Product Code Database
Hot swapping is the replacement or addition of components to a Computer without stopping, shutting down, or Reboot the system. (2025). 9780080502526, Morgan Kaufmann. ISBN 9780080502526 Hot plugging describes only the addition of components to a running computer system. Components which have such functionality are said to be hot-swappable or hot-pluggable; likewise, components which do not are cold-swappable or cold-pluggable. Although the broader concept of hot swapping can apply to electrical or Machine systems, it is usually mentioned in the context of computer systems.
An example of hot swapping is the express ability to pull a Universal Serial Bus (USB) peripheral device, such as a thumb drive, computer mouse, keyboard, or printer out of a computer's USB slot without powering down the computer first.
Most desktop computer hardware, such as CPUs and memory, are only cold-pluggable. However, it is common for mid to high-end servers and mainframes to feature hot-swappable capability for hardware components, such as CPU, memory, PCI Express, Serial ATA and SAS drives.
Most smartphones and tablets with tray-loading holders can interchange SIM cards without powering down the system.
Dedicated and usually have readily accessible memory card and Electric battery compartments for quick changing with only minimal interruption of operation. Batteries can be cycled through by recharging reserve batteries externally while unused. Many cameras and camcorders feature an internal memory to allow capturing when no memory card is inserted.
Hot swapping is used to add or remove peripherals or components and to replace faulty modules without interrupting equipment operation. For example, a machine may have dual hot-swappable power supply, each adequate enough to power the machine on its own. If one of those power supplies breaks and shuts down, the machine will not shut down, as it will draw power from the other, functional power supply. The faulty power supply can be replaced during operation of the machine, eventually bringing the machine back to a state of redundancy. In the context of servers, important expansion card, such as disk controller or host adapter, may be designed with specialized redundancy features in order for these to be replaceable without necessitating interruption of server operation.
Another use case of hot swapping is to enable faster data synchronization between two devices by not having to power down either device before connecting them together. For example, plugging an iPhone to a Mac computer via a USB cable to synchronize data between them does not require powering down either the iPhone or the Mac and waiting for them to restart. For even more convenience, data synchronization can be configured to start automatically without user input. It is also possible to interrupt the data synchronization at any time simply through unplugging the devices, although it's not recommended to do so until instructed to avoid data corruption.
Additional guide slots, pins, notches, or holes may be used to aid in proper insertion of a component between other live components, while mechanical engagement latches, handles, or levers may be used to assist in proper insertion and removal of devices that either require large amounts of force to connect or disconnect, or to assist in the proper mating and holding together of power and communications connectors.
More complex implementations may recommend but do not require that the component be shut down. In the suboptimal case a component is removed without being shut down, these implementations usually have sufficient redundancy to allow essential operation to continue. In these systems hot swap is normally used for regular maintenance to the computer, or to replace a broken component.
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. Specialized hot-plug power connector pins are now commercially available with repeatable DC current interruption ratings of up to 16 A. Printed circuit boards are made with staggered edge-fingers for direct hot-plugging into a backplane connector.
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, 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 at that speed.
As long as the hot-swap connector is sufficiently rigid, one of the four corner pins will always be the first to engage. 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 center. 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.
A typical sequence for a hot-swap component being plugged into a slot could be as follows:
Hot-swap power circuits can now be purchased commercially in specially designed ASICs called hot-swap power managers (HSPMs).
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 specialized inputs and outputs that minimize 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.
In the mid-1990s, several radio transmitter manufactures in the US started offering swappable high power RF transistor modules.
The reintroduction of power modules has been good for the radio transmitter industry, as it has fostered innovation. Modular transmitters have proven to be more reliable than tube transmitters, when the transmitter is properly chosen for the conditions at the transmitting site.
Power limitations:
Hot-swappable keyboards are becoming increasingly common, and it has become somewhat of a standard in most enthusiast keyboards as well as keyboard components to support hot swapping. They can be found in a variety of sizes and Keyboard layout, including more specialized ergonomic layouts.
Only a few programming languages support hot swapping natively, including Pike, Lisp, Erlang, Smalltalk, Visual Basic 6 (not VB.NET), Java and most recently Elm and Elixir. Microsoft Visual Studio supports a kind of hot swapping called Edit and Continue, which is supported by C#, VB.NET and C/C++ when running under a debugger.
Hot swapping is the central method in live coding, where programming is an integral part of the runtime process. In general, all programming languages used in live coding, such as SuperCollider, TidalCycles, or Extempore support hot swapping.
Some web-based frameworks, such as Django, support detecting module changes and reloading them on the fly. However, although the same as hotswapping for most intents and purposes, this is technically just a cache purge, triggered by a new file. This does not apply to markup and programming languages such as HTML and PHP respectively, in the general case, as these files are normally reinterpreted on each use by default. There are a few CMSes and other PHP-based frameworks (such as Drupal) that employ caching, however. In these cases, similar abilities and exceptions apply.
Hot swapping also facilitates developing systems where large amounts of data are being processed, as in entire genomes in bioinformatics algorithms.
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