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59-547: There were four series of machines, starting with the original DECwriter in 1970, the DECwriter II in 1974, DECwriter III in 1978, and the final DECwriter IV in 1982. The first three were physically similar, large machines mounted on a stand normally positioned above a box of fanfold paper . They differed primarily in speed and the selection of computer interfaces. The IV was significantly different, intended for desktop use and looking more like an IBM Selectric typewriter than

118-618: A message-based protocol for communicating with their devices—as user-mode drivers. If such drivers malfunction, they do not cause system instability. The Kernel-Mode Driver Framework (KMDF) model continues to allow development of kernel-mode device drivers, but attempts to provide standard implementations of functions that are known to cause problems, including cancellation of I/O operations, power management, and plug and play device support. Apple has an open-source framework for developing drivers on macOS , called I/O Kit. In Linux environments, programmers can build device drivers as parts of

177-597: A 33 by 18 dot matrix that reduced the printing rate to 30 cps. As before, the LA100 was offered as the print-only Letterprinter 100 or a variety of Letterwriter 100 terminals. The internal character set ROM was further expanded to support the British, Finnish, French, Canadian French, German, Italian, Norwegian/Danish, Spanish, and Swedish character sets. More interesting was the addition of plug-in ROM cartridges containing

236-502: A complete 128-character ASCII set, including upper and lower case as well as various control characters . The character set was stored in read only memory (ROM), and optional ROMs for Katakana and the APL symbols were also available. The 63-key keyboard followed the ANSI X4.14-1971 typewriter layout, and included a further 19 keys for numeric input and various controls. The tractor feed

295-536: A high percentage of the mail being discarded without being read. A decollator separates multi-part continuous form paper into separate stacks of one-part continuous form paper and may also remove the carbon paper. A burster is a machine that separates one-part continuous form paper into separate, individual, sheets along the transverse perforations. A burster was typically used with printed continuous form paper applications such as mass-mail advertising, invoices, and account statements. The machine has two sets of rollers;

354-487: A high-level application for interacting with a serial port may simply have two functions for "send data" and "receive data". At a lower level, a device driver implementing these functions would communicate to the particular serial port controller installed on a user's computer. The commands needed to control a 16550 UART are much different from the commands needed to control an FTDI serial port converter, but each hardware-specific device driver abstracts these details into

413-437: A target for exploits . Bring Your Own Vulnerable Driver (BYOVD) uses signed, old drivers that contain flaws that allow hackers to insert malicious code into the kernel. Drivers that may be vulnerable include those for WiFi and Bluetooth, gaming/graphics drivers, and drivers for printers. There is a lack of effective kernel vulnerability detection tools, especially for closed-source OSes such as Microsoft Windows where

472-618: A tractor feed mechanism, which could also be purchased separately for the LA34. Both fed paper in from the top, like a typewriter, and did not need any room below them for paper feeding. The LA34 was not as suited for unattended printing of large volumes of data, since its friction feed was more prone to tracking skew and paper jams than its tractor feed siblings. The DECwriter IV series also introduced optional support for DEC's sixel graphics format, allowing it to produce black and white graphics output. This worked by sending characters using only 6 of

531-652: A traditional printer. Most models were available without a keyboard for print-only usage, in which case they were later known as DECprinter s. The DECwriters were among DEC's best-selling products, notably the II and III series. The original DECwriter was introduced in November 1970 at the Fall Joint Computer Conference. Also known by its model number, LA30 , it was one of the earliest dot matrix printers to be introduced to market, only months after

590-563: Is important that the hardware manufacturer provide information on how the device communicates. Although this information can instead be learned by reverse engineering , this is much more difficult with hardware than it is with software. Microsoft has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, called Windows Driver Frameworks (WDF). This includes User-Mode Driver Framework (UMDF) that encourages development of certain types of drivers—primarily those that implement

649-407: Is improved stability, since a poorly written user-mode device driver cannot crash the system by overwriting kernel memory. Because of the diversity of modern hardware and operating systems, drivers operate in many different environments. Drivers may interface with: Common levels of abstraction for device drivers include: So choosing and installing the correct device drivers for given hardware

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708-400: Is necessary the perforations can be much finer, leaving an almost perfectly smooth edge (microperforations, microperf for short). Continuous form paper of all types remains in production, although largely supplanted with the introduction of fast laser printers with single-sheet feed. Continuous stationery printed on a suitable printer is typically cheaper than laser printing although the output

767-532: Is of lower quality. If an impact printer is used multiple simultaneous copies can be printed on multipart forms. Many laser printers can print on both sides of the paper (duplex printing), which is not possible with continuous stationery. Standard perforations are 5/32 inch in diameter (3.96875 mm, sometimes called 4 mm) and are spaced at 1 ⁄ 2 inch (13 mm) center-to-center. Tear-off horizontal perforations at page top/bottom are exactly in-between standard perforations, at whatever regular interval

826-472: Is often a key component of computer system configuration. Virtual device drivers represent a particular variant of device drivers. They are used to emulate a hardware device, particularly in virtualization environments, for example when a DOS program is run on a Microsoft Windows computer or when a guest operating system is run on, for example, a Xen host. Instead of enabling the guest operating system to dialog with hardware, virtual device drivers take

885-563: Is still available in the US from large retailers of office supplies such as OfficeMax and Staples . Device driver In the context of an operating system , a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton . A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about

944-508: Is that they can be loaded only when necessary and then unloaded, thus saving kernel memory. Depending on the operating system, device drivers may be permitted to run at various different privilege levels . The choice of which level of privilege the drivers are in is largely decided by the type of kernel an operating system uses. An operating system which uses a monolithic kernel , such as the Linux kernel , will typically run device drivers with

1003-403: Is used for that particular paper. When the perforated edges of the paper are manufactured so that they tear off the pages in strips, those strips are known as "perfory." The highest grade of continuous form paper uses a heavy bond weight similar to typing paper. Perforations are very small and close together, referred to as microperforations or microperf, to allow the sheets to be separated and

1062-417: Is used in some of the fastest types of printing systems, some of which print text at a rate of 20,000 lpm (lines per minute). This will produce about 400 pages per minute, using about 8–11 large boxes of paper for every hour of printing (affected by character density, and other details such as paper weight). Direct mail, as an industry overall, has been accused of being environmentally unfriendly, due to

1121-400: Is via protection rings . On many systems, such as those with x86 and ARM processors, switching between rings imposes a performance penalty, a factor that operating system developers and embedded software engineers consider when creating drivers for devices which are preferred to be run with low latency, such as network interface cards . The primary benefit of running a driver in user mode

1180-612: The PCI bus or USB is identified by two IDs which consist of two bytes each. The vendor ID identifies the vendor of the device. The device ID identifies a specific device from that manufacturer/vendor. A PCI device has often an ID pair for the main chip of the device, and also a subsystem ID pair that identifies the vendor, which may be different from the chip manufacturer. Computers often have many diverse and customized device drivers running in their operating system (OS) kernel which often contain various bugs and vulnerabilities , making them

1239-405: The interrupt handling required for any necessary asynchronous time-dependent hardware interface. The main purpose of device drivers is to provide abstraction by acting as a translator between a hardware device and the applications or operating systems that use it. Programmers can write higher-level application code independently of whatever specific hardware the end-user is using. For example,

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1298-529: The kernel , separately as loadable modules , or as user-mode drivers (for certain types of devices where kernel interfaces exist, such as for USB devices). Makedev includes a list of the devices in Linux, including ttyS (terminal), lp ( parallel port ), hd (disk), loop, and sound (these include mixer , sequencer , dsp , and audio). Microsoft Windows .sys files and Linux .ko files can contain loadable device drivers. The advantage of loadable device drivers

1357-681: The 8 bits of the printable character set and using those six bits to directly control six of the seven pins in the print head. This way, graphics data could be sent efficiently over 7-bit links. The printer could be commanded to expand the data horizontally to several different characters-per-inch settings. Otherwise similar to the IV series, the LA100 series used a nine-pin print head and offered three different printing speeds to provide what DEC referred to as draft, memo, or letter qualities. In draft mode it printed at 240 cps, while in letter quality it used

1416-480: The IV series in features. Fanfold paper Continuous stationery (UK) or continuous form paper (US) is paper which is designed for use with dot-matrix and line printers with appropriate paper-feed mechanisms. Other names include fan-fold paper , sprocket-feed paper , burst paper , lineflow (New Zealand), tractor-feed paper , and pin-feed paper . It can be single-ply (usually woodfree uncoated paper ) or multi-ply (either with carbon paper between

1475-629: The IV series were small desktop systems that looked like contemporary electric typewriters , notably the IBM Selectric . They were slow, at 30 cps, and were not intended as outright replacements for the III series, which were more suited to unattended computer-room console terminal operation. Two models were offered, the LA34 which used a typewriter-like roller feed mechanism, and the LA38 which added

1534-842: The LA12X-AL add-on kit provided a current loop interface for those who still needed it, while the LA12X-BB added parallel interface, and the LA12X-CB connected to the Unibus . The LA12X-DL option expanded the character buffer to 4 kB. The first complete redesign of the DECwriter line was introduced in June 1982 with the DECwriter IV . In contrast to the earlier models, which were large standalone units on their own floor-standing pedestals,

1593-650: The LA30, and was physically similar although smaller and more rectangular. Like the LA30, the LA36 was also offered in a keyboard-less printer-only model, in this case known as the LA35 . The primary change was the addition of a data buffer that allowed it to store characters. This meant the terminal could continue accepting data from the host computer while the printer was performing carriage returns or other time-consuming operations, and then resume printing without loss of data. When

1652-454: The RA but able to print on up to nine-thick copy paper as opposed to the normal six-thick of the base model. The LA120's were similar to the earlier models mechanically, with only minor changes to the layout of the printer and the floor stand. Internally, the primary change was the addition of a 1 kB character buffer, which allowed it to store many lines of text. The printer electronics examined

1711-404: The actual glyph data for the characters. The system could support two plug-in cartridges and as many as three internal ROMs (bare chips), to allow up to five character sets at a time. The LA12 DECwriter Correspondent was a small form-factor terminal for portable use, weighing 20 pounds (9.1 kg). Various models offered built-in modems or other interfaces. The system was otherwise similar to

1770-549: The data, skipping over blank areas at high speed, and optimizing printing in both directions by reading backward through the buffer where appropriate. The overall speed increased to 180 cps. In addition to the character sets of the II series, the III added new character sets with National Replacement Character Sets for Finland, Denmark, Sweden, Germany, Norway, and France. It also offered eight options for character width (narrow or wide) and double-strike for bold. The LA120s normally were supplied with only an RS-232 interface, but

1829-681: The design of their hardware. Moreover, it was traditionally considered in the hardware manufacturer 's interest to guarantee that their clients can use their hardware in an optimal way. Typically, the Logical Device Driver (LDD) is written by the operating system vendor, while the Physical Device Driver (PDD) is implemented by the device vendor. However, in recent years, non-vendors have written numerous device drivers for proprietary devices, mainly for use with free and open source operating systems . In such cases, it

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1888-744: The engagement hole strips. Common sizes in North America: In Europe, both 11 and 12-inch (279 and 305 mm) form heights were common, the latter closely approaching the A4 standard sheet size (297 mm, 11.7 in). Printing on continuous forms was at one time the basis for many business operations, not the least of which the direct mail industry. Reader's Digest and Publisher's Clearing House relied heavily on these forms to promote their products (most often via sweepstakes), issue billing, address form letter correspondence, and manage their own business data needs. Continuous form paper

1947-445: The explicit goal of "having been designed to replace the standard Teletype Model 33, 35 and 37 KSR". The LA30 used a 64-character ASCII -based character set , lacking lower-case characters and printing them in upper-case. It used a 7-pin print head with glyphs in a 5x7 grid. It normally printed 80-column lines on standard 9 + 7 ⁄ 8 inch wide tractor feed paper. It could print up to 30 characters per second (cps), matching

2006-424: The first (infeed) runs at a given speed, the second (outfeed) located a specific distance away, running at a higher speed. The first form is gripped by the infeed roller and moves under the second roller. Due to the higher speed, the forms is stretched taut, forcing the perforation against a knife, thus separating the form from the continuous form. The continuous form paper then advances into the feed rollers to burst

2065-663: The general public in the 1980s due to the development of microcomputers and inexpensive dot-matrix consumer printers. Continuous form paper began to disappear from the consumer market in the 1990s as desktop publishing , and WYSIWYG document generation became more popular and widespread. Consumers were willing to pay more to get a laser printer or inkjet printer that could produce near-typeset-quality documents. These printers accept standard size cut sheets ( letter , legal or A4) of paper and do not require continuous form paper. Continuous form paper continues to be used in specialty commercial and industrial markets and, as of 2021,

2124-461: The hardware being used. A driver communicates with the device through the computer bus or communications subsystem to which the hardware connects. When a calling program invokes a routine in the driver, the driver issues commands to the device (drives it). Once the device sends data back to the driver, the driver may invoke routines in the original calling program. Drivers are hardware dependent and operating-system-specific. They usually provide

2183-629: The introduction of the DECwriter III , or LS120 . This was a cost-reduced and improved version of the LA36 that supported only serial input out of the box, lacking the former current loop interface. Three new versions based on the LS120 were introduced in November 1978, the print-only LA120-RA DECprinter III , the LA120-DA which replaced the LA36 terminal, and the LA120-RB , otherwise similar to

2242-406: The maximum interface speed of 300 bit/s (30 cps, assuming one start and one stop bit). The interface could also run at 110 and 150 bit/s. However, carriage returns required 1 ⁄ 3 of a second, during which time the host computer had to send data it would know would not be printed, the so-called " fill characters " that were commonly required by printers of the era. Mechanically, the machine

2301-637: The new name for the port, EIA-232. A later addition was the LA30-P , the "P" referring to the addition of a parallel Centronics port , which had become an almost universal de facto standard by the mid-1970s. A replacement for the original product line was announced in August 1974 with the introduction of the DECwriter II series and its first model, the LA36 . The LA36 used the same basic printing mechanism as

2360-428: The next sheet. Bursting is often a high-speed process that allows the continuous form paper to feed in at a steady rate, with burst pages either stacked or fed into a single-sheet conveyance to the next paper processing stage. Burster equipment and paper manufactures had to generate perforation specifications so that the paper perforations reliably separated under the force of pulling the sheets apart and not tear down into

2419-446: The opposite role and emulates a piece of hardware, so that the guest operating system and its drivers running inside a virtual machine can have the illusion of accessing real hardware. Attempts by the guest operating system to access the hardware are routed to the virtual device driver in the host operating system as e.g.,  function calls . The virtual device driver can also send simulated processor-level events like interrupts into

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2478-491: The paper layers, or multiple layers of carbonless copy paper ), often described as multipart stationery or forms. Continuous stationery is often used when the final print medium is less critical in terms of the appearance at the edges, and when continuously connected individual sheets are not inconvenient for the application. Individual sheets can be separated at the perforation (leaving a slight serration), and sheets also have edges with punched holes, which also can be removed at

2537-456: The perforation (one typical format). Most continuous form paper is punched longitudinally along both edges with regularly spaced engagement holes that engage with sprocket wheels or toothed belts on the "tractor" which move the paper through the printer. It is usually perforated transversely with a line of closely spaced holes or slits which form a tear edge that allows it to be torn neatly into separate pages after printing; when fed through

2596-406: The print head fell behind, it began printing characters as fast as possible until the buffer was empty again, at speeds as high as 60 cps. This had the added advantage that the host computer did not have to insert fill characters, which in turn led to simpler interfacing requirements and reduced device driver complexity. There were numerous other changes as well. The character set now included

2655-464: The printed part of the sheet. Large continuous documents might not be split into separate sheets. By continuously folding two single sided printed sheets back-to-back and binding together a stack of continuous form paper along one of the folded edges, it is possible to flip through the stack like a book of double-sided printed pages. With this technique, the stack is normally flipped top to bottom or bottom to top rather than side to side. This paper type

2714-592: The printer the paper is simply a continuous sheet. After printing the separated sheets can be held in binders by using the sprocket holes when simply required as a record. Alternatively some types of continuous form paper also have longitudinal perforations along each edge inside the engagement holes, allowing the strips with sprocket holes to be torn off the printed page. The tear perforations may be short slits, which leave noticeable serrations when torn apart, acceptable for many business documents such as invoices or basic data (such as computer code). Where better appearance

2773-513: The printing mechanism, both for basic maintenance and for feeding in new paper. DEC suggested leaving 16 inches (410 mm) behind the system to provide enough room to swing it fully open. In June 1972, DEC introduced two new versions of the DECwriter, the LA30A which lacked a keyboard and was used as a dedicated printer, and the LA30-E which added an RS-232 interface option, the "E" standing for

2832-410: The rest of the system. Even drivers executing in user mode can crash a system if the device is erroneously programmed . These factors make it more difficult and dangerous to diagnose problems. The task of writing drivers thus usually falls to software engineers or computer engineers who work for hardware-development companies. This is because they have better information than most outsiders about

2891-499: The same (or similar) software interface. Writing a device driver requires an in-depth understanding of how the hardware and the software works for a given platform function. Because drivers require low-level access to hardware functions in order to operate, drivers typically operate in a highly privileged environment and can cause system operational issues if something goes wrong. In contrast, most user-level software on modern operating systems can be stopped without greatly affecting

2950-509: The same privilege as all other kernel objects. By contrast, a system designed around microkernel , such as Minix , will place drivers as processes independent from the kernel but that use it for essential input-output functionalities and to pass messages between user programs and each other. On Windows NT , a system with a hybrid kernel , it is common for device drivers to run in either kernel-mode or user-mode . The most common mechanism for segregating memory into various privilege levels

3009-525: The seminal Centronics 101 that May at the Spring Joint Computer Conference. At the time, most small computer systems were accessed using surplus or new teletype units, such as the popular ASR-33 . The LA30 was intended to be used in the same general fashion (although it lacked any ability to read or output punched tape ). As such, its only computer interface was a 30 mA current loop , as used on teletype machines, with

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3068-452: The source code of the device drivers is mostly not public (open source) and drivers often have many privileges. A group of security researchers considers the lack of isolation as one of the main factors undermining kernel security , and published an isolation framework to protect operating system kernels, primarily the monolithic Linux kernel whose drivers they say get ~80,000 commits per year. An important consideration in

3127-467: The sprocket hole strip ("perfory," see "Shape and Form" section) torn off leaving a very smooth edge almost as if guillotine -cut. The cheapest grade of continuous form paper is often preprinted with bars of light green lines across its width, to facilitate following a line of information across the page, a type commonly referred to as green bar , music or music-ruled paper. It is a very lightweight bond, usually without slit perforations to remove

3186-418: The systems even more functionality. The Intertec Superdec offered 1200 bit/s support, double-wide characters, APL characters, and even user-defined character sets. The Datasouth DS120 was similar, lacking the character sets but adding bidirectional printing. The Selanar Graphics II add-on offered bitmapped graphics support as well as increased speeds to 9,600 bit/s. The DECprinter I , model LA180 ,

3245-451: The virtual machine. Virtual devices may also operate in a non-virtualized environment. For example, a virtual network adapter is used with a virtual private network , while a virtual disk device is used with iSCSI . A good example for virtual device drivers can be Daemon Tools . There are several variants of virtual device drivers, such as VxDs , VLMs , and VDDs. Solaris descriptions of commonly used device drivers: A device on

3304-496: Was 2 by 2 feet (0.61 by 0.61 m) and came mounted on robust legs that raised the keyboard to standard desk height with the top 31 inches (790 mm) from the ground. Normally, a box of fanfold paper would be placed below the printer mechanism and feed upward though a slot in the bottom of the stand. The casing around the keyboard was curved, somewhat similar to the ADM-3A . The entire front cover lifted upward to provide access to

3363-418: Was developed for use with autographic registers around 1910, was later adopted by tabulating machines beginning in the 1920s, and its use grew with the introduction of commercial computers in the 1950s. IBM cards , preprinted, optionally numbered and pre-punched, were available as continuous form cards and were used for checks and other documents. Continuous form paper became widely used and well known to

3422-547: Was introduced in September 1976. This was essentially a simplified version of the LA35, offered only with a Centronics port to provide speeds up to 180 cps. In November, the same basic mechanism was used as the basis for new versions of the LA35 and LA36, differing primarily in using serial ports which made them easier to connect to DEC systems. These models went on to become one of DEC's best-selling products. January 1977 saw

3481-455: Was much more flexible, with a horizontally-fixed pin-drive on the left and an adjustable one on the right, allowing it to feed paper from 3 to 14.875 inches (76.2 to 377.8 mm) wide and to print up to 132 columns. The print head had enough force to print through six pieces of paper, allowing it to print using carbon paper or copy paper forms. The teleprinters were so popular that several third party companies introduced add-on cards to give

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