The system console, computer console, root console, operator's console, or console is the text entry and display device for system administration messages those from the BIOS or boot loader, the kernel, from the init system and from the system logger. It is a physical device consisting of a keyboard and a screen, traditionally is a text terminal, but may be a graphical terminal. System consoles are generalized to computer terminals, which are abstracted by virtual consoles and terminal emulators. Today communication with system consoles is done abstractly, via the standard streams, but there may be system-specific interfaces, for example those used by the system kernel. Prior to the development of alphanumeric CRT system consoles, some computers such as the IBM 1620 had console typewriters and front panels while the first programmable computer, the Manchester Baby, used a combination of electromechanical switches and a CRT to provide console functions—the CRT displaying memory contents in binary by mirroring the machine's Williams-Kilburn tube CRT-based RAM.
On traditional minicomputers, the console was a serial console, an RS-232 serial link to a terminal such as a DEC VT100. This terminal was kept in a secured room since it could be used for certain privileged functions such as halting the system or selecting which media to boot from. Large midrange systems, e.g. those from Sun Microsystems, Hewlett-Packard and IBM, still use serial consoles. In larger installations, the console ports are attached to multiplexers or network-connected multiport serial servers that let an operator connect a terminal to any of the attached servers. Today, serial consoles are used for accessing headless systems with a terminal emulator running on a laptop. Routers, enterprise network switches and other telecommunication equipment have RS-232 serial console ports. On PCs and workstations, the computer's attached keyboard and monitor have the equivalent function. Since the monitor cable carries video signals, it cannot be extended far. Installations with many servers therefore use keyboard/video multiplexers and video amplifiers to centralize console access.
In recent years, KVM/IP devices have become available that allow a remote computer to view the video output and send keyboard input via any TCP/IP network and therefore the Internet. Some PC BIOSes in servers support serial consoles, giving access to the BIOS through a serial port so that the simpler and cheaper serial console infrastructure can be used. Where BIOS support is lacking, some operating systems, e.g. FreeBSD and Linux, can be configured for serial console operation either during bootup, or after startup, it is possible to log in from the console. Depending on configuration, the operating system may treat a login session from the console as being more trustworthy than a login session from other sources. Command-line interface Console application Console server Linux console Virtual console Win32 console
On computer keyboards, the Esc key is a key used to generate the escape character. The escape character, when sent from the keyboard to a computer is interpreted by software as "stop", when sent from the computer to an external device marks the beginning of an escape sequence to specify operating modes or characteristics generally, it is now placed at the top left corner of the keyboard, a convention dating at least to the original IBM PC keyboard, though the key itself originated decades earlier with teletypewriters. The keyboard symbol for the ESC key is standardized in ISO/IEC 9995-7 as symbol 29, in ISO 7000 "Graphical symbols for use on equipment" as symbol ISO-7000-2029; this symbol is encoded in Unicode as U+238B broken circle with northwest arrow. The name of the equivalent key on some early Teletype Model 33 keyboards was labeled Alt Mode... the alternative mode of operation causing the escapement to treat the following one character in a special way. Much printers and computer terminals that would use escape sequences would take more than one following byte as part of a special sequence.
The VT05 CRT did not have an ESC key. As most computer users are no longer concerned with the details of controlling their computer's peripherals, the task for which the escape sequences were designed, the escape key was appropriated by application programmers, most to mean Stop; this use continues today in Microsoft Windows's use of escape as a shortcut in dialog boxes for No, Exit, Cancel, or Abort, as well as a common shortcut key for the Stop button in many web browsers. On machines running Microsoft Windows, prior to the implementation of the Windows key on keyboards, the typical practice for invoking the "start" button was to hold down the Control key and press escape; this key combination still works as of Windows 10. Microsoft Windows makes use of "Esc" for many key shortcuts. Many of these shortcuts have been present since Windows 3.0, through Windows XP, Windows Vista, Windows 7, Windows 8, Windows 10. In macOS, "Esc" closes or cancels a dialog box or sheet; the ⌘ Command+⌥ Option+⎋ Esc combination opens the Force Quit dialog box, allowing users to end non-responsive applications.
Another use for the Esc key, in combination with the Command key, is switching to Front Row, if installed. In most computer games, the escape key is used as a pause button and/or as a way to bring up the in-game menu containing ways to exit the program. In the vi family of text editors, escape is used to switch modes; this usage is due to escape being conveniently placed in what is now the tab position on the ADM-3A terminal keyboard used to develop vi, though it is now inconveniently placed. This is similar to how the extensive modifier keys in Emacs were used on the original keyboard, being placed together, but these keys have now been spread around the keyboard, becoming more difficult to use. Old keyboard Send/Receive printers, visual display units, would be controlled by escape sequences sent by the computer to the peripheral device, but there were situations where these devices could be used "off-line" with the keyboard connected to the output device, so the need could arise to type escape sequences "by hand" to control the peripheral.
Although such devices are long out of use, standard processing of ANSI Escape sequences similar to 1970's VT100, is implemented in both ANSI. SYS and other more modern pseudo-terminal interfaces used in Unix-like environments, one example being Linux consoles, meaning newer, higher-level abstractions haven't changed the fact that typing the escape key followed by something like the six characters [32.
MS-DOS is an operating system for x86-based personal computers developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, some operating systems attempting to be compatible with MS-DOS, are sometimes referred to as "DOS". MS-DOS was the main operating system for IBM PC compatible personal computers during the 1980s and the early 1990s, when it was superseded by operating systems offering a graphical user interface, in various generations of the graphical Microsoft Windows operating system. MS-DOS was the result of the language developed in the seventies, used by IBM for its mainframe operating system. Microsoft acquired the rights to meet IBM specifications. IBM re-released it on August 12, 1981 as PC DOS 1.0 for use in their PCs. Although MS-DOS and PC DOS were developed in parallel by Microsoft and IBM, the two products diverged after twelve years, in 1993, with recognizable differences in compatibility and capabilities. During its lifetime, several competing products were released for the x86 platform, MS-DOS went through eight versions, until development ceased in 2000.
MS-DOS was targeted at Intel 8086 processors running on computer hardware using floppy disks to store and access not only the operating system, but application software and user data as well. Progressive version releases delivered support for other mass storage media in greater sizes and formats, along with added feature support for newer processors and evolving computer architectures, it was the key product in Microsoft's growth from a programming language company to a diverse software development firm, providing the company with essential revenue and marketing resources. It was the underlying basic operating system on which early versions of Windows ran as a GUI, it is a flexible operating system, consumes negligible installation space. MS-DOS was a renamed form of 86-DOS – owned by Seattle Computer Products, written by Tim Paterson. Development of 86-DOS took only six weeks, as it was a clone of Digital Research's CP/M, ported to run on 8086 processors and with two notable differences compared to CP/M.
This first version was shipped in August 1980. Microsoft, which needed an operating system for the IBM Personal Computer hired Tim Paterson in May 1981 and bought 86-DOS 1.10 for $75,000 in July of the same year. Microsoft kept the version number, but renamed it MS-DOS, they licensed MS-DOS 1.10/1.14 to IBM, who, in August 1981, offered it as PC DOS 1.0 as one of three operating systems for the IBM 5150, or the IBM PC. Within a year Microsoft licensed MS-DOS to over 70 other companies, it was designed to be an OS. Each computer would have its own distinct hardware and its own version of MS-DOS, similar to the situation that existed for CP/M, with MS-DOS emulating the same solution as CP/M to adapt for different hardware platforms. To this end, MS-DOS was designed with a modular structure with internal device drivers, minimally for primary disk drives and the console, integrated with the kernel and loaded by the boot loader, installable device drivers for other devices loaded and integrated at boot time.
The OEM would use a development kit provided by Microsoft to build a version of MS-DOS with their basic I/O drivers and a standard Microsoft kernel, which they would supply on disk to end users along with the hardware. Thus, there were many different versions of "MS-DOS" for different hardware, there is a major distinction between an IBM-compatible machine and an MS-DOS machine; some machines, like the Tandy 2000, were MS-DOS compatible but not IBM-compatible, so they could run software written for MS-DOS without dependence on the peripheral hardware of the IBM PC architecture. This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, indeed the same design philosophy is embodied in Windows NT. However, in MS-DOS's early days, the greater speed attainable by programs through direct control of hardware was of particular importance for games, which pushed the limits of their contemporary hardware. Soon an IBM-compatible architecture became the goal, before long all 8086-family computers emulated IBM's hardware, only a single version of MS-DOS for a fixed hardware platform was needed for the market.
This version is the version of MS-DOS, discussed here, as the dozens of other OEM versions of "MS-DOS" were only relevant to the systems they were designed for, in any case were similar in function and capability to some standard version for the IBM PC—often the same-numbered version, but not always, since some OEMs used their own proprietary version numbering schemes —with a few notable exceptions. Microsoft omitted multi-user support from MS-DOS because Microsoft's Unix-based operating system, was multi-user; the company planned, over time, to improve MS-DOS so it would be indistinguishable from single-user Xenix, or XEDOS, which would run on the Motorola 68000, Zilog Z8000, the LSI-11. Microsoft advertised MS-DOS and Xenix together, listing the shared features of its "single-user OS" and "the multi-user, multi-tasking, UNIX-derived operating system", promising easy
Mainframe computers or mainframes are computers used by large organizations for critical applications. They are larger and have more processing power than some other classes of computers: minicomputers, servers and personal computers; the term referred to the large cabinets called "main frames" that housed the central processing unit and main memory of early computers. The term was used to distinguish high-end commercial machines from less powerful units. Most large-scale computer system architectures were established in the 1960s, but continue to evolve. Mainframe computers are used as servers. Modern mainframe design is characterized less by raw computational speed and more by: Redundant internal engineering resulting in high reliability and security Extensive input-output facilities with the ability to offload to separate engines Strict backward compatibility with older software High hardware and computational utilization rates through virtualization to support massive throughput. Hot-swapping of hardware, such as processors and memory.
Their high stability and reliability enable these machines to run uninterrupted for long periods of time, with mean time between failures measured in decades. Mainframes have high availability, one of the primary reasons for their longevity, since they are used in applications where downtime would be costly or catastrophic; the term reliability and serviceability is a defining characteristic of mainframe computers. Proper planning and implementation is required to realize these features. In addition, mainframes are more secure than other computer types: the NIST vulnerabilities database, US-CERT, rates traditional mainframes such as IBM Z, Unisys Dorado and Unisys Libra as among the most secure with vulnerabilities in the low single digits as compared with thousands for Windows, UNIX, Linux. Software upgrades require setting up the operating system or portions thereof, are non-disruptive only when using virtualizing facilities such as IBM z/OS and Parallel Sysplex, or Unisys XPCL, which support workload sharing so that one system can take over another's application while it is being refreshed.
In the late 1950s, mainframes had only a rudimentary interactive interface, used sets of punched cards, paper tape, or magnetic tape to transfer data and programs. They operated in batch mode to support back office functions such as payroll and customer billing, most of which were based on repeated tape-based sorting and merging operations followed by line printing to preprinted continuous stationery; when interactive user terminals were introduced, they were used exclusively for applications rather than program development. Typewriter and Teletype devices were common control consoles for system operators through the early 1970s, although supplanted by keyboard/display devices. By the early 1970s, many mainframes acquired interactive user terminals operating as timesharing computers, supporting hundreds of users along with batch processing. Users gained access through keyboard/typewriter terminals and specialized text terminal CRT displays with integral keyboards, or from personal computers equipped with terminal emulation software.
By the 1980s, many mainframes supported graphic display terminals, terminal emulation, but not graphical user interfaces. This form of end-user computing became obsolete in the 1990s due to the advent of personal computers provided with GUIs. After 2000, modern mainframes or phased out classic "green screen" and color display terminal access for end-users in favour of Web-style user interfaces; the infrastructure requirements were drastically reduced during the mid-1990s, when CMOS mainframe designs replaced the older bipolar technology. IBM claimed that its newer mainframes reduced data center energy costs for power and cooling, reduced physical space requirements compared to server farms. Modern mainframes can run multiple different instances of operating systems at the same time; this technique of virtual machines allows applications to run as if they were on physically distinct computers. In this role, a single mainframe can replace higher-functioning hardware services available to conventional servers.
While mainframes pioneered this capability, virtualization is now available on most families of computer systems, though not always to the same degree or level of sophistication. Mainframes can add or hot swap system capacity without disrupting system function, with specificity and granularity to a level of sophistication not available with most server solutions. Modern mainframes, notably the IBM zSeries, System z9 and System z10 servers, offer two levels of virtualization: logical partitions and virtual machines. Many mainframe customers run two machines: one in their primary data center, one in their backup data center—fully active active, or on standby—in case there is a catastrophe affecting the first building. Test, development and production workload for applications and databases can run on a single machine, except for large demands where the capacity of one machine might be limiting; such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages.
In practice many customers use multiple mainframes linked either by Parallel Sysplex and shared DASD, or with shared, geographically dispersed storage provided by EMC
Microsoft Corporation is an American multinational technology company with headquarters in Redmond, Washington. It develops, licenses and sells computer software, consumer electronics, personal computers, related services, its best known software products are the Microsoft Windows line of operating systems, the Microsoft Office suite, the Internet Explorer and Edge web browsers. Its flagship hardware products are the Xbox video game consoles and the Microsoft Surface lineup of touchscreen personal computers; as of 2016, it is the world's largest software maker by revenue, one of the world's most valuable companies. The word "Microsoft" is a portmanteau of "microcomputer" and "software". Microsoft is ranked No. 30 in the 2018 Fortune 500 rankings of the largest United States corporations by total revenue. Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975, to develop and sell BASIC interpreters for the Altair 8800, it rose to dominate the personal computer operating system market with MS-DOS in the mid-1980s, followed by Microsoft Windows.
The company's 1986 initial public offering, subsequent rise in its share price, created three billionaires and an estimated 12,000 millionaires among Microsoft employees. Since the 1990s, it has diversified from the operating system market and has made a number of corporate acquisitions, their largest being the acquisition of LinkedIn for $26.2 billion in December 2016, followed by their acquisition of Skype Technologies for $8.5 billion in May 2011. As of 2015, Microsoft is market-dominant in the IBM PC-compatible operating system market and the office software suite market, although it has lost the majority of the overall operating system market to Android; the company produces a wide range of other consumer and enterprise software for desktops and servers, including Internet search, the digital services market, mixed reality, cloud computing and software development. Steve Ballmer replaced Gates as CEO in 2000, envisioned a "devices and services" strategy; this began with the acquisition of Danger Inc. in 2008, entering the personal computer production market for the first time in June 2012 with the launch of the Microsoft Surface line of tablet computers.
Since Satya Nadella took over as CEO in 2014, the company has scaled back on hardware and has instead focused on cloud computing, a move that helped the company's shares reach its highest value since December 1999. In 2018, Microsoft surpassed Apple as the most valuable publicly traded company in the world after being dethroned by the tech giant in 2010. Childhood friends Bill Gates and Paul Allen sought to make a business utilizing their shared skills in computer programming. In 1972 they founded their first company, named Traf-O-Data, which sold a rudimentary computer to track and analyze automobile traffic data. While Gates enrolled at Harvard, Allen pursued a degree in computer science at Washington State University, though he dropped out of school to work at Honeywell; the January 1975 issue of Popular Electronics featured Micro Instrumentation and Telemetry Systems's Altair 8800 microcomputer, which inspired Allen to suggest that they could program a BASIC interpreter for the device. After a call from Gates claiming to have a working interpreter, MITS requested a demonstration.
Since they didn't yet have one, Allen worked on a simulator for the Altair while Gates developed the interpreter. Although they developed the interpreter on a simulator and not the actual device, it worked flawlessly when they demonstrated the interpreter to MITS in Albuquerque, New Mexico. MITS agreed to distribute it, marketing it as Altair BASIC. Gates and Allen established Microsoft on April 4, 1975, with Gates as the CEO; the original name of "Micro-Soft" was suggested by Allen. In August 1977 the company formed an agreement with ASCII Magazine in Japan, resulting in its first international office, "ASCII Microsoft". Microsoft moved to a new home in Bellevue, Washington in January 1979. Microsoft entered the operating system business in 1980 with its own version of Unix, called Xenix. However, it was MS-DOS. After negotiations with Digital Research failed, IBM awarded a contract to Microsoft in November 1980 to provide a version of the CP/M OS, set to be used in the upcoming IBM Personal Computer.
For this deal, Microsoft purchased a CP/M clone called 86-DOS from Seattle Computer Products, which it branded as MS-DOS, though IBM rebranded it to PC DOS. Following the release of the IBM PC in August 1981, Microsoft retained ownership of MS-DOS. Since IBM had copyrighted the IBM PC BIOS, other companies had to reverse engineer it in order for non-IBM hardware to run as IBM PC compatibles, but no such restriction applied to the operating systems. Due to various factors, such as MS-DOS's available software selection, Microsoft became the leading PC operating systems vendor; the company expanded into new markets with the release of the Microsoft Mouse in 1983, as well as with a publishing division named Microsoft Press. Paul Allen resigned from Microsoft in 1983 after developing Hodgkin's disease. Allen claimed that Gates wanted to dilute his share in the company when he was diagnosed with Hodgkin's disease because he didn't think he was working hard enough. After leaving Microsoft, Allen lost billions of dollars on ill-conceived or mistimed technology investments.
He invested in low-tech sectors, sports teams, commercial real estate. Despite having begun jointly developing a new operating system, OS/2, with IBM in
The IBM System/370 was a model range of IBM mainframe computers announced on June 30, 1970 as the successors to the System/360 family. The series maintained backward compatibility with the S/360, allowing an easy migration path for customers. In September 1990, the System/370 line was replaced with the System/390; the original System/370 line was announced on June 30, 1970 with first customer shipment of the Models 155 and 165 planned for February 1971 and April 1971 respectively. System/370 underwent several architectural improvements during its 20-year lifetime; the 155 first shipped in January 1971. The first System/370 machines, the Model 155 and the Model 165, incorporated only a small number of changes to the System/360 architecture; these changes included: 13 new instructions, among which wereMOVE LONG. These models did not include support for virtual storage. All models of the System/370 used IBM's form of monolithic integrated circuits called MST making them third generation computers.
MST provided System/370 with four to eight times the circuit density and over ten times the reliability when compared to the previous second generation SLT technology of the System/360. On September 23, 1970, IBM announced the Model 145, a third model of the System/370, which featured monolithic main memory and was scheduled for delivery in the late summer of 1971. All subsequent S/370 models used such memory. In 1972, a significant change was made when support for virtual storage was introduced with IBM's "System/370 Advanced Function" announcement. IBM had chosen to exclude virtual storage from the S/370 line; the August 2, 1972 announcement included: address relocation hardware on all S/370s except the original models 155 and 165 the new S/370 models 158 and 168, with address relocation hardware four new operating systems: DOS/VS, OS/VS1, OS/VS2 Release 1, termed SVS, Release 2, termed MVS and planned to be available 20 months and VM/370 – the re-implemented CP/CMS Virtual storage had in fact been delivered on S/370 hardware before this announcement: In June 1971, on the S/370-145.
The S/370-145 had an associative memory used by the microcode for the DOS compatibility feature from its first shipments in June 1971. Although IBM famously chose to exclude virtual storage from the S/370 announcement, that decision was being reconsidered during the completion of the 145 engineering because of virtual memory experience at CSC and elsewhere; the 145 microcode architecture simplified the addition of virtual storage, allowing this capability to be present in early 145s without the extensive hardware modifications needed in other models. However, IBM did not document the 145's virtual storage capability, nor annotate the relevant bits in the control registers and PSW that were displayed on the operator control panel when selected using the roller switches; the Reference and Change bits of the Storage-protection Keys, were labeled on the rollers, a dead giveaway to anyone who had worked with the earlier 360/67. Existing S/370-145 customers were happy to learn that they did not have to purchase a hardware upgrade in order to run DOS/VS or OS/VS1.
Shortly after the August 2, 1972 announcement, DAT box upgrades for the S/370-155 and S/370-165 were announced, but were available only for purchase by customers who owned a Model 155 or 165. After installation, these models were known as the S/370-155-II and S/370-165-II. IBM wanted customers to upgrade their 155 and 165 systems to the sold S/370-158 and -168; these upgrades were expensive and had long ship date lead times after being ordered by a customer. This led to the original S/370-155 and S/370-165 models being described as "boat anchors"; the upgrade, required to run OS/VS1 or OS/VS2, was not cost effective for most customers by the time IBM could deliver and install it, so many customers were stuck with these machines running MVT until their lease ended. It was not unusual for this to be another four, five or six years for the more unfortunate ones, turned out to be a significant factor in the slow adoption of OS/VS2 MVS, not only by customers in general, but for many internal IBM sites as well.
Architectural changes involved expansions in memory – both physical memory and virtual address space – to enable larger workloads and me
A keyboard layout is any specific mechanical, visual, or functional arrangement of the keys, legends, or key-meaning associations of a computer, typewriter, or other typographic keyboard. Mechanical layout is the keys of a keyboard. Visual layout is the arrangement of the legends. Functional layout is the arrangement of the key-meaning associations, determined in software, of all the keys of a keyboard. Most computer keyboards are designed to send scancodes to the operating system, rather than directly sending characters. From there, the series of scancodes is converted into a character stream by keyboard layout software; this allows a physical keyboard to be dynamically mapped to any number of layouts without switching hardware components – by changing the software that interprets the keystrokes. It is possible for an advanced user to change keyboard operation, third-party software is available to modify or extend keyboard functionality. A computer keyboard consists of alphanumeric or character keys for typing, modifier keys for altering the functions of other keys, navigation keys for moving the text cursor on the screen, function keys and system command keys – such as Esc and Break – for special actions, a numeric keypad to facilitate calculations.
There is some variation between different keyboard models in the mechanical layout – i.e. how many keys there are and how they are positioned on the keyboard. However, differences between national layouts are due to different selections and placements of symbols on the character keys; the core section of a keyboard consists of character keys, which can be used to type letters and other characters. There are three rows of keys for typing letters and punctuation, an upper row for typing digits and special symbols, the Space bar on the bottom row; the positioning of the character keys is similar to the keyboard of a typewriter. Besides the character keys, a keyboard incorporates special keys that do nothing by themselves but modify the functions of other keys. For example, the ⇧ Shift key can be used to alter the output of character keys, whereas the Ctrl and Alt keys trigger special operations when used in concert with other keys. A modifier key is held down while another key is struck. To facilitate this, modifier keys come in pairs, one functionally identical key for each hand, so holding a modifier key with one hand leaves the other hand free to strike another key.
An alphanumeric key labeled with only a single letter can be struck to type either a lower case or capital letter, the latter requiring the simultaneous holding of the ⇧ Shift key. The ⇧ Shift key is used to type the upper of two symbols engraved on a given key, the lower being typed without using the modifier key; the English alphanumeric keyboard has a dedicated key for each of the letters A–Z, along with keys for punctuation and other symbols. In many other languages there are additional letters or symbols, which need to be available on the keyboard. To make room for additional symbols, keyboards have what is a secondary shift key, labeled AltGr, it can be used to type an extra symbol in addition to the two otherwise available with an alphanumeric key, using it with the ⇧ Shift key may give access to a fourth symbol. On the visual layout, these third-level and fourth-level symbols may appear on the right half of the key top, or they may be unmarked. Instead of the Alt and AltGr keys, Apple Keyboards have ⌘ ⌥ Option keys.
The ⌥ Option key is used much like the AltGr, the ⌘ Cmd key like the Ctrl on IBM PCs, to access menu options and shortcuts. Macs have a Ctrl key for compatibility with programs, it is useful when using a terminal, X11 or MS Windows. The key can be used to produce a secondary mouse click as well. There is a Fn key on modern Mac keyboards, used for switching between use of the F1, F2, etc. keys either as function keys or for other functions like media control, accessing dashboard widgets, controlling the volume, or handling exposé. Fn key can be found on many IBM PC laptops, where it serves a similar purpose. Many Unix workstations keyboards placed the Ctrl key to the left of the letter A, the ⇪ Caps Lock key in the bottom left; this layout is preferred by programmers as it makes the Ctrl key easier to reach. This position of the Ctrl key is used on the XO laptop, which does not have a ⇪ Caps Lock; the UNIX keyboard layout differs in the placement of the ESC key, to the left of 1. Some early keyboards experimented with using large numbers of modifier keys.
The most extreme example of such a keyboard, the so-called "Space-cadet keyboard" found on MIT LISP machines, had no fewer than seven modifier keys: four control keys, Meta and Super, along with three shift keys, ⇧ Shift and Front. This allowed the user to type over 8000 possible characters by playing suitable "chords" with many modifier keys pressed simultaneously. A dead key is a special kind of a modifier key that, instead of being held while another key is struck, is pressed and released before the other key; the dead key does not generate a character by itself, but it modifies the character generated by the key struck after making it possible to type a letter with a specific diacritic. For example, on some keyboard layouts, the grave accent key ` is a dead key.