Hot swapping

Last updated
Hot-swapping a hard drive in a storage server IBM TotalStorage Exp400.jpg
Hot-swapping a hard drive in a storage server

Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; [1] hot plugging describes the addition of components only. [2] 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.

Contents

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, PCIe, SATA and SAS drives.

An example of hot swapping is the express ability to pull a Universal Serial Bus (USB) peripheral device, such as a thumb drive, external hard disk drive (HDD), mouse, keyboard, or printer out of a computer's USB slot or peripheral hub without ejecting it first.

Most smartphones and tablets with tray-loading holders can interchange SIM cards without powering down the system.

Dedicated digital cameras and camcorders usually have readily accessible memory card and 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.

Rationale

Hot swapping is used whenever it is desirable to change the configuration or repair a working system without interrupting its operation. [3] It may simply be for convenience of avoiding the delay and nuisance of shutting down and then restarting complex equipment or because it is essential for equipment, such as a server, to be continuously active.

Hot swapping may be used to add or remove peripherals or components, to allow a device to synchronize data with a computer, and to replace faulty modules without interrupting equipment operation. A machine may have dual power supplies, each adequate to power the machine; a faulty one may be hot-swapped. Important cards such as disk controllers or host adapters may be designed with redundant paths in order for these to be replaceable in case of failure without necessitating interruption of associated computer system operation.

System considerations

Machines that support hot swapping need to be able to modify their operation for the changed configuration, either automatically on detecting the change, or by user intervention. All electrical and mechanical connections associated with hot-swapping must be designed so that neither the equipment nor the user can be harmed while hot-swapping. Other components in the system must be designed so that the removal of a hot-swappable component does not interrupt operation.

Mechanical design

Protective covering plates, shields, or bezels may be used on either the removable components or the main device itself to prevent operator contact with live powered circuitry, to provide antistatic protection for components being added or removed, or to prevent the removable components from accidentally touching and shorting out the powered components in the operating device.

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.

Variations

There are two slightly differing meanings of the term hot swapping. It may refer only to the ability to add or remove hardware without powering down the system, while the system software may have to be notified by the user of the event in order to cope with it. Examples include RS-232 and lower-end SCSI devices.

Some implementations require a component shutdown 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, although this is not usually considered to be a problem.

More complex implementations may recommend but do not require that the component be shut down, with sufficient redundancy in the system to allow operation to continue if a component is removed without being shut down. In these systems hot swap is normally used for regular maintenance to the computer, or to replace a broken component.

Connectors

Sun SPARCstation hot swappable Single Connector Attachment (SCA) drive cradle SPARCstation20 scsi cradle with drive.jpg
Sun SPARCstation hot swappable Single Connector Attachment (SCA) drive cradle

Most modern hot-swap methods use a specialized connector with staggered pins, so that certain pins are certain to be connected before others. Most staggered-pin designs have ground pins longer than the others, ensuring that no sensitive circuitry is connected before there is a reliable system ground. The other pins may all be the same length, but in some cases three pin lengths are used so that the incoming device is grounded first, data lines connected second, and power applied third, in rapid succession as the device is inserted. Pins of the same nominal length do not necessarily make contact at exactly the same time due to mechanical tolerances, and angling of the connector when inserted.

At one time staggered pins were thought to be an expensive solution,[ citation needed ] 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.

Hot-swap connector corner pins Connector corners.svg
Hot-swap connector corner pins

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.

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. Real time 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. Real time 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).

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.

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.

Applications

Radio transmitters

Modern day radio transmitters (and some TV transmitters as well) use high power RF transistor power modules instead of vacuum tubes. Hot swapping power modules is not a new technology, as many of the radio transmitters manufactured in the 1930s were capable of having power tubes swapped out while the transmitter was running—but this feature was not universally adopted due to the introduction of more reliable high power tubes.

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:

Gaming

Although most contemporary video game systems can interchange games and multimedia (e.g. Blu-rays) without powering down the system, older generations of systems varied in their support of hot-swapping capabilities. For example, whereas the Sony PlayStation and PlayStation 2 could eject a game disc with the system powered on, the Nintendo Game Boy Advance and the Nintendo 64 would freeze up and could potentially become corrupt if the game cartridge was removed with the power on. Manufacturers specifically warned against such practices in the owner's manual or on the game cartridge. [4] It was supposedly for this reason that Stop 'N' Swop was taken out of the Banjo-Kazooie series. With the Sega Genesis/Mega Drive system, it was sometimes possible to apply cheats (such as a player having infinite lives) and other temporary software alterations to games by hot swapping cartridges, even though the cartridges were not designed to be hot swappable. [5]

Keyboards

Hot-swappable keyboards enable changing the switches without having to disassemble the keyboard. [6] On standard mechanical-switch keyboards, the switch is directly soldered to the PCB. Hot-swappable keyboards instead have a socket in its place that allows the switch to be freely replaced without re-soldering. [7]

Due to hot-swappable keyboards being less common, they often require being custom built or bought from custom keyboard manufacturers. [6] They can be found in a variety of sizes and layouts, including more specialized ergonomic layouts.

Software

Hot swapping can also refer to the ability to alter the running code of a program without needing to interrupt its execution. Interactive programming is a programming paradigm that makes extensive use of hot swapping, so the programming activity becomes part of the program flow itself.

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 [8] 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. [9]

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. [10]

Trademarks

The term "HOT PLUG" was registered as a trademark in the United States in November 1992 to Core International, Inc., and cancelled in May 1999. [11]

See also

Related Research Articles

<span class="mw-page-title-main">Backplane</span> Group of electrical connectors specifically aligned

A backplane or backplane system is a group of electrical connectors in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus. It is used to connect several printed circuit boards together to make up a complete computer system. Backplanes commonly use a printed circuit board, but wire-wrapped backplanes have also been used in minicomputers and high-reliability applications.

<span class="mw-page-title-main">Bus (computing)</span> System that transfers data between components within a computer

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.

<span class="mw-page-title-main">Motherboard</span> Main printed circuit board (PCB) used for a computing device

A motherboard is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals. Unlike a backplane, a motherboard usually contains significant sub-systems, such as the central processor, the chipset's input/output and memory controllers, interface connectors, and other components integrated for general use.

<span class="mw-page-title-main">Apple Desktop Bus</span> Proprietary bit-serial peripheral bus

Apple Desktop Bus (ADB) is a proprietary bit-serial peripheral bus connecting low-speed devices to computers. It was introduced on the Apple IIGS in 1986 as a way to support low-cost devices like keyboards and mice, enabling them to be connected together in a daisy chain without the need for hubs or other devices. Apple Desktop Bus was quickly introduced on later Macintosh models, on later models of NeXT computers, and saw some other third-party use as well. Like the similar PS/2 connector used in many PC-compatibles at the time, Apple Desktop Bus was rapidly replaced by USB as that system became popular in the late 1990s; the last external Apple Desktop Bus port on an Apple product was in 1999, though it remained as an internal-only bus on some Mac models into the 2000s.

<span class="mw-page-title-main">Electrical connector</span> Device used to join electrical conductors

Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between parts of an electrical circuit, or between different electrical circuits, thereby joining them into a larger circuit.

<span class="mw-page-title-main">SATA</span> Computer bus interface for storage devices

SATA is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard to become the predominant interface for storage devices.

<span class="mw-page-title-main">Serial communication</span> Type of data transfer

In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels.

<span class="mw-page-title-main">DIN connector</span> Electrical connector

The DIN connector is an electrical connector that was standardized by the Deutsches Institut für Normung (DIN), the German Institute for Standards, in the mid 1950's, initially with 3 pins for mono, but when stereo connections and gear appeared in late 1950's, versions with 5 pins or more were launched. The male DIN connectors (plugs) feature a 13.2 mm diameter metal shield with a notch that limits the orientation in which plug and socket can mate. The range of DIN connectors, different only in the configuration of the pins, have been standardized as DIN 41524 / IEC/DIN EN 60130-9 ; DIN 45322 ; DIN 45329 / IEC/DIN EN 60130–9 ; and DIN 45326 / IEC/DIN EN 60130-9.

<span class="mw-page-title-main">D-subminiature</span> Type of electrical connector

The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems.

<span class="mw-page-title-main">VGA connector</span> 15-pin video connector

The Video Graphics Array (VGA) connector is a standard connector used for computer video output. Originating with the 1987 IBM PS/2 and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, as well as many monitors, projectors and high-definition television sets.

<span class="mw-page-title-main">Disk enclosure</span> Specialized casing

A disk enclosure is a specialized casing designed to hold and power hard disk drives or solid state drives while providing a mechanism to allow them to communicate to one or more separate computers.

<span class="mw-page-title-main">Molex connector</span> Two-piece pin-and-socket connector

A Molex connector is a two-piece pin-and-socket interconnection which became an early electronic standard. Developed by Molex Connector Company in the late 1950s, the design features cylindrical spring-metal pins that fit into cylindrical spring-metal sockets, both held in a rectangular matrix in a nylon shell.

<span class="mw-page-title-main">Parallel Bus Interface</span>

The Parallel Bus Interface, or PBI, is a 50-pin port found on some XL models of the Atari 8-bit computers. It provides unbuffered, direct connection to the system bus lines, running at the same speed as the 6502 CPU. The 600XL and 800XL, along with the unreleased 1400XL and 1450XLD have a PBI interface.

<span class="mw-page-title-main">PS/2 port</span> 6-pin mini-DIN connector for connecting keyboards and mice to a PC compatible computer

The PS/2 port is a 6-pin mini-DIN connector used for connecting keyboards and mice to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mouse connector generally replaced the older DE-9 RS-232 "serial mouse" connector, while the PS/2 keyboard connector replaced the larger 5-pin/180° DIN connector used in the IBM PC/AT design. The PS/2 keyboard port is electrically and logically identical to the IBM AT keyboard port, differing only in the type of electrical connector used. The PS/2 platform introduced a second port with the same design as the keyboard port for use to connect a mouse; thus the PS/2-style keyboard and mouse interfaces are electrically similar and employ the same communication protocol. However, unlike the otherwise similar Apple Desktop Bus connector used by Apple, a given system's keyboard and mouse port may not be interchangeable since the two devices use different sets of commands and the device drivers generally are hard-coded to communicate with each device at the address of the port that is conventionally assigned to that device.

<span class="mw-page-title-main">Commodore 64 peripherals</span>

The Commodore 64 home computer used various external peripherals. Due to the backwards compatibility of the Commodore 128, most peripherals would also work on that system. There is also some compatibility with the VIC-20 and Commodore PET.

The Apple Network Server (ANS) was a line of PowerPC-based server computers designed, manufactured and sold by Apple Computer, Inc. from February 1996 to April 1997. It was codenamed "Shiner" and originally consisted of two models, the Network Server 500/132 and the Network Server 700/150, which got a companion model, the Network Server 700/200 with a faster CPU in November 1996.

A SCSI connector is used to connect computer parts that communicate with each other via the SCSI standard. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a computer and a disk drive, to communicate with each other. SCSI connectors can be electrical connectors or optical connectors. There have been a large variety of SCSI connectors in use at one time or another in the computer industry. Twenty-five years of evolution and three major revisions of the standards resulted in requirements for Parallel SCSI connectors that could handle an 8, 16 or 32 bit wide bus running at 5, 10 or 20 megatransfer/s, with conventional or differential signaling. Serial SCSI added another three transport types, each with one or more connector types. Manufacturers have frequently chosen connectors based on factors of size, cost, or convenience at the expense of compatibility.

<span class="mw-page-title-main">Parallel SCSI</span> Original SCSI storage interface

Parallel SCSI is the earliest of the interface implementations in the SCSI family. SPI is a parallel bus; there is one set of electrical connections stretching from one end of the SCSI bus to the other. A SCSI device attaches to the bus but does not interrupt it. Both ends of the bus must be terminated.

<span class="mw-page-title-main">Computer port (hardware)</span> Computer hardware

A computer port is a hardware piece on a computer where an electrical connector can be plugged to link the device to external devices, such as another computer, a peripheral device or network equipment.

<span class="mw-page-title-main">Modular crate electronics</span> Electronic used in particle generators

Modular crate electronics are a general type of electronics and support infrastructure commonly used for trigger electronics and data acquisition in particle detectors. These types of electronics are common in such detectors because all the electronic pathways are made by discrete physical cables connecting together logic blocks on the fronts of modules. This allows circuits to be designed, built, tested, and deployed very quickly as an experiment is being put together. Then the modules can all be removed and used again when the experiment is done.

References

  1. Hennessy, John L.; Patterson, David A. (2002). Computer Architecture: A Quantitative Approach. The Morgan Kaufmann Series in Computer Architecture and Design. Morgan Kaufmann. p. 707. ISBN   9780080502526.
  2. "Hot Swap and Hot Plug". Searchstorage.techtarget.com. TechTarget . Retrieved 2013-08-18.
  3. Tabisz, W.A.; Jovanovic, M.M.; Lee, F.C. (23–27 February 1992). Present and future of distributed power systems. Seventh Annual Applied Power Electronics Conference and Exposition, 1992. APEC '92. Conference Proceedings 1992. IEEE. pp. 11–12. doi:10.1109/APEC.1992.228437. ISBN   0-7803-0485-3. A properly designed parallel configuration allows the on-line replacement (hot-swapping) of defective modules. This provides means for non-interrupting maintenance and repair, a very desirable feature in high-reliability systems operating in a continuous fashion.
  4. "Health & Safety Precautions for Cartridge-Based Consoles". nintendo.com. Nintendo . Retrieved 2014-04-22.
  5. The editors of GamePro magazine (1994). Sega Genesis Games Secrets Greatest Tips (2nd ed.). Prima Publishing. p. 217. ISBN   9781559584012 . Retrieved 2014-05-12.{{cite book}}: |author= has generic name (help)
  6. 1 2 "What are hot-swappable keyboard switches?". Digital Trends. 2022-09-15. Retrieved 2022-12-02.
  7. "The 8 Best Hot Swappable Mechanical Keyboards – Review Geek". www.reviewgeek.com. 9 February 2020. Retrieved 2022-12-02.
  8. "Interactive programming – Hot-swapping in Elm". elm-lang.org. Archived from the original on 2013-10-06. Retrieved 2015-02-15.
  9. "MSDN Article for Edit and Continue". Msdn.microsoft.com. Archived from the original on 2010-07-31. Retrieved 2013-08-18.
  10. Gille, Christoph; Robinson, Peter N. (2006). "HotSwap for bioinformatics: A STRAP tutorial". BMC Bioinformatics. 7. Biomedcentral.com: 64. doi: 10.1186/1471-2105-7-64 . PMC   1386713 . PMID   16469097. S2CID   18283272.
  11. "Trademark Status & Document Retrieval (TSDR); Mark: HOT PLUG; US Serial Number: 74140414; Application Filing Date: Feb. 19, 1991; US Registration Number: 1732038; Registration Date: Nov. 10, 1992". USPTO. Retrieved 27 November 2016.