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[[File:Alps Electric DFR883F02A-2647.jpg|thumb|3.5" [[Floppy disk|Floppy disk drive]] by [[Alps Electric]] with FRU number]]
''This article is primarily about FRUs in computers.''
A '''field -replaceable unit''' ( '''FRU ''')<ref name= "Newton16p364 " /> is a [[ printed circuit board]], part , or assembly that can be quickly and easily removed from a [[ personal computer]] or other piece of [[electronic equipment ]], and replaced by the user or a technician without having to send the entire product or system to a repair facility. FRUs allow a technician lacking in-depth product knowledge to [[fault detection and isolation| fault isolate faults]] and replace faulty components . The granularity of FRUs in a system impacts [[total cost of ownership]] and support, including the costs of stocking [[spare part]]s, where spares are deployed to meet repair time goals, how diagnostic tools are designed and implemented, levels of training for field personnel, whether end-users can do their own FRU replacement, etc. ▼
▲A '''field replaceable unit''' ('FRU)<ref name="Newton16p364" /> is a [[circuit board]], part or assembly that can be quickly and easily removed from a [[personal computer]] or other piece of [[electronic equipment]], and replaced by the user or a technician without having to send the entire product or system to a repair facility. FRUs allow a technician lacking in-depth product knowledge to [[fault detection and isolation|fault isolate]] and replace faulty components.
==Computer hardware==
A typical [[desktop computer]] is composed almost entirely of FRUs, including:
* [[Power supply unit]]s
* [[Motherboard]]s
* socketed [[CPU|microprocessors]]
* [[Computer data storage#Primary storage|primary storage modules]]
** [[RAM]]
* [[Computer data storage#Secondary storage|secondary storage devices]]
** [[hard drive]]s
** [[optical drive]]s
** [[floppy drive]]s
* [[Computer bus|Bus]] devices
** [[video card]]s
** [[sound card]]s
* Cooling fans
* [[Peripheral]]s
** [[computer keyboard|keyboards]]
** [[mouse (computing)|mice]]
** [[Computer printer|printers]]
** [[cable|connecting cables]]s
Replacing an FRU while the machine is running is known as [[hot swapping]]. Support for hot swapping is mostly limited to [[high availability]] devices, power supplies, and cooling fans in systems having redundant ones.
To aid in fault isolation, a unit called a field replaceable unit identifier (FRU ID) holds the records of the devices that do not originally come with the baseboard or motherboard. Most (though not all) board manufacturers use EEPROM to store FRU IDs, which play a significant role in [[Intelligent Platform Management Interface|IPMI]]. The [[Baseboard management controller|BMC]] contacts the FRU devices whenever there is a problem in the hardware to determine the device to replace. Most often, the BMC communicates with the FRU using the [[I²C]] bus protocol, but can also use other implementation-specific protocols.
==Other equipment==
FRUs are not strictly confined to computers but are also part of many high-end, lower -volume consumer and commercial products. For example, in military aviation, electronic components of [[line-replaceable unit]]s, typically known as [[shop-replaceable unitsunit]]s (SRUs), are repaired at field-service [[Workshop#Backshop|backshop]]s, usually by a "remove and replace" repair procedure, with specialized repair performed at centralized depot or by the [[Originaloriginal equipment manufacturer|OEM]].
==History==
Many [[vacuum tube]] computers had FRUs:
*[[ Pluggable unit]]sunits containing one or more [[vacuum tube]]s and various [[passive component]]s
Most [[transistor]]ized and [[integrated circuit]]-based computers had FRUs:
*Circuit [[Computer module]]s, circuit boards containing discrete transistors and various passive components. Some examplesExamples:
** [[IBM Standard Modular System|IBM SMS cards]]
** [[System Building Blocks|DEC System Building Blocks]] cards
** [[Flip -Chip (trademark)module|DEC Flip-Chip]] cards
* Circuit boards containing monolithic ICs and/or [[hybrid integrated circuit|hybrid ICs]], such as [[Solid Logic Technology|IBM SLT cards]].
Vacuum tubes themselves are usually FRUs.
For a short period starting in the late 1960s, some [[television set]] manufacturers started makingmade solid-state televisions with FRUs instead of a single board attached to the chassis. However all modern televisions put all the electronics on one large board to reduce manufacturing costs.
==Trends==
As the sophistication and complexity of multi-replaceable unit electronics in both commercial and consumer industries have increased, many design and manufacturing organizations have expanded the use of the FRU storage device.{{definition needed|date=August 2019}} Storage is no longer limited to simply identification of the FRU itself, but now also comprises back-up copies of critical system information such as system serial numbers, MAC address and even security information. Some systems will fail to function at all without each FRU in the system being ratified at start-up. Today one cannot assume that the FRU storage device is only used to maintain the FRU ID of the part.
==See also==
* [[Shop-replaceable unit]]
* [[Line-replaceable unit]]
==Notes==
{{Reflist|refs=
<ref name="Newton16p364">Newton, Harry: ''Newton's Telecom Dictionary'', 16th Edition, "FRU," p. 364.</ref>
}}
[[Category:Electronic engineering]] ▼[[Category:Maintenance]]
▲[[Category:Electronic engineering]]
[[de:Field Replaceable Unit]]
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