the CPU's

During the second generation remote terminal units (often in the form of teletype machines like a Friden Flexowriter) saw greatly increased use. Telephone connections provided sufficient speed for early remote terminals and allowed hundreds of kilometers separation between remote-terminals and the computing center. Eventually these stand-alone computer networks would be generalized into an interconnected network of networks — the Internet.

Second generation: transistors

In the second half of the 1950s bipolar junction transistors (BJTs) replaced vacuum tubes. Their use gave rise to the "second generation" computers. Initially, it was believed that very few computers would ever be produced or used. This was due in part to their size, cost, and the skill required to operate or interpret their results. Transistors greatly reduced computers' size, initial cost and operating cost. The bipolar junction transistor was invented in 1947.electrical current flows through the base-emitter path of a bipolar transistor, the transistor's collector-emitter path blocks electrical current (and the transistor is said to "turn full off"). If sufficient current flows through the base-emitter path of a transistor, that transistor's collector-emitter path also passes current (and the transistor is said to "turn full on"). Current flow or current blockage represent binary 1 (true) or 0 (false), respectively.Compared to vacuum tubes, transistors have many advantages: they are less expensive to manufacture and are much faster, switching from the condition 1 to 0 in millionths or billionths of a second. Transistor volume is measured in cubic millimeters compared to vacuum tubes' cubic centimeters. Transistors' lower operating temperature increased their reliability, compared to vacuum tubes. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. If no

Typically, second-generation computers were composed of large numbers of printed circuit boards such as the IBM Standard Modular System each carrying one to four logic gates or flip-flops. A second generation computer, the IBM 1401, captured about one third of the world market. IBM installed more than one hundred thousand 1401s between 1960 and 1964— This period saw the only Italian attempt: the ELEA by Olivetti, produced in 110 units.

This RAMAC DASD is being restored at the Computer History Museum.

Transistorized electronics improved not only the CPU (Central Processing Unit), but also the peripheral devices. The IBM 350 RAMAC was introduced in 1956 and was the world's first disk drive. The second generation disk data storage units were able to store tens of millions of letters and digits. Multiple Peripherals can be connected to the CPU, increasing the total memory capacity to hundreds of millions of characters. Next to the fixed disk storage units, connected to the CPU via high-speed data transmission, were removable disk data storage units. A removable disk stack can be easily exchanged with another stack in a few seconds. Even if the removable disks' capacity is smaller than fixed disks,' their interchangeability guarantees a nearly unlimited quantity of data close at hand. But magnetic tape provided archival capability for this data, at a lower cost than disk.

Many second generation CPUs delegated peripheral device communications to a secondary processor. For example, while the communication processor controlled card reading and punching, the main CPU executed calculations and binary branch instructions. One databusfetch-execute cycle rate, and other databusses would typically serve the peripheral devices. On the PDP-1, the core memory's cycle time was 5 microseconds; consequently most arithmetic instructions took 10 microseconds (100,000 operations per second) because most operations took at least two memory cycles; one for the instruction, one for the operand data fetch. would bear data between the main CPU and core memory at the CPU's

During the second generation remote terminal units (often in the form of teletype machines like a Friden Flexowriter) saw greatly increased use. Telephone connections provided sufficient speed for early remote terminals and allowed hundreds of kilometers separation between remote-terminals and the computing center. Eventually these stand-alone computer networks would be generalized into an interconnected network of networks — the Internet.

Post-1960: third generation and beyond

The explosion in the use of computers began with 'Third Generation' computers. These relied on Jack St. Clair Kilby's^[90] and Robert Noyce's^[91] independent invention of the integrated circuit (or microchip), which later led to the invention of the microprocessor,^[92] by Ted Hoff, Federico Faggin, and Stanley Mazor at Intel.^[93] The integrated circuit in the image on the right, for example, an Intelmicrocontroller that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of EPROM, and I/O in the same chip. 8742, is an 8-bit

During the 1960s there was considerable overlap between second and third generation technologies.^[94] IBM implemented its IBM Solid Logic Technologyhybrid circuits for the IBM System/360 in 1964. As late as 1975, Sperry Univac continued the manufacture of second-generation machines such as the UNIVAC 494. The Burroughs large systems such as the B5000 were stack machinespushdown automatons were also implemented in minicomputers and microprocessors later, which influenced programming language design. Minicomputers served as low-cost computer centers for industry, business and universities.^[95] It became possible to simulate analog circuits with the simulation program with integrated circuit emphasis, or SPICE (1971) on minicomputers, one of the programs for electronic design automation (EDA). The microprocessor led to the development of the microcomputer, small, low-cost computers that could be owned by individuals and small businesses. Microcomputers, the first of which appeared in the 1970s, became ubiquitous in the 1980s and beyond. Steve Wozniak, co-founder of Apple Computer, is credited with developing the first mass-market home computers. However, his first computer, the Apple I, came out some time after the MOS Technology KIM-1 and Altair 8800, and the first Apple computer with graphic and sound capabilities came out well after the Commodore PET. Computing has evolved with microcomputer architectures, with features added from their larger brethren, now dominant in most market segments. modules in which allowed for simpler programming. These

Systems as complicated as computers require very high reliability. ENIACHot-pluggable hard disks, like the hot-pluggable vacuum tubes of yesteryear, continue the tradition of repair during continuous operation. Semiconductor memories routinely have no errors when they operate, although operating systems like Unix have employed memory tests on start-up to detect failing hardware. Today, the requirement of reliable performance is made even more stringent when server farms are the delivery platform. Google has managed this by using fault-tolerant software to recover from hardware failures, and is even working on the concept of replacing entire server farms on-the-fly, during a service event.^[96] remained on, in continuous operation from 1947 to 1955, for eight years before being shut down. Although a vacuum tube might fail, it would be replaced without bringing down the system. By the simple strategy of never shutting down ENIAC, the failures were dramatically reduced.

In the twenty-first century, multi-core CPUs became commercially available. Content-addressable memory (CAM)^[97] has become inexpensive enough to be used in networking, although no computer system has yet implemented hardware CAMs for use in programming languages. Currently, CAMs (or associative arrays) in software are programming-language-specific. Semiconductor memory cell arrays are very regular structures, and manufacturers prove their processes on them; this allows price reductions on memory products. After semiconductor memories became commodities, computer software became less labor-intensive; programming codes became less arcane, more understandable.^[98] When the CMOS field effect transistor-based logic gates supplanted bipolar transistors, computer power consumption could decrease dramatically (A CMOS Field-effect transistor draws current during the 'transition' between logic states, unlike the higher current draw of a BJT). This has allowed computing to become a commodity which is now ubiquitous, embedded in many forms, from greeting cards and telephones to satellites. Computing hardware and its software have even become a metaphor for the operation of the universe.^[99]

An indication of the rapidity of development of this field can be inferred by the history of the seminal article.^[100] By the time that anyone had time to write anything down, it was obsolete. After 1945, others read John von Neumann's First Draft of a Report on the EDVAC, and immediately started implementing their own systems. To this day, the pace of development has continued, worldwide.

II. INPUT HARDWARE

Input hardware consists of external devices—that is, components outside of the computer’s CPU—that provide information and instructions to the computer. A light pen is a stylus with a light-sensitive tip that is used to draw directly on a computer’s video screen or to select information on the screen by pressing a clip in the light pen or by pressing the light pen against the surface of the screen. The pen contains light sensors that identify which portion of the screen it is passed over.

A mouse is a pointing device designed to be gripped by one hand. It has a detection device (usually a ball, a light-emitting diode [LED], or a low-powered laser) on the bottom that enables the user to control the motion of an on-screen pointer, or cursor, by moving the mouse on a flat surface. As the device moves across the surface, the cursor moves across the screen. To select items or choose commands on the screen, the user presses a button on the mouse. A joystick is a pointing device composed of a lever that moves in multiple directions to navigate a cursor or other graphical object on a computer screen.

A keyboard is a typewriter-like device that allows the user to type in text and commands to the computer. Some keyboards have special function keys or integrated pointing devices, such as a trackball or touch-sensitive regions that let the user’s finger motions move an on-screen cursor.

Touch-screen displays, which are video displays with a special touch-sensitive surface, are also becoming popular with personal electronic devices—examples include the Apple iPhone and Nintendo DS video game system. Touch-screen displays are also becoming common in everyday use. Examples include ticket kiosks in airports and automated teller machines (ATM).

An optical scanner uses light-sensing equipment to convert images such as a picture or text into electronic signals that can be manipulated by a computer. For example, a photograph can be scanned into a computer and then included in a text document created on that computer. The two most common scanner types are the flatbed scanner, which is similar to an office photocopier, and the handheld scanner, which is passed manually across the image to be processed.

A microphone is a device for converting sound into signals that can then be stored, manipulated, and played back by the computer. A voice recognition module is a device that converts spoken words into information that the computer can recognize and process.

A modem, which stands for modulator-demodulator, is a device that connects a computer to a telephone line or cable television network and allows information to be transmitted to or received from another computer. Each computer that sends or receives information must be connected to a modem. The digital signal sent from one computer is converted by the modem into an analog signal, which is then transmitted by telephone lines or television cables to the receiving modem, which converts the signal back into a digital signal that the receiving computer can understand.

A network interface card (NIC) allows the computer to access a local area network (LAN) through either a specialized cable similar to a telephone line or through a wireless (Wi-Fi) connection. The vast majority of LANs connect through the Ethernet standard, which was introduced in 1983.

III. OUTPUT HARDWARE

Output hardware consists of internal and external devices that transfer information from the computer’s CPU to the computer user. Graphics adapters, which are either an add-on card (called a video card) or connected directly to the computer’s motherboard, transmit information generated by the computer to an external display. Displays commonly take one of two forms: a video screen with a cathode-ray tube (CRT) or a video screen with a liquid crystal display (LCD). A CRT-based screen, or monitor, looks similar to a television set. Information from the CPU is displayed using a beam of electrons that scans a phosphorescent surface that emits light and creates images. An LCD-based screen displays visual information on a flatter and smaller screen than a CRT-based video monitor. Laptop computers use LCD screens for their displays.

Printers take text and image from a computer and print them on paper. Dot-matrix printers use tiny wires to impact upon an inked ribbon to form characters. Laser printers employ beams of light to draw images on a drum that then picks up fine black particles called toner. The toner is fused to a page to produce an image. Inkjet printers fire droplets of ink onto a page to form characters and pictures.

Computers can also output audio via a specialized chip on the motherboard or an add-on card called a sound card. Users can attach speakers or headphones to an output port to hear the audio produced by the computer. Many modern sound cards allow users to create music and record digital audio, as well.

IV. STORAGE HARDWARE

Storage hardware provides permanent storage of information and programs for retrieval by the computer. The two main types of storage devices are disk drives and memory. There are several types of disk drives: hard, floppy, magneto-optical, magnetic tape, and compact. Hard disk drives store information in magnetic particles embedded in a disk. Usually a permanent part of the computer, hard disk drives can store large amounts of information and retrieve that information very quickly. Floppy disk drives also store information in magnetic particles embedded in removable disks that may be floppy or rigid. Floppy disks store less information than a hard disk drive and retrieve the information at a much slower rate. While most computers still include a floppy disk drive, the technology has been gradually phased out in favor of newer technologies.

Magneto-optical disk drives store information on removable disks that are sensitive to both laser light and magnetic fields. They can store up to 9.1 gigabytes (GB) of data, but they have slightly slower retrieval speeds as opposed to hard drives. They are much more rugged than floppy disks, making them ideal for data backups. However, the introduction of newer media that is both less expensive and able to store more data has made magneto-optical drives obsolete.

Magnetic tape drives use magnetic tape similar to the tape used in VCR cassettes. Tape drives have a very slow read/write time, but have a very high capacity; in fact, their capacity is second only to hard disk drives. Tape drives are mainly used to back up data.

Compact disc drives store information on pits burned into the surface of a disc of reflective material (see CD-ROM). CD-ROMs can store up to 737 megabytes (MB) of data. A Compact Disc-Recordable (CD-R) or Compact Disc-ReWritable (CD-RW) drive can record data onto a specialized disc, but only the CD-RW standard allows users to change the data stored on the disc. A digital versatile disc (DVD) looks and works like a CD-ROM but can store up to 17.1 GB of data on a single disc. Like CD-ROMs, there are specialized versions of DVDs, such as DVD-Recordable (DVD-R) and DVD-ReWritable (DVD-RW), that can have data written onto them by the user. More recently Sony Electronics developed DVD technology called Blu-ray. It has much higher storage capacities than standard DVD media.

Memory refers to the computer chips that store information for quick retrieval by the CPU. Random access memory (RAM) is used to store the information and instructions that operate the computer's programs. Typically, programs are transferred from storage on a disk drive to RAM. RAM is also known as volatile memory because the information within the computer chips is lost when power to the computer is turned off. Read-only memory (ROM) contains critical information and software that must be permanently available for computer operation, such as the operating system that directs the computer's actions from start up to shut down. ROM is called nonvolatile memory because the memory chips do not lose their information when power to the computer is turned off.

A more recent development is solid-state RAM. Unlike standard RAM, solid state RAM can contain information even if there is no power supply. Flash drives are removable storage devices that utilize solid-state RAM to store information for long periods of time. Solid-state drives (SSD) have also been introduced as a potential replacement for hard disk drives. SSDs have faster access speeds than hard disks and have no moving parts. However, they are quite expensive and do not have the ability to store as much data as a hard disk. Solid-state RAM technology is also used in memory cards for digital media devices, such as digital cameras and media players.

Some devices serve more than one purpose. For example, floppy disks may also be used as input devices if they contain information to be used and processed by the computer user. In addition, they can be used as output devices if the user wants to store the results of computations on them.

V. HARDWARE CONNECTIONS

To function, hardware requires physical connections that allow components to communicate and interact. A bus provides a common interconnected system composed of a group of wires or circuitry that coordinates and moves information between the internal parts of a computer. A computer bus consists of two channels, one that the CPU uses to locate data, called the address bus, and another to send the data to that address, called the data bus. A bus is characterized by two features: how much information it can manipulate at one time, called the bus width, and how quickly it can transfer these data. In today’s computers, a series of buses work together to communicate between the various internal and external devices.