Hot swapping or hot plugging is the ability to remove and replace components of a machine, usually a computer, while it is operating. Once the appropriate software is installed on the computer, a user can plug and unplug the component without rebooting. A well-known example of this functionality is the Universal Serial Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard, or printer. It usually requires more sophisticated software and hardware than does plug-and-play. The NASA Columbia Supercomputer. ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. ... Universal Serial Bus (USB) is a serial bus standard to interface devices. ... Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ...

History

Historically, only expensive systems could hot-swap components as it was very difficult to engineer correctly. However, the technology has become commonplace in recent years and even low-end computer systems support it.

Protocols that now support hot swapping include PC card, USB, FireWire, Fibre Channel, SATA, SCSI and SAS. Protocols that do not support hot swapping include PATA and PS/2. Hot-swap components can include anything from USB flash drives to server hard drives, or PCI-X expansion cards (PCI-X is usually only in servers), PCMCIA cards (PC Cards) used in laptops, and even some power supplies. The PCMCIA is the Personal Computer Memory Card International Association, an industry trade association that creates standards for notebook computer peripheral devices. ... Universal Serial Bus (USB) is a serial bus standard to interface devices. ... The 6-pin and 4-pin FireWire Connectors FireWire is Apple Inc. ... This article or section does not adequately cite its references or sources. ... A SATA power connector. ... This article or section does not cite any references or sources. ... 2. ... ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ... The PS/2 connector is used for connecting a keyboard and a mouse to a PC compatible computer system. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... For other meanings of PCI, see PCI (disambiguation). ... A wall wart style variable DC power supply with its cover removed. ...

System considerations

Machines that support hot swapping need some ability to detect that a component has been removed. In addition, all electrical and mechanical connections need to be designed such that neither the component nor the user can be harmed by removing it. Lastly, other components in the system must be designed such that the removal of a different component does not harm operation. Often there is some automatic recovery process.

Some implementations require a component shut-down procedure prior to removal. This simplifies the design, but such devices are not robust in the case of component failure. If a component is removed while it is being used, the operations to that device fail and the user is responsible for retrying if necessary. As this action is normally done by end-users this is not considered a problem. These hot swap operations are generally used either to move a peripheral component from one computer to another, or to allow a device to synchronize data with a computer. For an account of the words periphery and peripheral as they are used in biology, sociology, politics, computer hardware, and other fields, see the periphery disambiguation page. ...

More complex implementations may recommend that the component be shut down, but there is sufficient redundancy in the system such that if a component is removed without being shut down, operation continues. In these systems hot swap is normally used for regular maintenance to the computer, or to replace a broken component. In engineering, the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe, is called redundancy. ...

There are two slightly differing meanings of the term hot swapping. In some contexts, it refers only to the ability to add or remove hardware without powering down the system, while in other contexts, it refers to the system's ability to autonomously detect when hardware is added or removed. In the former case, one can add or remove hardware without powering down, but the system software may have to be notified of the event in order to use the new hardware. Examples of the former include RS-232, FireWire and lower-end SCSI devices, while examples of the latter include USB, FireWire and higher-end SCSI devices. When comparing these two cases, it is common to only refer to the latter case as true hotplugging, and call the former case coldplugging. RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... This article or section does not cite any references or sources. ... This article or section does not cite any references or sources. ... Coldplugging is often taken to mean the opposite of hotplugging. ...

Connectors

Sun SPARCstation hot swappable SCA drive cradle

Most modern hot-swap methods rely on a specialised connector with staggered pins. At one time staggered pins were thought to be an expensive solution, but many contemporary connector families now come with staggered pins as standard. For example, they are used on all modern serial SCSI disk-drives. Specialised hot-plug power connector pins are now commercially available with repeatable DC current interruption ratings of up to 16 A. Printed circuit boards can be designed for direct hot-plugging onto a backplane, with staggered edge-fingers providing the same results as staggered connector pins. Image File history File linksMetadata Size of this preview: 800 × 504 pixelsFull resolution (2034 × 1281 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 504 pixelsFull resolution (2034 × 1281 pixel, file size: 1. ... Staggered Pin Grid Array or SPGA is a style of socket used on some integrated circuits, usually CPUs. ... Part of a 1983 Sinclair ZX Spectrum computer board. ...

Most staggered pin designs have the ground pins longer than all the other pins. This ensures that any sensitive circuitry is never connected before there is a reliable system ground. The rest of the connector might be made up of short pins, or in some cases there can be a total of three different pin-lengths.

Although the speed of plugging cannot be controlled precisely, practical considerations will provide limits that can be used to determine worst-case conditions. For a typical staggered pin design where the length difference is 0.5 mm (0.020 inches), the elapsed time between long and short pin contact is between 25 ms and 250 ms. It is quite practical to design hot-swap circuits that can operate over that dynamic range. Note that pins of the same nominal length do not make contact at exactly the same time due to mechanical tolerances.

As long as the hot-swap connector is sufficiently rigid, one of the four corners will always be first to make physical contact with the slot. For a typical two-row connector arrangement this provides four first-to-make corner pins that are usually used for grounds. Other pins near the corners can be used for functions that would also benefit from this effect, for example sensing when the connector is fully seated. This diagram illustrates good practice where the grounds are in the corners and the power pins are near the centre. Two sense pins are located in opposite corners so that fully seated detection is confirmed only when both of them are in contact with the slot. The remaining pins are used for all the other data signals. Image File history File links No higher resolution available. ...

Power electronics

The DC power supplies to a hot-swap component are usually pre-charged by dedicated long pins that make contact before the main power pins. These pre-charge pins are protected by a circuit that limits the inrush current to an acceptable value that cannot damage the pins nor disturb the supply voltage to adjacent slots. The pre-charge circuit might be a simple series resistor, a Negative Temperature Coefficient (NTC) resistor, or a current-limiter circuit. Further protection can be provided by a "soft-start" circuit that provides a managed ramp-up of the internal DC supply voltages within the component.

A typical sequence for a hot-swap component being plugged into a slot could be as follows:

1. Long ground pins make contact - Basic electrical safety and ESD protection becomes available
2. Long (or medium) pre-charge pins make contact - Decoupling capacitors start to charge up
3. Realtime delay of tens of milliseconds
4. Short power/signal pins make contact
5. Connector becomes fully seated - Power-on reset signal asserted within component
6. Soft-start circuit starts to apply power to the component
7. Realtime delay of tens of milliseconds
8. Soft-start circuit completes sequence - Power-on reset circuit deasserted
9. Component begins normal operation

Hot-swap power circuits can now be purchased commercially in specially designed ASICs called Hot Swap Power Managers (HSPMs). This article does not cite any references or sources. ...

Signal electronics

Circuitry attached to signal pins in a hot-swap component should include some protection against ElectroStatic Discharge (ESD). This usually takes the form of clamp diodes to ground and to the DC power supply voltage. ESD effects can be reduced by careful design of the mechanical package around the hot-swap component, perhaps by coating it with a thin film of conductive material. ESD can refer to: Electrostatic discharge Electronic services delivery Enlightened Sound Daemon (also known as EsounD or ESD) English as a second dialect Electronic Software Distribution Ecologically Sustainable Development Electro_Sun_Dog, a character on FurryMUCK portrayed as an anthromorphic Basenji Category: ...

Particular care must be taken when designing systems with bussed signals which are wired to more than one hot-swap component. When a hot-swap component is inserted its input and output signal pins will represent a temporary short-circuit to ground. This can cause unwanted ground-level pulses on the signals which can disturb the operation of other hot-swap components in the system. This was a problem for early parallel SCSI disk-drives. One common design solution is to protect bussed signal pins with series diodes or resistors. CMOS buffer devices are now available with specialised inputs and outputs that minimise disturbance of bussed signals during the hot-swap operation. If all else fails, another solution is to quiesce the operation of all components during the hot-swap operation. Parallel SCSI is a computer term used to describe one of the physical implementations of SCSI communications. ...

Software

Hot swapping can also refer to the ability to alter the running code of a program without having to interrupt its execution, although only a few languages support it. Those that do include Lisp, Erlang, Smalltalk, Java, C#, and VB.NET; the last two only support hot swapping when run under a debugger. Using hotswap organizations with long running Web servers are able to fix bugs without taking down the server program. It also facilitates the development of Bioinformatics algorithms where large amounts of data such as entire genomes are being processed. Interactive programming is a paradigm that makes extensive use of hot swapping so that the programming activity becomes part of the program flow itself. Lisp is a family of computer programming languages with a long history and a distinctive fully-parenthesized syntax. ... Erlang is a general-purpose concurrent programming language and runtime system. ... Smalltalk is a dynamically typed object oriented programming language designed at Xerox PARC by Alan Kay, Dan Ingalls, Ted Kaehler, Adele Goldberg, and others during the 1970s. ... Java is a programming language originally developed by Sun Microsystems and released in 1995. ... The title given to this article is incorrect due to technical limitations. ... Visual Basic . ... Interactive Programming vs. ...

Plug in a device while the computer is running Host swapping

• Coldplug

Bold text Coldplugging is often taken to mean the opposite of hotplugging. ...

External links

• Hotplug support in Linux-based systems
• Datasheet for high current hot-swap connector pin
• Datasheet for HSPM hot-swap ASIC
• Datasheet for hot-swap CMOS logic family