ISIS:This article is about the scanning technology. For other meanings see Isis (disambiguation).
ISIS (Image and Scanner Interface Specification) is an industry standard interface for image scanning technologies. It was developed by Pixel Translations in 1990, and they retain control over development and licensing.
ISIS can be considered as a "big brother" to the TWAIN standard, which tends to be used on small scanner hardware for home use.
ISIS compatible scanners typically use a SCSI-2 interface, while TWAIN hardware now mostly uses USB.
ISIS has a wider feature set than TWAIN, can handle greater speeds, and also handles some aspects of image display and manipulation for the client application.
Most major scanner manufacturers, including Kodak, Canon, Hewlett-Packard, and Fujitsu use the ISIS interface for their departmental and high-capacity scanner hardware.
The ISIS architecture is a mutable architecture based on modules—software components that perform specific imaging functions (such as image acquisition, file conversion, data extraction, and file read/write commands). ISIS architecture allows for new modules to be added without making system-wide changes: one simply adds what is needed.
ISIS modules interact with each other through a system of tags (data storage areas) and choices (value sets). A combination of two or more ISIS modules put together to perform a specific imaging function is called an ISIS pipe. ISIS pipes can be constructed according to each developers specific imaging needs.
First and foremost in the benefits ISIS delivers to developers is compatibility: ISIS-compatible drivers are available for more than 250 scanner models, most of them certified by Pixel Translations to be compatible with any properly written ISIS application. ISIS' compatibility is further evidenced by its being the basis for the AIIM (The Association for Information and Image Management) MS61 standard since 1996, which is in the public domain.
External link
- [http://www.pixtran.com/index.asp Pixel Translations]
Category:Imaging
Category:Standards
Isis (disambiguation)Isis was a goddess in Egyptian mythology.
Isis may also refer to:
- HMS Isis, one of several ships in the British Royal Navy
- Morris Isis, a British car
- Isis (band), American metal band
- Isis (Brisbane band), independent rock group
- "Isis" (song), by Bob Dylan and Jacques Levy
- Isis (DC Comics), superhero powered by the Egyptian goddess
- Isis (Image Comics), superhero created by Angel Gate Press and Image Comics
- Isis (Stargate), character in the Stargate TV series
- Isis, the name of the River Thames at Oxford, England
- Isis, the second rowing crew of Oxford University
Places named Isis include:
- Isis, Alexandria (إيزيس), a neighborhood in eastern Alexandria
- Ipswich, Queensland, a city in Australia
- Isisford, Queensland, a town in Australia
- Isis Shire, local government area based around Childers, Queensland, Australia.
- Isis Junction The local train station for Childers, Queensland, Australia
- Isis (Lunar crater), a crater on Earth's moon
- 42 Isis, an asteroid
ISIS may refer to:
- ISIS, document scanner standard
- ISIS (satellite), Canadian ionospheric study satellites
- ISIS Drive, bicycle bottom bracket/crankset interface standard
- ISIS magazine, student magazine at Oxford University
- ISIS neutron source, particle accelerator laboratory in Oxfordshire, UK
- IS-IS, internet communications routing protocol
- ISIS programming language, a dialect of JOSS
- Integrated Scientific Information System, a software program by Elsevier MDL
- ISIS/Draw 2.5, chemical drawing program
- Institute for the Scientific Investigation of Sexuality, authors of the controversial 1983 ISIS Survey
See also
- Isis Unveiled, a book on the occult by Helena Blavatsky
- Fellowship of Isis, a modern religious organization
Image scanner
In computing, a scanner is a device that analyzes a physical image (such as a photograph, printed text, or handwriting) or an object (such as an ornament) and converts it to a digital image.
Most scanners today are variations of the desktop (or flatbed) scanner. Hand-held scanners, where the device is moved by hand, were briefly popular but are now not used due to the difficulty of obtaining a high-quality image. Both these types of scanners use a charge-coupled device (CCD) as the image sensor, whereas a drum scanner uses a photomultiplier tube as the image sensor.
Other types of scanners are planetary scanners, which take photographs of books and documents, and laser range scanners, for producing three-dimensional models of objects.
Drum scanners
laser range scanner
Drum scanners, the oldest scanning technology, have a scanning photomultiplier tube, which moves back and forth along a single axis. The image to be scanned is soaked in oil, then wrapped around the drum; this process is known as dry mounting. The drum then rotates in front of the photomultiplier tube. The use of drum scanners has declined significantly as flatbed scanners based on charge-coupled devices have dropped in price; however, drum scanners are still used for certain high-end applications, such as museum-quality archiving of photographs, desktop publishing, and print production of books and magazines. They are very expensive. Only few companies manufacture them. Due to the fact that a photomultiplier tube is much more sensitive to light than a charge-coupled device and the scanning beam can be focused very narrowly, drum scanners can produce scans superior to those of flatbed scanners, both in resolution and in the gradations of color and brightness. Also, since drum scanners have the advantage for resolution, their use is generally recommended when a scanned image is going to be greatly enlarged.
Physical description
A desktop scanner is usually composed of a glass pane, under which there is a bright light (often xenon or cold cathode fluorescent) which illuminates the pane, and a moving charge-coupled device. Colour scanners typically contain three rows of charge-coupled device elements with red, green, and blue filters. Images to be scanned are placed face down on the glass, the light turns on, and the charge-coupled device and light source move across the pane reading the entire area. An image is therefore visible to the charge-coupled device only because of the light it reflects. Transparent images do not work in this way, and require special accessories that illuminate them from the upper side.
Some models are equipped with an "automatic document feed" or "ADF" feature, which allows the user to place a stack of pages into a hopper, from which each page is automatically fed individually into the scanner. The highly volatile charge-coupled device remains still during automatic document feed scanning, while the page is moved through the scanner by rollers at a constant rate. A separate exit hopper collects the pages after they are scanned.
Scanner quality
Scanners typically read red-green-blue color (RGB) data from the charge-coupled device, process it with some proprietary algorithm to correct for different exposure conditions, and send it to the computer via the device's input/output interface (usually SCSI or USB, or LPT in machines pre-dating the USB standard). Color depth varies depending on the charge-coupled device characteristics, but is usually at least 24 bits. High quality models have 48 bits or more color depth.
The other qualifying parameter for a scanner is its resolution, measured in dots per inch (dpi), sometimes more accurately referred to as samples per inch (spi). Instead of using the scanner's true optical resolution, the only meaningful parameter, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software interpolation. As of 2004, a good flatbed scanner has an optical resolution of 1600–3200 dpi, high-end flatbed scanners can scan up to 5400 dpi, and a good drum scanner has an optical resolution of 8000–14,000 dpi. Manufacturers often claim interpolated resolutions as high as 19,200 dpi; but such numbers carry little meaningful value, because the number of possible interpolated pixels is infinite.
Output data
The final result is a non-compressed RGB image which is typically transferred to a host computer's memory. Such an image can be processed with a raster graphics program (such as Photoshop or the GIMP) and saved on a storage device (such as a hard disk).
Computer connection
The amount of data generated by a scanner can be very large: a 600 DPI 9"x11" (slightly larger A4 paper) uncompressed 24-bit image consumes about 100 megabytes of uncompressed data in transfer and storage on the host computer. Recent scanners can generate this volume of data in a matter of seconds. Therefore, a fast connection is optimal.
Early scanners had parallel connections that could not go faster than 70 kilobytes/second. Professional models adopted the SCSI-II connection, which was much faster (a few megabytes per second) albeit expensive, and frequently requiring a dedicated expansion card to be put inside the host computer.
FireWire, is replacing SCSI as the standard in production (high volume) document scanners.
Recent economic models come equipped with USB connections. In its first version, USB 1.1 was capable of 1.5 megabytes per second. Recent models use USB 2.0 connections that can transfer up to 60 megabytes per second, eliminating the bottleneck.
Two main interface standards exist in the market.
- TWAIN is generally used for low-end and home-use equipment.
- ISIS, created by Pixel Translations, which still uses SCSI-II for performance reasons, is used by large, departmental scale, machines.
Infrared Cleaning
Infrared cleaning is a technique to remove dust and scratches from film. Most modern scanners incorporate this feature. Infrared cleaning works by scanning the film with infrared light. From this, it is possible to detect dust and scratches that cut off the infrared light and they can then be automatically removed based on their position, size, shape and surroundings.
Scanner manufacturers usually have their own name attached to this technique. For example, Epson, Nikon, Microtek and others use [http://www.asf.com/products/ice/FilmICEOverview.shtml Digital ICE] developed by Kodak, while Canon uses its own [http://www.canon.com/technology/scan/02.html FARE] (Film Automatic Retouching and Enhancement) system.
External links
- [http://www.scantips.com ScanTips.com]
- [http://www.michaelpapet.com/shome.htm Digital Imaging Guy] - description of the factors involved in scanner quality
- [http://www.digitaloutput.net/content/ContentCT.asp?P=431 Is Drum Scanning Really Alive and Well?] from Digital Output
- [http://www.kenrockwell.com/tech/scantek.htm Photo Scanner Technology Explained] by Ken Rockwell
- [http://www.luminous-landscape.com/reviews/scanners/drum_scans.shtml about drum scanners]
- [http://www.microtekusa.com] - Scanner Specialists and Pioneers
- [http://www.twain.org twain.org]
- [http://www.sane-project.org sane project]
Category:Input devices
Category:Office equipment
ja:イメージスキャナ
SCSISCSI stands for "Small Computer System Interface", and is a standard interface and command set for transferring data between devices on both internal and external computer buses. SCSI is usually pronounced "scuzzy".
SCSI is most commonly used for hard disks and tape storage devices, but also connects a wide range of other devices, including scanners, CD-ROM drives, CD recorders, and DVD drives. In fact, the entire SCSI standard promotes device independence, which means that theoretically anything can be made SCSI — SCSI printers have been manufactured.
Since its standardization in 1986, SCSI has been commonly used in the Apple Macintosh and Sun Microsystems computer lines. It has never been popular in the IBM PC world, due to the lower cost and adequate performance of its ATA hard disk standard. The introduction of USB, FireWire, and ATAPI made SCSI a relatively unattractive proposition on PC due to its high cost and rising complexity.
At this time, SCSI is popular on high-performance workstations, servers, and high-end peripherals; and RAID arrays on servers almost always use SCSI hard disks. Desktop computers and notebooks more typically use the ATA/IDE or the newer SATA interfaces for hard disks, and USB or FireWire connections for external devices.
History
In 1979, Shugart Associates introduced an interface called SASI (Shugart Associates System Interface). At the same time, NCR Corporation's Peripherals division (now Engenio), had developed a more sophisticated product called BYSE, and was developing an ASIC to implement it. In late 1981, NCR and Shugart agreed to merge the best features of the two solutions, and to jointly promote the concept as an ANSI standard. After several committee meetings and after a number of other companies decided to adopt the combined standard, it received the new name "SCSI." In 1986, with SCSI already in widespread use, ANSI approved the SCSI spec (as X3.131-1986). Since then, SCSI has developed as an industry-wide standard, capable of being applied to virtually any computer system (there were even SCSI implementations for the venerable Commodore 64 and Apple II home computers). The first working SCSI ASIC was donated by NCR to the Smithsonian Museum.
Standards
SCSI has the unfortunate distinction of having among the most confusing set of standards names of anything in the computer field, with the probable exception of 3D video cards. There are a dozen SCSI interface names, most with ambiguous wording (Quick, which is faster: Wide SCSI or Fast SCSI?); three SCSI standards, each of which has a collection of modular, optional features; several different connector types; and three different types of voltage signalling. The leading SCSI card manufacturer, Adaptec, has manufactured over 100 varieties of SCSI cards over the years.
SCSI has evolved since its introduction. Before summarizing the evolution, a distinction should be made between the terminology used in the SCSI standard itself, as promulgated by the T10 committee of INCITS, and common parlance, as codified by the SCSI trade association, SCSITA.
As of 2003, there have only been three SCSI standards: SCSI-1, SCSI-2, and SCSI-3. All SCSI standards have been modular, defining various capabilities which manufacturers can include or not. Individual vendors and SCSITA have given names to specific combinations of capabilities. For example, the term "Ultra SCSI" is not defined anywhere in the standard, but is used to refer to SCSI implementations that signal at twice the rate of "Fast SCSI." Such a signalling rate is not compliant with SCSI-2 but is one option allowed by SCSI-3. Similarly, no version of the standard requires low-voltage-differential (LVD) signalling, but products called Ultra-2 SCSI include this capability. This terminology is helpful to consumers, because "Ultra-2 SCSI" device has a better-defined set of capabilities than simply identifying it as "SCSI-3."
Starting with SCSI-3, the SCSI standard has been maintained as a loose collection of standards, each defining a certain piece of the SCSI architecture, and bound together by the SCSI Architectural Model. This change divorces SCSI's various interfaces from the command set, allowing devices that support SCSI commands to use any interface (including ones not otherwise specified by T10), and also allowing the interfaces that are defined by T10 to develop on their own terms. This change is also why there is no "SCSI-4".
No version of the standard has ever specified what kind of connector should be used. The connectors used by vendors have tended to evolve over time. Although SCSI-1 devices typically used bulky Blue Ribbon ("Centronics") connectors, and SCSI-2 devices typically "Mini-D" connectors, it is not correct to refer to these as "SCSI-1" and "SCSI-2" connectors.
The mainstream implementations of SCSI (in chronological order) are as follows, using common parlance:
SCSI-1
The original standard that was derived from SCSI and formally adopted in 1986 by ANSI. SCSI-1 features an 8-bit bus (with parity), running asynchronously at 3.5 MB/s or 5 MB/s in synchronous mode, and a maximum bus cable length of 6 meters (just under 20 feet -- compare that to the 18 inch (0.45 meter) limit of the ATA interface). A variation on the original standard included a high-voltage differential (HVD) implementation whose maximum cable length was many times that of the single-ended versions.
SCSI-2
This standard was introduced in 1989 and gave rise to the Fast SCSI and Wide SCSI variants. Fast SCSI doubled the maximum transfer rate to 10 MB/s and Wide SCSI doubled the bus width to 16 bits on top of that (to reach 20 MB/s). However, these improvements came at the minor cost of a reduced maximum cable length to 3 meters. SCSI-2 also specified a 32-bit version of Wide SCSI, which used 2 16-bit cables per bus; this was largely ignored by SCSI device makers because it was expensive and unnecessary, and was officially retired in SCSI-3.
SCSI-3
Before Adaptec and later SCSITA codified the terminology, the first parallel SCSI devices that exceeded the SCSI-2 capabilities were simply designated SCSI-3. These devices, also known as Ultra SCSI and fast-20 SCSI, were introduced in 1992. The bus speed doubled again to 20 MB/s for narrow (8 bit) systems and 40 MB/s for wide. The maximum cable length stayed at 3 meters but ultra SCSI developed an undeserved reputation for extreme sensitivity to cable length and condition (faulty cables, connectors or terminators were often to blame for instability problems).
Ultra-2
This standard was introduced c. 1997 and featured a low voltage differential (LVD) bus. For this reason ultra-2 is sometimes referred to as LVD SCSI. Using LVD technology, it became possible to allow a maximum bus cable length of 12 meters (almost 40 feet!), with much greater noise immunity. At the same time, the data transfer rate was increased to 80 MB/s. Ultra-2 SCSI actually had a relatively short lifespan, as it was soon superseded by ultra-3 (ultra-160) SCSI.
Ultra-3
Also known as Ultra-160 SCSI and introduced toward the end of 1999, this version was basically an improvement on the ultra-2 standard, in that the transfer rate was doubled once more to 160 MB/s by the use of double transition clocking. Ultra-160 SCSI offered new features like cyclic redundancy check (CRC), an error correcting process, and domain validation.
Ultra-320
This is the ultra-160 standard with the data transfer rate doubled to 320 MB/s. Nearly all new SCSI hard drives being manufactured at the time of this writing (October 2003) are actually ultra-320 devices.
Ultra-640
Ultra-640 (otherwise known as Fast-320) was promulgated as a standard (INCITS 367-2003 or SPI-5) in early 2003. Ultra-640 doubles the interface speed yet again, this time to 640 MB/s. Ultra640 pushes the limits of LVD signaling; the speed limits cable lengths drastically, making it impractical for more than one or two devices. Because of this, most manufacturers have skipped over Ultra640 and are developing for Serial Attached SCSI instead.
iSCSI
iSCSI preserves the basic SCSI paradigm, especially the command set, almost unchanged. iSCSI advocates project the iSCSI standard, an embedding of SCSI-3 over TCP/IP, as displacing Fibre Channel in the long run, arguing that Ethernet data rates are currently increasing faster than data rates for Fibre Channel and similar disk-attachment technologies. iSCSI could thus address both the low-end and high-end markets with a single commodity-based technology.
Serial SCSI
Three recent versions of SCSI SSA, FC-AL and Serial Attached SCSI break from the traditional parallel SCSI standards and perform data transfer via serial communications.
SCSI command protocol
In additon to all the different hardware implementations, the SCSI standards also include a complex set of protocol definitions.
In SCSI terminology, communication takes place between an initiator and a target. The initiator sends a command to the target which then responds. SCSI commands are sent in a Command Descriptor Block (CDB). Each CDB can be a total of 6, 10, 12, or 16 bytes, but later versions of the SCSI standard also allow for variable-length CDBs. The CDB consists of a one byte operation code followed by some command-specific parameters.
At the end of the command the target returns a code byte 00h for success, 02h for an error (called a Check Condition), or 08h for busy. When a SCSI target device returns a check condition in response to a command, the initiator usually then issues a SCSI Request Sense command in order to obtain a Key Code Qualifier (KCQ) from the target.
There are 4 categories of SCSI commands: N (non-data), W (writing data from initiator to target), R (reading data), and B (bidirectional). There are about 60 different SCSI commands in total, with the most common being:
- Test unit ready - "ping" the device to see if it responds
- Inquiry - return basic device information
- Send diagnostic - the device performs a self-test and returns the result
- Request sense - give any error codes from the previous command
- Read capacity - return storage capacity
- Format Unit
- Read (4 variants)
- Write (4 variants)
- Write and verify
- Mode select - set device parameters, held in a number of mode pages
- Mode sense - return current device parameters
Each device on the SCSI bus is assigned at least one logical unit number (LUN). In some more complex implementations (such as storage virtualization) one physical device may behave as if it is many separate LUNs. A storage device consists of a number of logical blocks, usually referred to by the term Logical Block Address (LBA). A typical LBA equates to 512 bytes of storage.
The addressing scheme for LBAs has evolved over time and so four different command variants are provided for reading and writing data. The Read(6) and Write(6) commands contain a 21-bit LBA address. The Read(10), Read(12), Read Long, Write(10), Write(12), and Write Long commands all contain a 32-bit LBA address plus various other parameter options.
SCSI bus operation
This section relates only to parallel SCSI buses (although similar sequences occur on serial SCSI buses).
All SCSI commands start with a process called arbitration when one or more devices attempt to access the bus. During the arbitration phase, the 8 or 16 data bus signals are used to identify which device(s) are requesting access. All SCSI devices must implement the same arbitration algorithm so the result is always unamimous. The parallel SCSI bus goes through 8 phases as a command is processed:
- Bus-free
- Arbitration - one or more devices assert BSY and their ID bit
- Selection - one device wins the arbitration by asserting BSY and SEL
- Command - the initiator sends the CDB to the target
- Data - direction of transfer depends on the command
- Message - SCSI message code - interface management information
- Status - SCSI status byte - success or failure information
- Bus-free
The arbitration process can use up a lot of bus bandwidth so more recent devices support a simplified protocol called Quick Arbitration and Selection (QAS).
Compatibility
Note: Ultra-2, ultra-160 and ultra-320 devices may be freely mixed on the LVD bus with no compromise in performance, as the host adapter will negotiate the operating speed and bus management requirements for each device. Single-ended devices should not be attached to the LVD bus, as doing so will force all devices to run at the slower single-ended speed. Support for single-ended interfaces has been deprecated in the SPI-5 standard (which describes Ultra-640), so future devices may not be electrically backward compatible.
Caution: Modern Single Connector Attachment (SCA) devices may be connected to older controller/drive chains by using SCA adapters. Although these adapters often have auxiliary power connectors, use caution: it is possible to quickly destroy the drive by connecting external power. Always try the drive without auxiliary power first.
SCSI devices are generally backward-compatible, i.e., it is possible to connect an ultra-3 SCSI hard disk to an ultra-2 SCSI controller and use it (though with reduced speed and feature set).
Each SCSI device (including the computer's host adapter) must be configured to have a unique SCSI ID on the bus. Also, the SCSI bus must be terminated with a terminator. Both active and passive terminators are in common use, with the active type much preferred (and required on LVD buses). Improper termination is a common problem with SCSI installations.
It is possible to convert a wide bus to a narrow one, with widedevices closer to the adapter. To do this properly requires a cable which terminates the wide part of the bus. This is sometimes referred to as a cable with high-9 termination. Specific commands allow the host to determine the active width of the bus. This arrangement is discouraged.
SCSI IDs
All devices on a parallel SCSI bus must have a SCSI ID. The initiator (controller) SCSI ID is usually set by a physical jumper or switch. The target (disk-drive) SCSI IDs are either set by physical jumpers or by control signals which vary for each connector in an enclosure.
The SCSI ID is a 3-bit value for 8-bit wide buses and a 4-bit value for 16-bit wide buses. The priority sequence for an 8-bit wide SCSI bus is: 7 (highest), 6, 5, 4, 3, 2, 1, 0 (lowest). The priority sequence for a 16-bit wide SCSI bus has to meet legacy requirements so is less obvious: 7 (highest), 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8 (lowest). The SCSI ID of the initiator is usually set to the highest priority value of 7. If there are two initators then their SCSI IDs are usually set to 7 and 6. All the remaining unused SCSI IDs can then used for disk-drives or other storage devices.
SCSI IDs are used in the arbitration process to determine which device next gets access to the SCSI bus. If two devices attempt to access the bus at the same time then the one with the highest priority SCSI ID will win the arbitration. During the arbitration process, the 8 or 16 data bus signals are used to determine which device(s) are requesting arbitration.
Termination
Parallel SCSI buses must always be terminated at both ends to ensure reliable operation.
A positive voltage is provided by one or more devices on the bus, typically the initiator(s). This positive voltage is called TERMPOWER and is usually around +4.3 volts. TERMPOWER is normally generated by a diode connection to +5.0 volts. This is called a diode-OR arrangement.
Some early disk drives included internal terminators, but most modern disk-drives do not provide termination which is then deemed to be external.
Termination can be passive or active. Passive termination means that each signal line is terminated by two resistors, 220 Ohms to TERMPOWER and 330 Ohms to ground. Active termination means that there is a small voltage regulator which provides a +3.3V supply. Each signal line is then terminated by a 110 Ohm resistor to the +3.3V supply.
In current practice most parallel SCSI buses are LVD and so require external, active termination. The usual termination circuit consists of a +3.3V linear regulator and commercially available SCSI resistor network devices (not individual resistors).
See [http://www.scsita.org/aboutscsi/termTutorial.html Termination Tutorial].
External links
- [http://www.t10.org/ T10 Technical Committee - SCSI Storage Interfaces ] (SCSI standards)
- [http://www.scsita.org/terms/scsiterms.html SCSITA terminology]
- [http://www.bswd.com/cornucop.htm "Storage Cornucopia" SCSI links, maintained by a consultant]
- [http://home.nc.rr.com/woodsmall/SCSI.htm SCSI/iSCSI/RAID/SAS Information Sheet]
- [http://www.pcnineoneone.com/howto/scsi1.html SCSI basics]
- [http://www.scsilibrary.com/ WWW Virtual Library for SCSI]
Category:SCSI
Category:Computer storage
Category:Computing acronyms
Category:Macintosh internals
Category:Computer buses
ja:SCSI
USB:For other meanings of the abbreviation USB see USB (disambiguation).
USB (disambiguation)
USB (disambiguation)
USB (disambiguation)
Universal Serial Bus (USB) provides a serial bus standard for connecting devices, usually to a computer, but it also is in use on other devices such as set-top boxes, game consoles such as Sony's PlayStation 2, Microsoft's Xbox 360, Nintendo's Revolution and PDAs.
Overview
A USB system has an asymmetric design, consisting of a host controller and multiple devices connected in a tree-like fashion using special hub devices. There is a limit of 5 levels of branching hubs per controller. Up to 127 devices may be connected to a single host controller, but the count must include the hub devices as well. A modern computer likely has several host controllers so the total useful number of connected devices is beyond what could reasonably be connected to a single controller. There is no need for a terminator on any USB bus, as there is for SPI-SCSI and some others.
The design of USB aimed to remove the need for adding separate expansion cards into the computer's ISA or PCI bus, and improve plug-and-play capabilities by allowing devices to be hot swapped or added to the system without rebooting the computer. When the new device first plugs in, the host enumerates it and loads the device driver necessary to run it.
device driver
USB can connect peripherals such as mice, keyboards, gamepads and joysticks, scanners, digital cameras, printers, hard disks, and networking components. For multimedia devices such as scanners and digital cameras, USB has become the standard connection method. For printers, USB has also grown in popularity and started displacing parallel ports because USB makes it simple to add more than one printer to a computer. As of 2004 there were about 1 billion USB devices in the world. As of 2005, the only large classes of peripherals that cannot use USB (because they need a higher data rate than USB can provide) are displays and monitors, data acquisition devices that use firewire ports, and high-quality digital video components.
Standardization
The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Apple Computer, Hewlett-Packard, NEC, Microsoft, Intel, and Agere.
The USB specification is at version 2.0 as of January 2005. Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips jointly led the initiative to develop a higher data transfer rate than the 1.1 specification to meet the bandwidth demands of developing technologies. The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Previous notable releases of the specification were 0.9, 1.0, and 1.1. Each iteration of the standard is completely backward compatible with previous versions.
Smaller USB plugs and receptors called Mini-A and Mini-B are also available, as specified by the On-The-Go Supplement to the USB 2.0 Specification. The specification is of revision 1.0a currently.
Technical details
2001
USB connects several devices to a host controller through a chain of hubs. In USB terminology devices are referred to as functions, because in theory what we know as a device may actually host several functions, such as a router that is a Secure Digital Card reader at the same time. The hubs are special purpose devices that are not officially considered functions. There always exists one hub known as the root hub, which is attached directly to the host controller.
These devices/functions (and hubs) have associated pipes (logical channels) which are connections from the host controller to a logical entity on the device named an endpoint. The pipes are synonymous to byte streams such as in the pipelines of Unix, however in USB lingo the term endpoint is (sloppily) used as a synonym for the entire pipe, even in the standard documentation.
These endpoints (and their respective pipes) are numbered 0-15 in each direction, so a device/function can have up to 32 active pipes, 16 inward and 16 outward. (The OUT direction shall be interpreted out of the host controller and the IN direction is into the host controller.) Endpoint 0 is however reserved for the bus management in both directions and thus takes up two of the 32 endpoints. In these pipes, data is transferred in packets of varying length. Each pipe has a maximum packet length, typically bytes, so a USB packet will often contain something on the order of 8, 16, 32, 64, 128, 256, 512 or 1024 bytes.
Each endpoint can transfer data in one direction only, either into or out of the device/function, so each pipe is uni-directional. All USB devices have at least two such pipes/endpoints: namely endpoint 0 which is used to control the device on the bus. There is always an inward and an outward pipe numbered 0 on each device. The pipes are also divided into four different categories by way of their transfer type:
- control transfers - typically used for short, simple commands to the device, and a status response, used e.g. by the bus control pipe number 0
- isochronous transfers - at some guaranteed speed (often but not necessarily as fast as possible) but with possible data loss, e.g. realtime audio or video
- interrupt transfers - devices that need guaranteed quick responses (bounded latency), e.g. pointing devices and keyboards
- bulk transfers - large sporadic transfers using all remaining available bandwidth (but with no guarantees on bandwidth or latency), e.g. file transfers
When a device (function) or hub is attached to the host controller through any hub on the bus, it is given a unique 7 bit address on the bus by the host controller. The host controller then polls the bus for traffic, usually in a round-robin fashion, so no device can transfer any data on the bus without explicit request from the host controller.
To access an endpoint, a hierarchical configuration must be obtained. The device connected to the bus has one (and only one) device descriptor which in turn has one or more configuration descriptors. These configurations often correspond to states, e.g. active vs. low power mode. Each configuration descriptor in turn has one or more interface descriptors, which describe certain aspects of the device, so that it may be used for different purposes: for example, a camera may have both audio and video interfaces. These interface descriptors in turn have one default interface setting and possibly more alternate interface settings which in turn have endpoint descriptors, as outlined above. An endpoint may however be reused among several interfaces and alternate interface settings.
The hardware that contains the host controller and the root hub has an interface toward the programmer which is called Host Controller Device (HCD) and is defined by the hardware implementer. In practice, these are hardware registers (ports) in the computer.
At version 1.0 and 1.1 there were two competing HCD implementations. Compaq's Open Host Controller Interface (OHCI) was adopted as the standard by the USB-IF. However, Intel subsequently created a specification they called the Universal Host Controller Interface (UHCI) and insisted other implementers pay to license and implement UHCI. VIA Technologies licensed the UHCI standard from Intel; all other chipset implementers use OHCI. The main difference between OHCI and UHCI is the fact that UHCI is more software-driven than OHCI is, making UHCI slightly more processor-intensive but cheaper to implement (excluding the license fees). The dueling implementations forced operating system vendors and hardware vendors to develop and test on both implementations which increased cost. During the design phase of USB 2.0 the USB-IF insisted on only one implementation. The USB 2.0 HCD implementation is called the Extended Host Controller Interface (EHCI). Only EHCI can support high-speed transfers. Each EHCI controller contains four virtual HCD implementations to support Full Speed and Low Speed devices. The virtual HCD on Intel and Via EHCI controllers are UHCI. All other vendors use virtual OHCI controllers.
On Microsoft Windows platforms, one can tell whether a USB port is version 2.0 by opening the Device Manager and checking for the word "Enhanced" in its description; only USB 2.0 drivers will contain the word "Enhanced." On Linux systems, the lspci command will list all PCI devices, and a controllers will be named OHCI, UHCI or EHCI respectively, which is also the case in the Mac OS X system profiler.
Device classes
Devices that attach to the bus can be full-custom devices requiring a full-custom device driver to be used, or may belong to a device class. These classes define an expected behaviour in terms of device and interface descriptors so that the same device driver may be used for any device that claims to be a member of a certain class. An operating system is supposed to implement all device classes so as to provide generic drivers for any USB device. The most used device classes are:
- USB human interface device class, keyboards, mice, etc.
- USB mass storage device class used for keydrives, portable hard drives, Multi Media Card readers, digital cameras, digital audio players etc. This device class presents the device as a block device (almost always used to store a file system).
- USB communications device class ("CDC") used for modems (and winmodems), network cards (and cross-over cables), ISDN connections, Fax
- USB printer device class, printer-like devices
- USB audio device class, sound card-like devices
- USB video device class, webcam-like devices, motion image capture devices
Device classes are decided upon by the Device Working Group of the USB Implementers Forum.
USB signaling
Standard USB signaling
webcam
USB signals are transmitted on a twisted pair of data cables, labelled D+ and D−. These collectively use half-duplex differential signaling to combat the effects of electromagnetic noise on longer lines. D+ and D− operate together; they are not separate simplex connections.
Transfer speed
USB supports three data rates.
- A Low Speed rate of 1.5 Mbit/s (183 KiB/s) that is mostly used for Human Interface Devices (HID) such as keyboards, mice and joysticks.
- A Full Speed rate of 12 Mbit/s (1.4 MiB/s). Full Speed was the fastest rate before the USB 2.0 specification and many devices fall back to Full Speed. Full Speed devices divide the USB bandwidth between them in a first-come first-served basis and it is not uncommon to run out of bandwidth with several isochronous devices. All USB Hubs support Full Speed.
- A Hi-Speed rate of 480 Mbit/s (57 MiB/s). (Commonly called USB 2.0)
Not all USB 2.0 devices are Hi-Speed. A USB device should specify the speed it will use by correct labeling on the box it came in or sometimes on the device itself. The USB-IF certifies devices and provides licenses to use special marketing logos for either "Basic-Speed" (low and full) or High-Speed after passing a compliancy test and paying a licensing fee.
Hi-Speed devices should fall back to the slower data rate of Full Speed when plugged into a Full Speed hub. Hi-Speed hubs have a special function called the Transaction Translator that segregates Full Speed and Low Speed bus traffic from Hi-Speed traffic. The Transaction Translator in a Hi-Speed hub (or possibly each port depending on the electrical design) will function as a completely separate Full Speed bus to Full Speed and Low Speed devices attached to it. This segregation is for bandwidth only; bus rules about power and hub depth still apply.
Mini USB signaling
USB-IF
Most of the pins of a mini USB connector are the same as a standard USB connector, except pin 4. Pin 4 is called ID and is connected to pin 5 for a mini-A and is either unconnected or connected to pin 5 through a resistor for a mini-B.
USB connectors
The connectors which the USB committee specified were designed to support a number of USB's underlying goals, and to reflect lessons learned from the varied menagerie of connectors then in service. In particular:
- The connectors are designed to be robust. Many previous connector designs were fragile, with pins or other delicate components prone to bending or breaking, even with the application of only very modest force. The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is further protected by an enclosing metal sheath. As a result USB connectors can safely be handled, inserted, and removed, even by a small child. The encasing sheath and the tough moulded plug body mean that a connector can be dropped, stepped upon, even crushed or struck, all without damage; a considerable degree of force is needed to significantly damage a USB connector.
- It is difficult to incorrectly attach a USB connector. Connectors cannot be plugged-in upside down, and it is clear from the appearance and kinesthetic sensation of making a connection when the plug and socket are correctly mated.
- The connectors are particularly cheap to manufacture.
- The connectors enforce the directed topology of a USB network. USB does not support cyclical networks, so the connectors from incompatible USB devices are themselves incompatible. Unlike other communications systems (e.g. RJ-45 cabling) gender-changers are never used, making it difficult to create a cyclic USB network.
- A moderate insertion/removal force is specified. USB cables and small USB devices are held in place by the gripping force from the receptacle (without the need for the screws, clips, or thumbturns other connectors require). The force needed to make or break a connection is modest, allowing connections to be made in awkward circumstances or by those with motor disabilities.
- The connector construction always ensures that the external sheath on the plug contacts with its counterpart in the receptacle before the four connectors within are connected. This sheath is typically connected to the system ground, allowing otherwise damaging static charges to be safely discharged by this route (rather than via delicate electronic components). This means of enclosure also means that there is a (moderate) degree of protection from electromagnetic interference afforded to the USB signal while it travels through the mated connector pair (this is the only location when the otherwise twisted data pair must travel a distance in parallel).
- The USB standard specifies relatively low tolerances for compliant USB connectors, intending to minimize incompatibilities in connectors produced by different vendors (a goal that has been very successfully achieved). Unlike most other connector standards, the USB spec also defines limits to the size of a connecting device in the area around its plug. This was done to avoid circumstances where a device complied with the connector specification but its large size blocked adjacent ports. Compliant devices must either fit within the size restrictions or support a compliant extension cable which does.
The USB 1.0, 1.1 and 2.0 specifications define two types of connectors for the attachment of devices to the bus: A, and B. However, the mechanical layer has changed in some examples. For example, the IBM UltraPort is a proprietary USB connector located on the top of IBM's laptop LCDs. It uses a different mechanical connector while preserving the USB signaling and protocol. Other manufacturers of small items also developed their own small form factor connector, and a wide variety of these have appeared. For specification purposes, these devices were treated as having a captive cable.
An extension to USB called USB On-The-Go allows a single port to act as either a host or a device - chosen by which end of the cable plugs into the socket on the unit. Even after the cable is hooked up and the units are talking, the two units may "swap" ends under program control. This facility targets units such as PDAs where the USB link might connect to a PC's host port as a device in one instance, yet connect as a host itself to a keyboard and mouse device in another instance. USB On-The-Go has therefore defined two small form factor connectors, the mini-A and mini-B, and a hermaphroditic socket (mini-AB), which should stop the proliferation of proprietary designs.
Wireless USB is a promising future standard being developed to extend the USB standard while maintaining backwards compatibility with USB 1.1 and USB 2.0 on the protocol level.
The maximum length of a USB cable is 5 meters; greater lengths require hubs [http://www.usb.org/developers/usbfaq/#cab1].
Power supply
The USB connector provides a single nominally 5 volt wire from which connected USB devices may power themselves. In practice, delivered voltage can drop well below 5 V, to only slightly above 4 V. The compliance spec requires no more than 5.25 V anywhere and no less than 4.375 V at the worst case; a low-power function after a bus-powered hub. In typical situations the voltage is close to 5 V.
A given segment of the bus is specified to deliver up to 500 mA. This is often enough to power several devices, although this budget must be shared among all devices downstream of an unpowered hub. A bus-powered device may use as much of that power as allowed by the port it is plugged into.
Bus-powered hubs can continue to distribute the bus provided power to connected devices but the USB specification only allows for a single level of bus-powered devices from a bus-powered hub. This disallows connection of a bus-powered hub to another bus-powered hub. Many hubs include external power supplies which will power devices connected through them without taking power from the bus. Devices that need more than 500 mA must provide their own power.
When USB devices (including hubs) are first connected they are interrogated by the host controller, which enquires of each their maximum power requirements. The host operating system typically keeps track of the power requirements of the USB network and may warn the computer's operator when a given segment requires more power than is available (and will generally shut down devices or hubs in order to keep power consumption within the available resource).
A number of devices use this power supply without participating in a proper USB network. The typical example is a USB-powered reading light, but fans, battery chargers (particularly for mobile telephones) and even miniature vacuum cleaners are available. In most cases, these items contain no electronic circuitry, and thus are not proper USB devices at all. This can cause problems with some computers—the USB specification requires that devices connect in a low-power mode (100 mA maximum) and state how much current they need, before switching, with the host's permission, into high-power mode.
Some devices intended for connection to laptops draw more power than is permitted by the specification for a single USB port; to avoid requiring an exernal power supply, these devices come with dual cables, and the user is instructed that the device must be plugged-into two USB ports. On a laptop with only two ports, this means only one such device can be used at a time, unless a powered hub is added. A number of peripherals for IBM laptops (now made by Lenovo) are designed to use dual USB connections in this manner.
USB-powered devices attempting to draw large currents without requesting the power will not work with certain USB controllers, and will either disrupt other devices on the bus or fail to work themselves (or both). Those problems with the abuse of the USB power supply have inspired a number of April Fool hoaxes, like the introduction of a USB-powered George Foreman iGrill [http://www.thinkgeek.com/stuff/looflirpa/igrill.shtml] and a desktop USB Fondue Set [http://www.thinkgeek.com/stuff/41/fundue.shtml].
USB compared to other standards
Storage
Fondue
USB implements connections to storage devices using a set of standards called the USB mass-storage device class. This was initially intended for traditional magnetic and optical drives, but has been extended to support a wide variety of devices. USB is not intended to be a primary bus for a computer's internal storage: buses such as ATA (IDE) and SCSI fulfill that role.
However, USB has one important advantage in making it possible to install and remove devices without opening the computer case, making it useful for external drives. Today, a number of manufacturers offer portable USB hard drives that offer performance comparable to conventional ATA (IDE) drives. These external drives, called enclosures, are often composed of translating devices that connect to USB on one side and to conventional IDE, ATA, ATAPI, or SCSI drives on the other. A drive is installed into the enclosure and the enclosure is then plugged into the computer, thus creating the function of a regular USB mass-storage device.
FireWire technology is also commonly used with portable hard drives, some of which include both USB and FireWire ports. FireWire tends to perform better in speed benchmark tests. However, USB ports are more common on consumer-level computers, which enhances the portability of a USB drive.
Human-interface devices (HIDs)
USB has not completely replaced AT keyboard connections and PS/2 keyboard and mouse connections, but virtually all PC motherboards manufactured today have one or more USB ports. As of 2004, most new motherboards have multiple USB 2.0 high-speed ports, though some are internal, and require a "header" connection to be accessible from the front or rear of the computer case. Similarly, support for joysticks, keypads, tablets and other human-interface devices is progressively migrating from MIDI, "game", and PS/2 connectors to USB. It is now quite common for a mouse or keyboard to be a USB device, which is shipped with a small USB-to-PS/2 adaptor connected to the end of its cable, so it can be used with either USB or PS/2 ports.
Apple computers have used USB mice and keyboards exclusively since January 1999.
USB 2.0 vs FireWire
USB 2.0 transmits data at up to 480 megabits per second (Mbps) while FireWire 400 (IEEE 1394a) handles data at up to 400 Mbps [http://www.choice.com.au/viewArticle.aspx?id=104527&catId=100274&tid=100008&p=1]. However USB 2.0 is not commonly considered to be faster than FireWire 400. USB uses more CPU resources than FireWire and its data transfer rate is degraded as more load is applied to the CPU (by running concurrent tasks). Finally, the more recent IEEE 1394b specification of FireWire supports data rates up to 3.2 gigabits per second.
Version history
USB
- USB 1.0 FDR: Released in November 1995, the same year that Apple adopted the IEEE 1394 standard known as FireWire.
- USB 1.0: Released in January 1996.
- USB 1.1: Released in September 1998.
- USB 2.0: Released in April 2000. The major feature of this standard was the addition of high-speed mode. This is the current revision.
- USB 2.0: Revised in December 2002. Added three speed distinction to this standard, allowing all devices to be USB 2.0 compliant even if they were previously considered only 1.1 or 1.0 compliant. The makes the backwards compatibility explicit, but more difficult to determine a device's throughput without seeing the symbol. As an example, a computer's port could be incapable of USB 2.0's hi-speed fast transfer rates, but still claim USB 2.0 compliance (since it supports some of USB 2.0).
USB On-The-Go Supplement
- USB On-The-Go Supplement 1.0: Released in December 2001.
- USB On-The-Go Supplement 1.0a: Released in June 2003. This is the current revision.
Extensions to USB
The PictBridge standard allows for interconnecting consumer imaging devices. It typically uses USB as the underlying communication layer.
Microsoft's Xbox game console uses standard USB 1.1 signalling, but features a proprietary connector rather than the standard USB connector. Similarly IBM UltraPort uses standard USB signalling, but uses a proprietary connection format.
The USB Implementers Forum is working on a wireless networking standard based on the USB protocol. Wireless USB is intended as a cable-replacement technology, and will use Ultra wideband wireless technology for data rates of up to 480 Mbit/s. Wireless USB is well suited to wireless connection of PC centric devices, just as Bluetooth is now widely used for mobile phone centric personal networks (at much lower data rates). See http://www.usb.org/developers/wusb/ for more details.
See also
- ACCESS.bus
- FireWire (also known as IEEE 1394, or I.link)
- USB Flash Drive
- USB streaming
- U3
- Serial cable (obsoleted by USB and Wi-Fi)
External links
- [http://www.usb.org/ Home of USB Implementers Forum, Inc.], including [http://www.usb.org/developers/docs/ the USB 2.0 specification]
- [http://www.lvr.com/usb.htm USB Central] for developers of USB devices and hosts
- [http://www.bootdisk.com/usb.htm USB for DOS]
- [http://www.linux-usb.org/ Linux USB Project], containing much technical information and documentation
- [http://www.windowsnetworking.com/articles_tutorials/usbmain.html USB Networking Introduction]
- [http://usbmount.alioth.debian.org/ Linux usbmount].
- [http://www.beyondlogic.org/usbnutshell/usb-in-a-nutshell.pdf USB in a NutShell] - a primer for developers
- [http://developer.intel.com/technology/usb/uhci11d.htm Universal Host Controller Interface (UHCI)]
Category:Computer buses
Category:USB
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KodakEastman Kodak.
Canon (company)
Canon Inc. , (in Japanese: キヤノン株式会社) is a Japanese company that is headquartered in Tokyo, Japan that specializes in imaging and optical products, including cameras, photocopiers and computer printers.
The company was founded in 1933 with the name 精機光学研究所 (Seiki-kougaku-kenkyuujo or Precision Optical Instruments Laboratory) by the co-founder Yoshida Goro and his brother-in-law Uchida Saburo, funded by Takeshi Mitarai, a close friend of Uchida. Its original purpose was to research into the development of quality cameras. In June 1934 they released their first camera, the Kwanon, named after the Buddhist goddess of mercy. The following year the company name was changed to Canon in a more modern reflection of the name.
The company's first cameras were Leica threadmount rangefinder clones. They closely followed the Leica specifications for the threadmount lens (M39) but added innovations including a switchable magnification combined viewfinder/rangefinder. Canon at first did not have its own optical factory, so they used lenses made by Nikon. But they soon started to make their own lenses under the Serenar brand. These lenses remain popular even now by users of Canon or Leica rangefinders.
Despite the company's high profile in the consumer market for cameras and computer printers, most of the company revenue comes from the office products division, especially for analog and digital copiers, and its line of imageRUNNER digital multifunctional devices. Canon has also entered the digital displays market by teaming up with Toshiba to develop and manufacture flat panel televisions based on SED, a new type of display technology. Canon has also announced its intention to enter the projection television market as well.
The official Japanese name of the company is キヤノン (kiyanon) not キャノン (kyanon): see the [http://www.canon.jp company home page] for confirmation.
Canon's main competitors include Nikon, Konica Minolta, Leica, Pentax, Olympus, Sony, Epson, Kodak, Lomo, Hewlett-Packard and Xerox.
See also
- List of Canon products
External links
- [http://www.canon.com/ Canon official site]
Category:Electronics companies
Category:Electronics companies of Japan
ja:キヤノン
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Fujitsu:For the district in Saga, Japan, see Fujitsu, Saga.
Fujitsu (富士通) is a Japanese company specializing in semiconductors, computers (supercomputers, personal computers, servers), telecommunications, and services, and is headquartered in Tokyo. Fujitsu Limited reported consolidated revenues of 5.00 trillion yen for the fiscal year which ended March 31, 2002.
The company was established in 1935 under the name Fuji Tsūshinki Seizō (富士通信機製造, Fuji Telecommunications Equipment Manufacturing), a spinoff of the Fuji Electric Company, this in turn being a joint venture between the Furukawa Electric Company and German conglomerate Siemens. Despite its connections to the Furukawa zaibatsu, Fujitsu escaped the Allied occupation of Japan mostly unscathed.
By 1954 Fujitsu had rolled out Japan's first computer, the FACOM 100, and seven years later its transistorized big brother FACOM 222 joined the fray. In 1967, the company's name was officially changed to the contraction Fujitsū (富士通).
Today Fujitsu, the communications spinoff of the electric spinoff of a mining company, employs some 200,000 people and has another 500 subsidiary companies itself. The active partnership with Siemens AG has been
revived in the form of Fujitsu Siemens Computers (est. 1999), Europe's largest IT supplier owned 50/50 by Fujitsu and Siemens. Internationally, Fujitsu considers IBM to be its main competitior. Its historical domestic rival is NEC. Major acquisitions include UK-based International Computers Ltd (ICL) and US-based Amdahl.
See also
- Kawasaki Frontale
- FM Towns
External links
- [http://www.fujitsu.com/global/ Fujitsu Global]
- [http://pr.fujitsu.com/en/profile/history/hist1.html Company history]
Category:Electronics companies
Category:Computer hardware companies
Category:Electronics companies of Japan
ja:富士通
Category:ImagingFor more information, refer to the article on imaging.
Category:Image processing
Category:Computer vision
Category:StandardsCategory:Reference
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