IBM PC keyboard
The IBM PC keyboard is the original input device designed for the IBM Personal Computer (model 5150), released on August 12, 1981, featuring an 83-key QWERTY layout with capacitive buckling spring switches, a dedicated Intel 8048 microcontroller for generating scan codes, and a 5-pin DIN connector via a 6-foot coiled cable.[1][2][3] It measures approximately 19.5 inches wide by 7.8 inches deep by 2.3 inches high, weighs 6.2 pounds, and supports adjustable tilt angles of 5° or 15° for ergonomic use, along with tactile and audible feedback on keypresses.[2][3] This keyboard, part of the Model F series, established foundational standards for personal computer input devices through its durable all-metal construction, support for N-key rollover, a 16-character type-ahead buffer to handle rapid typing, and LED indicators for Caps Lock, Num Lock, and Scroll Lock states.[2][3] The layout includes a central typewriter section, ten programmable function keys (F1–F10) on the left side, and a 15-key numeric and cursor keypad on the right, enabling compatibility with MS-DOS and early applications while supporting 256 characters through standard and extended ASCII encoding.[2][3] Special functions, such as system reset via Ctrl+Alt+Del and Print Screen via Shift+PrtSc, were integrated directly into the hardware, influencing command conventions in computing.[2] The IBM PC keyboard's design emphasized reliability and user comfort, powering the rapid adoption of the IBM PC platform and serving as a precursor to subsequent models like the 84-key version for the IBM PC AT in 1984 and the more cost-effective Model M buckling spring keyboards introduced in 1985.[1][3] Available in multiple language variants including U.S. English, French, German, Italian, Spanish, and U.K. English, it connected serially to the system board via interrupt IRQ1 and ports 60h/61h, setting interoperability norms for PC-compatible hardware that persist in modern systems.[3][2] Its introduction marked a pivotal shift toward standardized, high-quality peripherals in personal computing, contributing to IBM's dominance in the early 1980s market.[1]History and Development
Origins and Design Process
In the early 1980s, IBM's development team for the Personal Computer (model 5150) decided to incorporate a standalone keyboard to enhance usability, allowing it to be positioned independently from the system unit via a 6-foot coiled cable connected through a serial interface, which facilitated flexible desk arrangements in office settings.[4] This design choice stemmed from the project's skunkworks approach under Don Estridge's leadership in Boca Raton, Florida, aiming to create an affordable business machine priced around $1,500 while prioritizing practical ergonomics for non-technical users.[1] The keyboard's layout and mechanics drew influences from prior technologies, including the QWERTY arrangement originating from 19th-century mechanical typewriters like the Remington No. 2, which optimized key sequencing to prevent jamming and became the standard for text input.[5] Additional inspirations came from the Teletype ASR-33, an electromechanical terminal popular in the 1960s and 1970s for its reliable alphanumeric input over communication lines, and IBM's own 3270 terminal keyboards, which emphasized durable, typewriter-style layouts for data entry in enterprise environments.[5] The core design was directly adapted from the IBM System/23 Datamaster's 83-key keyboard, with modifications to key legends for general-purpose computing, such as replacing specialized labels like "HELP" with function keys like F4.[6] Engineers, including members of the Boca Raton team such as David J. Bradley, focused on reliability and tactile feedback, selecting buckling spring mechanisms mounted over a capacitive printed circuit board for non-contact switch actuation, ensuring longevity in demanding office use with over 100 million cycles per key.[4] The initial specification featured 83 keys with fixed typematic repeat rates and primarily unidirectional scan code transmission, emphasizing construction durability to withstand repeated professional handling.[6] This buckling spring technology, providing crisp auditory and haptic response through catastrophic column buckling, was protected by U.S. Patent 4,118,611, filed in 1977 and issued to IBM inventor Richard Hunter Harris in 1978.[7]Introduction with IBM PC
The IBM Personal Computer Model 5150, commonly known as the IBM PC, was announced on August 12, 1981, at a press event in New York City's Waldorf-Astoria Hotel, marking IBM's entry into the personal computing market. Developed by a team in Boca Raton, Florida, the system featured the keyboard as a detachable peripheral connected via a coiled cable, included in the base configuration priced at $1,565 for the unit with 16 KB RAM and no disk drives.[1][8] The original IBM PC keyboard, known as the Model F, comprised 83 keys arranged in a layout with a 10-key numeric keypad and separate dedicated cursor keys in an inverted-T configuration, designed for compatibility with the system's monochrome display adapter (MDA) and text-based interfaces. It integrated seamlessly with the Intel 8088 processor running at 4.77 MHz and the included IBM BASIC interpreter, serving as the primary input device for booting into PC-DOS 1.0 and performing command-line operations in a era dominated by keyboard-driven navigation.[9] Manufactured in the United States using buckling spring key switches, the keyboard was engineered for durability, with each switch rated for up to 100 million keypresses, reflecting IBM's emphasis on reliability for business and professional use. At launch, the system lacked built-in mouse support, making the keyboard essential for all user interaction, including cursor movement and menu selection in early software applications. Its design influences from typewriter keyboards contributed to a familiar typing experience for office workers transitioning to computing.[10][11]Evolution to Standards
In 1984, IBM introduced the PC/AT model, which featured an enhanced 84-key keyboard layout based on the earlier Model F design, incorporating a new SysRq (System Request) key to support multitasking capabilities on the 80286 processor. This addition addressed the need for switching between operating systems or sessions, marking a step toward greater functionality in personal computing peripherals. The layout separated the numeric keypad more distinctly from the main typing area and included three status LED indicators for Caps Lock, Num Lock, and Scroll Lock, improving user feedback.[6] By 1986, IBM released the Model M keyboard, establishing it as a durable industry benchmark with its patented buckling spring mechanism—retaining the tactile feedback of the original design but housed in a more robust, injection-molded plastic casing for enhanced longevity and reduced manufacturing costs. This model transitioned to the 101-key enhanced layout, repositioning function keys (F1–F12) to the top row, adding dedicated arrow keys, and including dual Ctrl and Alt keys, which became foundational for PC compatibility. The Model M's reliability, with a projected lifespan exceeding 25 million keystrokes per key, influenced widespread adoption among enterprise users.[12][6][13] The IBM PC keyboard layouts gained standardization through influences from ANSI and ISO guidelines, with the 101/102-key configuration formalized as a de facto industry standard by the late 1980s, as PC clones from manufacturers like Compaq and Dell adopted compatible designs to ensure interoperability with IBM's BIOS and software ecosystem. Compaq's early 1982 Portable PC and subsequent Deskpro models mirrored the core key arrangements, accelerating market fragmentation while promoting uniformity. In the 1990s, the layout evolved further to the 104/105-key variant, incorporating Windows and Menu keys to align with Microsoft Windows 95's interface requirements, yet preserving backward compatibility with legacy PC applications through retained scan codes and key positions.[6][12] By the 2000s, IBM's proprietary keyboard production declined as the company shifted focus from hardware manufacturing, culminating in the 2005 sale of its PC division to Lenovo, which favored third-party suppliers adhering to open USB and PS/2 standards. This transition rendered IBM-specific designs obsolete in mainstream markets, with clones and OEMs like Dell standardizing on cost-effective membrane keyboards compliant with USB HID protocols, effectively commoditizing the PC input device. Following IBM's exit from the market, Unicomp, Inc. acquired the rights and tooling, continuing to manufacture new Model M keyboards using the buckling spring mechanism as of 2025.[14][12][15]Physical Layout and Design
Key Arrangement
The standard IBM PC keyboard layout for the original 83-key Model F organizes keys into distinct blocks for efficient data entry and navigation, establishing a design that became influential in personal computing. The central alphanumeric section follows the QWERTY arrangement derived from typewriter standards, comprising approximately 47 keys in the typewriter block, including the number/symbol row (14 keys from tilde/backtick to Backspace), the Q-row (11 keys from Tab to P), the A-row (12 keys from Caps Lock to Enter), and the Z-row (11 keys from left Shift to right Shift, including spacebar).[16] This structure prioritizes touch-typing efficiency, with home row keys (ASDF for left hand, JKL; for right) positioned for natural finger placement.[6] To the left of the alphanumeric block is a dedicated 2x5 block of 10 programmable function keys (F1–F10), arranged in two vertical columns for access during software interactions, often used for menu navigation or commands in early PC applications.[17] To the right lies a 15-key numeric keypad, mimicking a calculator layout for rapid numerical input in business and spreadsheet applications. It includes a Num Lock toggle key at the top left, followed by rows for division (/), multiplication (*), subtraction (-); the numbers 7-9, 4-6, 1-3; and a bottom row spanning 0 (double-width), decimal point (.), and Enter (tall key), with addition (+) positioned at the bottom right of the upper section.[11] When Num Lock is active, these keys input digits and operators; otherwise, they serve navigation functions such as Home (7), up arrow (8), Page Up (9), left arrow (4), right arrow (6), End (1), down arrow (2), Page Down (3), Insert (0), and Delete (.), providing integrated cursor control without a separate cluster.[6] Modifier keys are placed for chorded inputs: left Ctrl at the bottom left (below the Z-row), two Shift keys flanking the bottom row (left below Z, right below Enter), and Caps Lock above the left Shift in the standard typewriter position, with Tab above Caps Lock on the left.[6] The keyboard lacks Alt keys, which were introduced in later models.[17]Physical Features
The IBM PC keyboard, specifically the original 83-key Model F introduced with the IBM 5150 Personal Computer in 1981, features a robust buckling spring switch mechanism that provides distinctive tactile and audible feedback. Each key employs a capacitive buckling spring design, where a coiled spring buckles under pressure to alter the capacitance detected by underlying sensors, enabling precise key registration without physical contact between moving parts. This mechanism contributes to the keyboard's renowned durability, rated for up to 100 million keystroke cycles per switch.[18][11] The keyboard's casing consists of a low-profile plastic enclosure reinforced with a steel mounting plate, giving it an overall thickness of approximately 2.25 inches (57 mm) and a sturdy build that enhances stability during use. Weighing about 6 pounds (2.7 kg), the design prevents sliding on desks, supported further by non-slip feet. Adjustable tilt legs allow for ergonomic positioning at 5° or 15° angles, promoting user comfort without additional accessories.[11][19] Keycaps are constructed from high-quality polybutylene terephthalate (PBT) plastic with dye-sublimated legends, ensuring fade-resistant printing that withstands prolonged use. These keycaps maintain a uniform height of approximately 0.75 inches (19 mm) across all keys, facilitating consistent typing experience. The keyboard connects via a permanently attached, coiled 5-pin DIN cable measuring about 6 feet (1.83 m) in length, shielded for reliable signal transmission; later variants, such as the Model M, introduced detachable cables for improved modularity.[10][18][11]Size and Ergonomics
The IBM PC keyboard, specifically the original 83-key Model F variant introduced with the IBM 5150 in 1981, features compact dimensions suited to desktop environments of the era: approximately 19.5 inches (496 mm) in width, 7.8 inches (198 mm) in depth, and 2.3 inches (58 mm) in height, excluding tilt adjustments.[16] These measurements reflect its low-profile enclosure design, which prioritized durability and integration with the PC system unit over portability. Weighing around 6.2 pounds (2.8 kg), the keyboard was inherently desk-bound, lacking features for mobile use and incompatible with emerging laptop form factors at the time.[16] Ergonomically, the keyboard employs a fixed base height with no integrated wrist rest, relying instead on adjustable riser feet that allow tilting at 5° or 15° angles to alleviate wrist strain during extended typing.[16] This mechanism was intended to support prolonged office workflows, with key spacing set at 0.75 inches (19 mm) center-to-center to accommodate standard touch-typing techniques. The buckling spring key mechanism provides tactile feedback that some users found comfortable for long sessions, though the overall straight-row layout demanded neutral wrist positioning without angular accommodation. Critiques of early computer keyboards emerged in the 1980s as repetitive strain injury (RSI) rates rose among operators, with general workstation designs, including fixed keyboard positions, implicated in promoting repetitive motions that contributed to musculoskeletal disorders.Key Functions and Meanings
Keys from Typewriters
The IBM PC keyboard retained the QWERTY layout originally developed in the 1870s by Christopher Latham Sholes for the Remington No. 2 typewriter, arranging keys to separate commonly used letter pairs and minimize mechanical jamming of typebars.[20][21] This design directly influenced the alphanumeric section of the IBM Model F keyboard introduced with the 1981 IBM PC, preserving the familiar typewriter arrangement for typists transitioning to computers.[22] The home row—A-S-D-F for the left hand and J-K-L for the right—served as the foundational reference for touch typing, positioning the most frequent letters under the strongest fingers to promote efficiency, a convention established during the typewriter era and adopted unchanged in the IBM PC layout.[23] The Enter key on the IBM PC keyboard, designed as a large L-shaped key spanning two positions in the top-right row, originated from the carriage return mechanism on mechanical typewriters, where it advanced the paper to a new line and reset the typing position.[24] This form factor evolved in electric typewriters of the 1940s and 1950s, replacing levers with dedicated keys for line advancement, and was incorporated into the IBM PC to maintain compatibility with typewriter-based workflows.[25] Shift keys, positioned on both sides of the keyboard, enabled access to uppercase letters and symbols by mechanically elevating the typebars on typewriters, a dual-shift system carried over directly to the IBM PC without alteration in placement or function.[26] The Caps Lock key, located above the left Shift, locked the shift mechanism for continuous uppercase typing—a feature from early 20th-century typewriters that latched the shift in place until released—and retained its position on the IBM PC keyboard to support legacy typing habits.[27] The Tab key, situated above the left Caps Lock, provided fixed indentation for paragraphs and tables by engaging mechanical tabulator stops on typewriters, advancing the carriage a set distance; this indentation role and left-side placement were preserved in the IBM PC design.[28][29] The spacebar, spanning the full width of the keyboard bottom row, inserted uniform gaps between words as on typewriters, where it mechanically advanced the carriage by one character space, and this wide, central positioning was adopted in the IBM PC to replicate the tactile feedback and efficiency of typewriter spacing.[22] The Backspace key, located at the top-right above the Enter key, allowed correction by moving the carriage leftward on typewriters, erasing or overstriking errors; early manual models used it for repositioning, and the IBM PC keyboard integrated it in a similar oversized format to facilitate precise deletions in text entry.[30] Punctuation keys such as the period, comma, and semicolon occupied fixed positions in the QWERTY layout—period and comma on the right home row under the right pinky and ring fingers, semicolon beside the L key—to optimize typing flow by placing high-frequency symbols near the home row for quick access without disrupting rhythm, a standardization from typewriter designs that the IBM PC keyboard inherited to enhance typist productivity.[20][31]Keys from Teletype
The control keys on the IBM PC keyboard, such as Ctrl, Esc, Break, and Print Screen, trace their origins to teletype machines, particularly the influential Teletype Model 33 ASR introduced in 1963, which implemented the 7-bit ASCII standard as a successor to earlier 5-bit Baudot code systems and shaped early computer input conventions.[32][33] These keys were adapted for command and signaling functions in computing, reflecting the transition from electromechanical teleprinters to digital terminals. The Ctrl key, featured on the ASR-33 keyboard, originated as a modifier to produce ASCII control characters, such as Ctrl+C to interrupt transmission or Ctrl+S and Ctrl+Q for software flow control in serial communications.[34] On the IBM PC's 83-key layout, it was positioned at the bottom left to facilitate multi-key combinations like Ctrl+Alt+Del for rebooting or task management in DOS.[35] The Esc key, also present on the Model 33, generated the ASCII escape character (code 27) for initiating control sequences or mode shifts, often produced by pressing the dedicated Esc key or a combination like Ctrl+Shift+K.[36] In the IBM PC design, it was placed at the top left corner for rapid access to cancel or abort operations in applications.[37] The Break function derived from teletype practices of sending line break signals to interrupt or halt transmission by briefly opening the current loop circuit, a technique rooted in 19th-century telegraphy.[38] On the original IBM PC keyboard, it was activated via Ctrl + the Scroll Lock key to pause or terminate running processes in DOS, such as stopping batch files; the Scroll Lock key itself was later repurposed and combined with Pause as Pause/Break on enhanced layouts while retaining the interrupt capability via Ctrl + Break.[39] The Print Screen function evolved from teletype print commands that directed output to a printer, adapting the teleprinter's core function of rendering text for hard copy.[40] On the original IBM PC keyboard, it was activated by Shift + the keypad asterisk (*) key to capture the current text-mode screen contents and send them to the attached printer, with later variants introducing a dedicated Print Screen key where Shift + Print Screen could limit output to the active window.[35][41]Keys Specific to Computers
The IBM PC keyboard introduced several keys tailored for interaction with graphical and video displays, moving beyond the limitations of typewriter and teletype designs to support cursor-based navigation, text editing, and programmable shortcuts in early personal computing applications. These keys were part of the original 83-key layout, utilizing capacitive switches and an Intel 8048 microcontroller to generate scan codes for software interpretation, enabling efficient operation in text-mode environments like the IBM PC's monochrome display adapter.[16] Dedicated arrow keys for up, down, left, and right cursor movement marked a significant innovation, positioned in an inverted-T arrangement to the right of the main alphanumeric section and separate from the numeric keypad. Unlike earlier terminals, where cursor control often relied on overprinted symbols or multi-key combinations on a shared numeric pad, these standalone keys allowed precise, single-keystroke navigation in applications such as text editors and spreadsheets, with scan codes like 47H (up), 4BH (left), 50H (down), and 4DH (right). Their design facilitated smooth cursor positioning on the 25x80 character screen, enhancing usability for video display interactions.[16][17] The Insert and Delete keys provided essential editing capabilities for buffer-based text manipulation, with Insert toggling between insertion and overtype modes to shift characters rightward and Delete removing the character at or after the cursor. Positioned adjacent to the arrow keys, these supported early word processors like WordStar by enabling in-place modifications without rewriting entire lines, using scan codes 52H for Insert and 53H for Delete; Delete also formed part of the Ctrl+Alt+Del reset sequence for system recovery. This functionality addressed the needs of document creation on visual displays, where real-time editing replaced sequential tape or print-based workflows.[16][17][42] Navigation keys including Home, End, Page Up, and Page Down further optimized movement through documents and data sets, with Home jumping the cursor to the line start, End to the line end, Page Up scrolling upward by one screen (typically 25 lines), and Page Down scrolling downward similarly. Grouped in the keypad cluster with scan codes 47H (Home), 4FH (End), 49H (Page Up), and 51H (Page Down), these keys were vital for spreadsheets and multi-page text files, allowing rapid jumps and scrolls that Ctrl combinations could extend, such as Ctrl+Home to clear the screen. Their inclusion reflected the shift to windowed, scrollable interfaces on the PC, distinct from linear terminal scrolling.[16][17] Function keys F1 through F10, arranged in two vertical columns on the keyboard's left side, offered programmable flexibility for application-specific commands, generating scan codes from 3BH (F1) to 44H (F10) and extensible via Shift (F11-F20), Ctrl (F21-F30), or Alt (F31-F40) for up to 40 unique functions. Software could redefine them for shortcuts, such as F1 invoking help menus in early applications, promoting customizable workflows in programming and productivity tools. This block of 10 keys expanded on terminal precedents, providing a dedicated space for video display commands without conflicting with alphanumeric input.[16][17][42] The Num Lock key, located above the numeric keypad with scan code 45H, toggled the 15-key right-side pad between numeric entry and navigation modes, locking it for numbers while disabling cursor functions or vice versa, with Shift+Num Lock reversing the state. This dual-purpose design conserved space on the compact keyboard, supporting multitasking between data input and editing on the PC's display, a feature unique to its versatile architecture compared to fixed-function terminals.[16][17][42]Connection Interfaces
Original PC Connection
The original IBM PC keyboard, introduced with the IBM 5150 model in 1981, utilized a proprietary 5-pin DIN connector for direct attachment to the motherboard, facilitating a serial communication link between the keyboard and the host system. This round plug design carried essential signals including power, ground, a clock line generated by the keyboard, and a bidirectional data line for transmitting scan codes, enabling the keyboard's Intel 8048 microcontroller to interface with the system's 8255 programmable peripheral interface chip via I/O port 60h.[16] The pinout of the 5-pin DIN connector was configured as follows, with the keyboard mounted at a right angle on the system board and extending through the rear panel for external access:| Pin | Signal | Description |
|---|---|---|
| 1 | +Keyboard Clock | Clock signal from keyboard |
| 2 | +Keyboard Data | Bidirectional data line |
| 3 | -Keyboard Reset | Unused by keyboard |
| 4 | Ground | Common ground reference |
| 5 | +5 V | Power supply from host |