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PCI Express
PCI Express
(Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e,[1] is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X, and AGP bus standards. PCIe has numerous improvements over the older standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting, AER[2]), and native hot-swap functionality. More recent revisions of the PCIe standard provide hardware support for I/O virtualization. The PCI Express
PCI Express
electrical interface is also used in a variety of other standards, most notably the laptop expansion card interface ExpressCard
ExpressCard
and computer storage interfaces SATA Express
SATA Express
and M.2. Format specifications are maintained and developed by the PCI-SIG (PCI Special
Special
Interest Group), a group of more than 900 companies that also maintain the conventional PCI specifications. PCIe 3.0 is the latest standard for expansion cards that are in production and available on mainstream personal computers.[3][4]

Contents

1 Architecture

1.1 Interconnect 1.2 Lane 1.3 Serial bus

2 Form factors

2.1 PCI Express
PCI Express
(standard)

2.1.1 Pinout 2.1.2 Power

2.2 PCI Express
PCI Express
Mini Card

2.2.1 Physical dimensions 2.2.2 Electrical interface 2.2.3 Mini-SATA (mSATA) variant 2.2.4 Mini PCIe v2

2.3 PCI Express
PCI Express
External Cabling 2.4 Derivative forms

3 History and revisions

3.1 PCI Express
PCI Express
1.0a 3.2 PCI Express
PCI Express
1.1 3.3 PCI Express
PCI Express
2.0 3.4 PCI Express
PCI Express
2.1 3.5 PCI Express
PCI Express
3.0 3.6 PCI Express
PCI Express
3.1 3.7 PCI Express
PCI Express
4.0 3.8 PCI Express
PCI Express
5.0 3.9 Extensions and future directions

4 Hardware protocol summary

4.1 Physical layer

4.1.1 Data transmission

4.2 Data link layer 4.3 Transaction layer

5 Applications

5.1 External GPUs 5.2 Storage devices 5.3 Cluster interconnect

6 Competing protocols 7 See also 8 Notes 9 References 10 Further reading 11 External links

Architecture[edit]

An example of the PCI Express topology; white "junction boxes" represent PCI Express device downstream ports, while the gray ones represent upstream ports.[5]:7

A PCI Express
PCI Express
×1 card containing a PCI Express
PCI Express
switch (covered by a small heat sink), which creates multiple endpoints out of one endpoint and allows it to be shared by multiple devices

Conceptually, the PCI Express
PCI Express
bus is a high-speed serial replacement of the older PCI/ PCI-X
PCI-X
bus.[6] One of the key differences between the PCI Express
PCI Express
bus and the older PCI is the bus topology; PCI uses a shared parallel bus architecture, in which the PCI host and all devices share a common set of address, data and control lines. In contrast, PCI Express
PCI Express
is based on point-to-point topology, with separate serial links connecting every device to the root complex (host). Due to its shared bus topology, access to the older PCI bus is arbitrated (in the case of multiple masters), and limited to one master at a time, in a single direction. Furthermore, the older PCI clocking scheme limits the bus clock to the slowest peripheral on the bus (regardless of the devices involved in the bus transaction). In contrast, a PCI Express
PCI Express
bus link supports full-duplex communication between any two endpoints, with no inherent limitation on concurrent access across multiple endpoints. In terms of bus protocol, PCI Express
PCI Express
communication is encapsulated in packets. The work of packetizing and de-packetizing data and status-message traffic is handled by the transaction layer of the PCI Express port (described later). Radical differences in electrical signaling and bus protocol require the use of a different mechanical form factor and expansion connectors (and thus, new motherboards and new adapter boards); PCI slots and PCI Express
PCI Express
slots are not interchangeable. At the software level, PCI Express
PCI Express
preserves backward compatibility with PCI; legacy PCI system software can detect and configure newer PCI Express
PCI Express
devices without explicit support for the PCI Express
PCI Express
standard, though new PCI Express
PCI Express
features are inaccessible. The PCI Express
PCI Express
link between two devices can consist of anywhere from one to 32 lanes. In a multi-lane link, the packet data is striped across lanes, and peak data throughput scales with the overall link width. The lane count is automatically negotiated during device initialization, and can be restricted by either endpoint. For example, a single-lane PCI Express
PCI Express
(×1) card can be inserted into a multi-lane slot (×4, ×8, etc.), and the initialization cycle auto-negotiates the highest mutually supported lane count. The link can dynamically down-configure itself to use fewer lanes, providing a failure tolerance in case bad or unreliable lanes are present. The PCI Express standard defines slots and connectors for multiple widths: ×1, ×4, ×8, ×12, ×16 and ×32.[5]:4,5 This allows the PCI Express
PCI Express
bus to serve both cost-sensitive applications where high throughput is not needed, as well as performance-critical applications such as 3D graphics, networking ( 10 Gigabit Ethernet
10 Gigabit Ethernet
or multiport Gigabit Ethernet), and enterprise storage (SAS or Fibre Channel). As a point of reference, a PCI-X
PCI-X
(133 MHz 64-bit) device and a PCI Express 1.0 device using four lanes (×4) have roughly the same peak single-direction transfer rate of 1064 MB/s. The PCI Express bus has the potential to perform better than the PCI-X
PCI-X
bus in cases where multiple devices are transferring data simultaneously, or if communication with the PCI Express
PCI Express
peripheral is bidirectional. Interconnect[edit]

A PCI Express
PCI Express
link between two devices consists of one or more lanes, which are dual simplex channels using two differential signaling pairs.[5]:3

PCI Express
PCI Express
devices communicate via a logical connection called an interconnect[7] or link. A link is a point-to-point communication channel between two PCI Express
PCI Express
ports allowing both of them to send and receive ordinary PCI requests (configuration, I/O or memory read/write) and interrupts (INTx, MSI or MSI-X). At the physical level, a link is composed of one or more lanes.[7] Low-speed peripherals (such as an 802.11 Wi-Fi
Wi-Fi
card) use a single-lane (×1) link, while a graphics adapter typically uses a much wider and faster 16-lane link. Lane[edit] A lane is composed of two differential signaling pairs, with one pair for receiving data and the other for transmitting. Thus, each lane is composed of four wires or signal traces. Conceptually, each lane is used as a full-duplex byte stream, transporting data packets in eight-bit "byte" format simultaneously in both directions between endpoints of a link.[8] Physical PCI Express
PCI Express
links may contain from one to 32 lanes, more precisely 1, 2, 4, 8, 12, 16 or 32 lanes.[5]:4,5[7] Lane counts are written with an "×" prefix (for example, "×8" represents an eight-lane card or slot), with ×16 being the largest size in common use.[9] For mechanical card sizes, see below. Serial bus[edit]

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The bonded serial bus architecture was chosen over the traditional parallel bus due to inherent limitations of the latter, including half-duplex operation, excess signal count, and inherently lower bandwidth due to timing skew. Timing skew
Timing skew
results from separate electrical signals within a parallel interface traveling through conductors of different lengths, on potentially different printed circuit board (PCB) layers, and at possibly different signal velocities. Despite being transmitted simultaneously as a single word, signals on a parallel interface have different travel duration and arrive at their destinations at different times. When the interface clock period is shorter than the largest time difference between signal arrivals, recovery of the transmitted word is no longer possible. Since timing skew over a parallel bus can amount to a few nanoseconds, the resulting bandwidth limitation is in the range of hundreds of megahertz. A serial interface does not exhibit timing skew because there is only one differential signal in each direction within each lane, and there is no external clock signal since clocking information is embedded within the serial signal itself. As such, typical bandwidth limitations on serial signals are in the multi-gigahertz range. PCI Express is one example of the general trend toward replacing parallel buses with serial interconnects; other examples include Serial ATA (SATA), USB, Serial Attached SCSI
Serial Attached SCSI
(SAS), FireWire
FireWire
(IEEE 1394), and RapidIO. In digital video, examples in common use are DVI, HDMI
HDMI
and DisplayPort. Multichannel serial design increases flexibility with its ability to allocate fewer lanes for slower devices. Form factors[edit] PCI Express
PCI Express
(standard)[edit]

Various slots on a computer motherboard, from top to bottom:

PCI Express
PCI Express
×4 PCI Express
PCI Express
×16 PCI Express
PCI Express
×1 PCI Express
PCI Express
×16 Conventional PCI
Conventional PCI
(32-bit, 5 V)

An open-ended PCI express ×1 slot

A PCI Express
PCI Express
card fits into a slot of its physical size or larger (with ×16 as the largest used), but may not fit into a smaller PCI Express slot; for example, a ×16 card may not fit into a ×4 or ×8 slot. Some slots use open-ended sockets to permit physically longer cards and negotiate the best available electrical and logical connection. The number of lanes actually connected to a slot may also be fewer than the number supported by the physical slot size. An example is a ×16 slot that runs at ×4, which will accept any ×1, ×2, ×4, ×8 or ×16 card, but provides only four lanes. Its specification may read as "×16 (×4 mode)", while "×size @ ×speed" notation ("×16 @ ×4") is also common. The advantage is that such slots can accommodate a larger range of PCI Express
PCI Express
cards without requiring motherboard hardware to support the full transfer rate. Standard mechanical sizes are ×1, ×4, ×8, and ×16. Cards with a differing number of lanes need to use the next larger mechanical size (ie. a ×2 card uses the ×4 size, or a ×12 card uses the ×16 size). The cards themselves are designed and manufactured in various sizes. For example, solid-state drives (SSDs) that come in the form of PCI Express cards often use HHHL (half height, half length) and FHHL (full height, half length) to describe the physical dimensions of the card.[10][11] Pinout[edit] The following table identifies the conductors on each side of the edge connector on a PCI Express
PCI Express
card. The solder side of the printed circuit board (PCB) is the A side, and the component side is the B side.[12] PRSNT1# and PRSNT2# pins must be slightly shorter than the rest, to ensure that a hot-plugged card is fully inserted. The WAKE# pin uses full voltage to wake the computer, but must be pulled high from the standby power to indicate that the card is wake capable.[13]

PCI Express
PCI Express
connector pinout (×1, ×4, ×8 and ×16 variants)

Pin Side B Side A Description

Pin Side B Side A Description

1 +12 V PRSNT1# Must connect to farthest PRSNT2# pin 50 HSOp(8) Reserved Lane 8 transmit data, + and −

2 +12 V +12 V Main power pins 51 HSOn(8) Ground

3 +12 V +12 V 52 Ground HSIp(8) Lane 8 receive data, + and −

4 Ground Ground

53 Ground HSIn(8)

5 SMCLK TCK SMBus and JTAG
JTAG
port pins 54 HSOp(9) Ground Lane 9 transmit data, + and −

6 SMDAT TDI 55 HSOn(9) Ground

7 Ground TDO 56 Ground HSIp(9) Lane 9 receive data, + and −

8 +3.3 V TMS 57 Ground HSIn(9)

9 TRST# +3.3 V 58 HSOp(10) Ground Lane 10 transmit data, + and −

10 +3.3 V aux +3.3 V Standby power 59 HSOn(10) Ground

11 WAKE# PERST# Link reactivation; fundamental reset 60 Ground HSIp(10) Lane 10 receive data, + and −

Key notch 61 Ground HSIn(10)

12 CLKREQ# Ground Request running clock 62 HSOp(11) Ground Lane 11 transmit data, + and −

13 Ground REFCLK+ Reference clock differential pair 63 HSOn(11) Ground

14 HSOp(0) REFCLK− Lane 0 transmit data, + and − 64 Ground HSIp(11) Lane 11 receive data, + and −

15 HSOn(0) Ground 65 Ground HSIn(11)

16 Ground HSIp(0) Lane 0 receive data, + and − 66 HSOp(12) Ground Lane 12 transmit data, + and −

17 PRSNT2# HSIn(0) 67 HSOn(12) Ground

18 Ground Ground

68 Ground HSIp(12) Lane 12 receive data, + and −

PCI Express
PCI Express
×1 cards end at pin 18 69 Ground HSIn(12)

19 HSOp(1) Reserved Lane 1 transmit data, + and − 70 HSOp(13) Ground Lane 13 transmit data, + and −

20 HSOn(1) Ground 71 HSOn(13) Ground

21 Ground HSIp(1) Lane 1 receive data, + and − 72 Ground HSIp(13) Lane 13 receive data, + and −

22 Ground HSIn(1) 73 Ground HSIn(13)

23 HSOp(2) Ground Lane 2 transmit data, + and − 74 HSOp(14) Ground Lane 14 transmit data, + and −

24 HSOn(2) Ground 75 HSOn(14) Ground

25 Ground HSIp(2) Lane 2 receive data, + and − 76 Ground HSIp(14) Lane 14 receive data, + and −

26 Ground HSIn(2) 77 Ground HSIn(14)

27 HSOp(3) Ground Lane 3 transmit data, + and − 78 HSOp(15) Ground Lane 15 transmit data, + and −

28 HSOn(3) Ground 79 HSOn(15) Ground

29 Ground HSIp(3) Lane 3 receive data, + and − 80 Ground HSIp(15) Lane 15 receive data, + and −

30 Reserved HSIn(3) 81 PRSNT2# HSIn(15)

31 PRSNT2# Ground

82 Reserved Ground

32 Ground Reserved

PCI Express
PCI Express
×4 cards end at pin 32

33 HSOp(4) Reserved Lane 4 transmit data, + and −

34 HSOn(4) Ground

35 Ground HSIp(4) Lane 4 receive data, + and −

36 Ground HSIn(4)

37 HSOp(5) Ground Lane 5 transmit data, + and −

38 HSOn(5) Ground

39 Ground HSIp(5) Lane 5 receive data, + and −

40 Ground HSIn(5)

41 HSOp(6) Ground Lane 6 transmit data, + and −

42 HSOn(6) Ground

43 Ground HSIp(6) Lane 6 receive data, + and − Legend

44 Ground HSIn(6) Ground pin Zero volt reference

45 HSOp(7) Ground Lane 7 transmit data, + and − Power pin Supplies power to the PCIe card

46 HSOn(7) Ground Card-to-host pin Signal from the card to the motherboard

47 Ground HSIp(7) Lane 7 receive data, + and − Host-to-card pin Signal from the motherboard to the card

48 PRSNT2# HSIn(7) Open drain May be pulled low or sensed by multiple cards

49 Ground Ground

Sense pin Tied together on card

PCI Express
PCI Express
×8 cards end at pin 49 Reserved Not presently used, do not connect

Power[edit]

8-pin (left) and 6-pin (right) power connectors used on PCI Express cards

All PCI express cards may consume up to 7000300000000000000♠3 A at 7000330000000000000♠+3.3 V (7000990000000000000♠9.9 W). The amount of +12 V and total power they may consume depends on the type of card:[14]:35–36[15]

×1 cards are limited to 0.5 A at +12V (6 W) and 10 W combined. ×4 and wider cards are limited to 2.1 A at +12V (25 W) and 25 W combined. A full-sized ×1 card may draw up to the 25 W limits after initialization and software configuration as a "high power device". A full-sized ×16 graphics card[13] may draw up to 5.5 A at +12V (66 W) and 75 W combined after initialization and software configuration as a "high power device". Sense0 pin is connected to ground by the cable or power supply, or float on board if cable is not connected. Sense1 pin is connected to +12V by the cable or power supply, or float on board if cable is not connected.

Optional connectors add 75 W (6-pin) or 150 W (8-pin) of +12 V power for up to 300 W total (2×75 W + 1×150 W). Some cards are using two 8-pin connectors, but this has not been standardized yet, therefore such cards must not carry the official PCI Express
PCI Express
logo. This configuration allows 375 W total (1×75 W + 2×150 W) and will likely be standardized by PCI-SIG with the PCI Express
PCI Express
4.0 standard. The 8-pin PCI Express connector could be confused with the EPS12V
EPS12V
connector, which is mainly used for powering SMP and multi-core systems.

6-pin power connector (75 W)[16]

8-pin power connector (150 W)[17][18][19]

6 pin power connector pin map

8 pin power connector pin map

Pin Description Pin Description

1 +12 V 1 +12 V

2 Not connected (usually +12 V as well) 2 +12 V

3 +12 V 3 +12 V

4 Sense1 (8-pin connected[a])

4 Ground 5 Ground

5 Sense 6 Sense0 (6-pin or 8-pin connected)

6 Ground 7 Ground

8 Ground

^ When a 6-pin connector is plugged into an 8-pin receptacle the card is notified by a missing Sense1 that it may only use up to 75 W.

PCI Express
PCI Express
Mini Card[edit]

A WLAN PCI Express
PCI Express
Mini Card and its connector

MiniPCI and Mini PCI Express
PCI Express
cards in comparison

PCI Express
PCI Express
Mini Card (also known as Mini PCI
Mini PCI
Express, Mini PCIe, Mini PCI-E, mPCIe, and PEM), based on PCI Express, is a replacement for the Mini PCI
Mini PCI
form factor. It is developed by the PCI-SIG. The host device supports both PCI Express
PCI Express
and USB 2.0 connectivity, and each card may use either standard. Most laptop computers built after 2005 use PCI Express
PCI Express
for expansion cards; however, as of 2015[update], many vendors are moving toward using the newer M.2
M.2
form factor for this purpose. Due to different dimensions, PCI Express
PCI Express
Mini Cards are not physically compatible with standard full-size PCI Express
PCI Express
slots; however, passive adapters exist that allow them to be used in full-size slots.[20] Physical dimensions[edit] Dimensions of PCI Express
PCI Express
Mini Cards are 30 × 50.95 mm (width × length) for a Full Mini Card. There is a 52-pin edge connector, consisting of two staggered rows on a 0.8 mm pitch. Each row has eight contacts, a gap equivalent to four contacts, then a further 18 contacts. Boards have a thickness of 1.0 mm, excluding the components. A "Half Mini Card" (sometimes abbreviated as HMC) is also specified, having approximately half the physical length of 26.8 mm. Electrical interface[edit] PCI Express
PCI Express
Mini Card edge connectors provide multiple connections and buses:

PCI Express
PCI Express
×1 (with SMBus) USB 2.0 Wires to diagnostics LEDs for wireless network (i.e., Wi-Fi) status on computer's chassis SIM card for GSM
GSM
and WCDMA
WCDMA
applications (UIM signals on spec.). Future extension for another PCIe lane 1.5 V and 3.3 V power

Mini-SATA (mSATA) variant[edit] Despite sharing the Mini PCI
Mini PCI
Express form factor, an mSATA slot is not necessarily electrically compatible with Mini PCI
Mini PCI
Express. For this reason, only certain notebooks are compatible with mSATA drives. Most compatible systems are based on Intel's Sandy Bridge processor architecture, using the Huron River platform. Notebooks like Lenovo's ThinkPad T, W and X series, released in March–April 2011, have support for an mSATA SSD card in their WWAN card slot. The ThinkPad Edge E220s/E420s, and the Lenovo IdeaPad Y460/Y560/Y570/Y580 also support mSATA.[21] Some notebooks (notably the Asus
Asus
Eee PC, the Apple MacBook Air, and the Dell
Dell
mini9 and mini10) use a variant of the PCI Express
PCI Express
Mini Card as an SSD. This variant uses the reserved and several non-reserved pins to implement SATA and IDE interface passthrough, keeping only USB, ground lines, and sometimes the core PCIe ×1 bus intact.[22] This makes the "miniPCIe" flash and solid-state drives sold for netbooks largely incompatible with true PCI Express
PCI Express
Mini implementations. Also, the typical Asus
Asus
miniPCIe SSD is 71 mm long, causing the Dell
Dell
51 mm model to often be (incorrectly) referred to as half length. A true 51 mm Mini PCIe SSD was announced in 2009, with two stacked PCB layers that allow for higher storage capacity. The announced design preserves the PCIe interface, making it compatible with the standard mini PCIe slot. No working product has yet been developed. Intel
Intel
has numerous desktop boards with the PCIe ×1 Mini-Card slot which typically do not support mSATA SSD. A list of desktop boards that natively support mSATA in the PCIe ×1 Mini-Card slot (typically multiplexed with a SATA port) is provided on the Intel
Intel
Support site.[23] Mini PCIe v2[edit] Main article: M.2 The new version of Mini PCI
Mini PCI
express, M.2
M.2
replaces the mSATA standard. Computer
Computer
bus interfaces provided through the M.2
M.2
connector are PCI Express 3.0 (up to four lanes), Serial ATA
Serial ATA
3.0, and USB
USB
3.0 (a single logical port for each of the latter two). It is up to the manufacturer of the M.2
M.2
host or device to select which interfaces are to be supported, depending on the desired level of host support and device type. PCI Express
PCI Express
External Cabling[edit] PCI Express
PCI Express
External Cabling (also known as External PCI Express, Cabled PCI Express, or ePCIe) specifications were released by the PCI-SIG in February 2007.[24][25] Standard cables and connectors have been defined for ×1, ×4, ×8, and ×16 link widths, with a transfer rate of 250 MB/s per lane. The PCI-SIG also expects the norm will evolve to reach 500 MB/s, as in PCI Express
PCI Express
2.0. An example of the uses of Cabled PCI Express
PCI Express
is a metal enclosure, containing a number of PCI slots and PCI-to-ePCIe adapter circuitry. This device would not be possible had it not been for the ePCIe spec. Derivative forms[edit] Several other types of expansion card are derived from PCIe; these include:

Low-height card ExpressCard: Successor to the PC Card
PC Card
form factor (with ×1 PCIe and USB
USB
2.0; hot-pluggable) PCI Express
PCI Express
ExpressModule: A hot-pluggable modular form factor defined for servers and workstations XQD card: A PCI Express-based flash card standard by the CompactFlash Association XMC: Similar to the CMC/PMC form factor (VITA 42.3) AdvancedTCA: A complement to CompactPCI
CompactPCI
for larger applications; supports serial based backplane topologies AMC: A complement to the AdvancedTCA specification; supports processor and I/O modules on ATCA boards (×1, ×2, ×4 or ×8 PCIe). FeaturePak: A tiny expansion card format (43 × 65 mm) for embedded and small-form-factor applications which implements two ×1 PCIe links on a high-density connector along with USB, I2C, and up to 100 points of I/O Universal IO: A variant from Super Micro Computer
Computer
Inc designed for use in low-profile rack-mounted chassis.[26] It has the connector bracket reversed so it cannot fit in a normal PCI Express
PCI Express
socket, but it is pin-compatible and may be inserted if the bracket is removed. Thunderbolt: A variant from Intel
Intel
that combines DisplayPort
DisplayPort
and PCIe protocols in a form factor compatible with Mini DisplayPort. Thunderbolt 3.0 also combines USB
USB
3.1 and uses the USB-C
USB-C
form factor as opposed to Mini DisplayPort. Serial Digital Video Out: Some 9xx series Intel
Intel
chipsets allow for adding another output for the integrated video into a PCIe slot (mostly dedicated and 16 lanes). M.2
M.2
(formerly known as NGFF) M-PCIe
M-PCIe
brings PCIe 3.0 to mobile devices (such as tablets and smartphones), over the M-PHY
M-PHY
physical layer.[27][28] U.2 (formerly known as SFF-8639)

History and revisions[edit] While in early development, PCIe was initially referred to as HSI (for High Speed Interconnect), and underwent a name change to 3GIO (for 3rd Generation I/O) before finally settling on its PCI-SIG name PCI Express. A technical working group named the Arapaho Work Group (AWG) drew up the standard. For initial drafts, the AWG consisted only of Intel
Intel
engineers; subsequently the AWG expanded to include industry partners. PCI Express
PCI Express
is a technology under constant development and improvement. As of 2013[update], PCI Express
PCI Express
version 4 has been drafted with final specifications expected in 2017.[29] At the 2016 PCI SIG’s annual developer’s conference and at the Intel
Intel
Developer Forum, Synopsys showed a system running on PCIe 4.0, while Mellanox
Mellanox
provided an appropriate network card.[30][31]

PCI Express
PCI Express
link performance[29][32]

PCI Express version Introduced Line code Transfer rate[i] Throughput[i]

×1 ×2 ×4 ×8 ×16

1.0 2003 8b/10b 2.5 GT/s 250 MB/s 0.50 GB/s 1.0 GB/s 2.0 GB/s 4.0 GB/s

2.0 2007 8b/10b 5.0 GT/s 500 MB/s 1.0 GB/s 2.0 GB/s 4.0 GB/s 8.0 GB/s

3.0 2010 128b/130b 8.0 GT/s 984.6 MB/s 1.97 GB/s 3.94 GB/s 7.88 GB/s 15.8 GB/s

4.0 2017 128b/130b 16.0 GT/s 1969 MB/s 3.94 GB/s 7.88 GB/s 15.75 GB/s 31.5 GB/s

5.0[30][31] expected in Q2 2019[33] 128b/130b 32.0 GT/s[ii] 3938 MB/s 7.88 GB/s 15.75 GB/s 31.51 GB/s 63.0 GB/s

^ a b In each direction (each lane is a dual simplex channel). ^ Initially, 25.0 GT/s were also considered for technical feasibility.

PCI Express
PCI Express
1.0a[edit] In 2003, PCI-SIG introduced PCIe 1.0a, with a per-lane data rate of 250 MB/s and a transfer rate of 2.5 gigatransfers per second (GT/s). Transfer rate is expressed in transfers per second instead of bits per second because the number of transfers includes the overhead bits, which do not provide additional throughput;[34] PCIe 1.x uses an 8b/10b
8b/10b
encoding scheme, resulting in a 20% (= 2/10) overhead on the raw channel bandwidth.[35] PCI Express
PCI Express
1.1[edit] In 2005, PCI-SIG[36] introduced PCIe 1.1. This updated specification includes clarifications and several improvements, but is fully compatible with PCI Express
PCI Express
1.0a. No changes were made to the data rate. PCI Express
PCI Express
2.0[edit]

A PCI Express 2.0 expansion card that provides USB 3.0 connectivity.[a]

PCI-SIG announced the availability of the PCI Express
PCI Express
Base 2.0 specification on 15 January 2007.[37] The PCIe 2.0 standard doubles the transfer rate compared with PCIe 1.0 to 5 GT/s and the per-lane throughput rises from 250 MB/s to 500 MB/s. Consequently, a 32-lane PCIe connector (×32) can support an aggregate throughput of up to 16 GB/s. PCIe 2.0 motherboard slots are fully backward compatible with PCIe v1.x cards. PCIe 2.0 cards are also generally backward compatible with PCIe 1.x motherboards, using the available bandwidth of PCI Express 1.1. Overall, graphic cards or motherboards designed for v2.0 will work with the other being v1.1 or v1.0a. The PCI-SIG also said that PCIe 2.0 features improvements to the point-to-point data transfer protocol and its software architecture.[38] Intel's first PCIe 2.0 capable chipset was the X38 and boards began to ship from various vendors (Abit, Asus, Gigabyte) as of October 21, 2007.[39] AMD started supporting PCIe 2.0 with its AMD 700 chipset series and nVidia started with the MCP72.[40] All of Intel's prior chipsets, including the Intel
Intel
P35 chipset, supported PCIe 1.1 or 1.0a.[41] Like 1.x, PCIe 2.0 uses an 8b/10b
8b/10b
encoding scheme, therefore delivering, per-lane, an effective 4 Gbit/s max transfer rate from its 5 GT/s raw data rate. PCI Express
PCI Express
2.1[edit] PCI Express
PCI Express
2.1 (with its specification dated March 4, 2009) supports a large proportion of the management, support, and troubleshooting systems planned for full implementation in PCI Express
PCI Express
3.0. However, the speed is the same as PCI Express
PCI Express
2.0. The increase in power from the slot breaks backward compatibility between PCI Express
PCI Express
2.1 cards and some older motherboards with 1.0/1.0a, but most motherboards with PCI Express
PCI Express
1.1 connectors are provided with a BIOS
BIOS
update by their manufacturers through utilities to support backward compatibility of cards with PCIe 2.1. PCI Express
PCI Express
3.0[edit] PCI Express
PCI Express
3.0 Base specification revision 3.0 was made available in November 2010, after multiple delays. In August 2007, PCI-SIG announced that PCI Express
PCI Express
3.0 would carry a bit rate of 8 gigatransfers per second (GT/s), and that it would be backward compatible with existing PCI Express
PCI Express
implementations. At that time, it was also announced that the final specification for PCI Express
PCI Express
3.0 would be delayed until Q2 2010.[42] New features for the PCI Express 3.0 specification include a number of optimizations for enhanced signaling and data integrity, including transmitter and receiver equalization, PLL improvements, clock data recovery, and channel enhancements for currently supported topologies.[43] Following a six-month technical analysis of the feasibility of scaling the PCI Express
PCI Express
interconnect bandwidth, PCI-SIG's analysis found that 8 gigatransfers per second can be manufactured in mainstream silicon process technology, and can be deployed with existing low-cost materials and infrastructure, while maintaining full compatibility (with negligible impact) to the PCI Express
PCI Express
protocol stack. PCI Express 3.0 upgrades the encoding scheme to 128b/130b
128b/130b
from the previous 8b/10b
8b/10b
encoding, reducing the bandwidth overhead from 20% of PCI Express 2.0 to approximately 1.54% (= 2/130). This is achieved by XORing a known binary polynomial as a "scrambler" to the data stream in a feedback topology. Because the scrambling polynomial is known, the data can be recovered by running applying the XOR
XOR
a second time. PCI Express
PCI Express
3.0's 8 GT/s bit rate effectively delivers 985 MB/s per lane, nearly doubling the lane bandwidth relative to PCI Express
PCI Express
2.0.[32] On November 18, 2010, the PCI Special Interest Group officially published the finalized PCI Express
PCI Express
3.0 specification to its members to build devices based on this new version of PCI Express.[44] PCI Express
PCI Express
3.1[edit] In September 2013, PCI Express 3.1 specification was announced to be released in late 2013 or early 2014, consolidating various improvements to the published PCI Express 3.0 specification in three areas: power management, performance and functionality.[28][45] It was released in November 2014.[46] PCI Express
PCI Express
4.0[edit] On November 29, 2011, PCI-SIG preliminarily announced PCI Express 4.0,[47] providing a 16 GT/s bit rate that doubles the bandwidth provided by PCI Express
PCI Express
3.0, while maintaining backward and forward compatibility in both software support and used mechanical interface.[48] PCI Express
PCI Express
4.0 specs will also bring OCuLink-2, an alternative to Thunderbolt connector. OCuLink version 2 will have up to 16 GT/s (8 GB/s total for ×4 lanes),[49] while the maximum bandwidth of a Thunderbolt 3 connector is 5 GB/s. Additionally, active and idle power optimizations are to be investigated. In August 2016, Synopsys
Synopsys
presented a test machine running PCIe 4.0 at the Intel
Intel
Developer Forum. Their IP has been licensed to several firms planning to present their chips and products at the end of 2016.[31] PCI Express
PCI Express
4.0 was officially announced on June 8, 2017, by PCI-SIG.[50] The spec includes improvements in flexibility, scalability, and lower-power. PCI Express
PCI Express
5.0[edit] In June 2017, PCI-SIG preliminarily announced the PCI Express
PCI Express
5.0 specification.[50] Bandwidth is expected to increase to 32 GT/s, yielding 128 GB/s in full duplex networking configurations. It is expected to be standardized in 2019. Extensions and future directions[edit] Some vendors offer PCIe over fiber products,[51][52][53] but these generally find use only in specific cases where transparent PCIe bridging is preferable to using a more mainstream standard (such as InfiniBand
InfiniBand
or Ethernet) that may require additional software to support it; current implementations focus on distance rather than raw bandwidth and typically do not implement a full ×16 link. Thunderbolt was co-developed by Intel
Intel
and Apple as a general-purpose high speed interface combining a ×4 PCIe link with DisplayPort
DisplayPort
and was originally intended to be an all-fiber interface, but due to early difficulties in creating a consumer-friendly fiber interconnect, nearly all implementations are copper systems. A notable exception, the Sony VAIO Z VPC-Z2, uses a nonstandard USB
USB
port with an optical component to connect to an outboard PCIe display adapter. Apple has been the primary driver of Thunderbolt adoption through 2011, though several other vendors[54] have announced new products and systems featuring Thunderbolt. Mobile PCIe specification (abbreviated to M-PCIe) allows PCI Express architecture to operate over the MIPI Alliance's M-PHY
M-PHY
physical layer technology. Building on top of already existing widespread adoption of M-PHY
M-PHY
and its low-power design, Mobile PCIe allows PCI Express
PCI Express
to be used in tablets and smartphones.[55] OCuLink (standing for "optical-copper link", since Cu is the chemical symbol for Copper) is an extension for the "cable version of PCI Express", acting as a competitor to version 3 of the Thunderbolt interface. Version 1.0 of OCuLink, released in Oct 2015, supports up to PCIe 3.0 x4 lanes (8 GT/s, 3.9 GB/s) over copper cabling; a fiber optic version may appear in the future.[28][56] Hardware protocol summary[edit] The PCIe link is built around dedicated unidirectional couples of serial (1-bit), point-to-point connections known as lanes. This is in sharp contrast to the earlier PCI connection, which is a bus-based system where all the devices share the same bidirectional, 32-bit or 64-bit parallel bus. PCI Express
PCI Express
is a layered protocol, consisting of a transaction layer, a data link layer, and a physical layer. The Data Link Layer is subdivided to include a media access control (MAC) sublayer. The Physical Layer is subdivided into logical and electrical sublayers. The Physical logical-sublayer contains a physical coding sublayer (PCS). The terms are borrowed from the IEEE 802
IEEE 802
networking protocol model. Physical layer[edit]

Card pins and lengths

Lanes Pins Length

Total Variable Total Variable

×1 2×18 = 36[57] 2×7 = 14 25 mm 7.65 mm

×4 2×32 = 64 2×21 = 42 39 mm 21.65 mm

×8 2×49 = 98 2×38 = 76 56 mm 38.65 mm

×16 2×82 = 164 2×71 = 142 89 mm 71.65 mm

An open-end PCI Express
PCI Express
×1 connector, allowing longer cards capable of using more lanes to be plugged while operating at ×1 speeds

The PCIe Physical Layer (PHY, PCIEPHY, PCI Express
PCI Express
PHY, or PCIe PHY) specification is divided into two sub-layers, corresponding to electrical and logical specifications. The logical sublayer is sometimes further divided into a MAC sublayer and a PCS, although this division is not formally part of the PCIe specification. A specification published by Intel, the PHY Interface for PCI Express (PIPE),[58] defines the MAC/PCS functional partitioning and the interface between these two sub-layers. The PIPE specification also identifies the physical media attachment (PMA) layer, which includes the serializer/deserializer (SerDes) and other analog circuitry; however, since SerDes
SerDes
implementations vary greatly among ASIC vendors, PIPE does not specify an interface between the PCS and PMA. At the electrical level, each lane consists of two unidirectional LVDS pairs operating at 2.5, 5, 8 or 16 Gbit/s, depending on the negotiated capabilities. Transmit and receive are separate differential pairs, for a total of four data wires per lane. A connection between any two PCIe devices is known as a link, and is built up from a collection of one or more lanes. All devices must minimally support single-lane (×1) link. Devices may optionally support wider links composed of 2, 4, 8, 12, 16, or 32 lanes. This allows for very good compatibility in two ways:

A PCIe card physically fits (and works correctly) in any slot that is at least as large as it is (e.g., an ×1 sized card will work in any sized slot); A slot of a large physical size (e.g., ×16) can be wired electrically with fewer lanes (e.g., ×1, ×4, ×8, or ×12) as long as it provides the ground connections required by the larger physical slot size.

In both cases, PCIe negotiates the highest mutually supported number of lanes. Many graphics cards, motherboards and BIOS
BIOS
versions are verified to support ×1, ×4, ×8 and ×16 connectivity on the same connection. Even though the two would be signal-compatible, it is not usually possible to place a physically larger PCIe card (e.g., a ×16 sized card) into a smaller slot – though if the PCIe slots are altered or a riser is used most motherboards will allow this. The width of a PCIe connector is 8.8 mm, while the height is 11.25 mm, and the length is variable. The fixed section of the connector is 11.65 mm in length and contains two rows of 11 (22 pins total), while the length of the other section is variable depending on the number of lanes. The pins are spaced at 1 mm intervals, and the thickness of the card going into the connector is 1.8 mm.[59][60] Data transmission[edit] PCIe sends all control messages, including interrupts, over the same links used for data. The serial protocol can never be blocked, so latency is still comparable to conventional PCI, which has dedicated interrupt lines. Data transmitted on multiple-lane links is interleaved, meaning that each successive byte is sent down successive lanes. The PCIe specification refers to this interleaving as data striping. While requiring significant hardware complexity to synchronize (or deskew) the incoming striped data, striping can significantly reduce the latency of the nth byte on a link. While the lanes are not tightly synchronized, there is a limit to the lane to lane skew of 20/8/6 ns for 2.5/5/8 GT/s so the hardware buffers can re-align the striped data.[61] Due to padding requirements, striping may not necessarily reduce the latency of small data packets on a link. As with other high data rate serial transmission protocols, the clock is embedded in the signal. At the physical level, PCI Express
PCI Express
2.0 utilizes the 8b/10b
8b/10b
encoding scheme[32] to ensure that strings of consecutive identical digits (zeros or ones) are limited in length. This coding was used to prevent the receiver from losing track of where the bit edges are. In this coding scheme every eight (uncoded) payload bits of data are replaced with 10 (encoded) bits of transmit data, causing a 20% overhead in the electrical bandwidth. To improve the available bandwidth, PCI Express
PCI Express
version 3.0 instead uses 128b/130b
128b/130b
encoding with scrambling. 128b/130b
128b/130b
encoding relies on the scrambling to limit the run length of identical-digit strings in data streams and ensure the receiver stays synchronised to the transmitter. It also reduces electromagnetic interference (EMI) by preventing repeating data patterns in the transmitted data stream. Data link layer[edit] The data link layer performs three vital services for the PCIe express link:

sequence the transaction layer packets (TLPs) that are generated by the transaction layer, ensure reliable delivery of TLPs between two endpoints via an acknowledgement protocol (ACK and NAK signaling) that explicitly requires replay of unacknowledged/bad TLPs, initialize and manage flow control credits

On the transmit side, the data link layer generates an incrementing sequence number for each outgoing TLP. It serves as a unique identification tag for each transmitted TLP, and is inserted into the header of the outgoing TLP. A 32-bit cyclic redundancy check code (known in this context as Link CRC or LCRC) is also appended to the end of each outgoing TLP. On the receive side, the received TLP's LCRC and sequence number are both validated in the link layer. If either the LCRC check fails (indicating a data error), or the sequence-number is out of range (non-consecutive from the last valid received TLP), then the bad TLP, as well as any TLPs received after the bad TLP, are considered invalid and discarded. The receiver sends a negative acknowledgement message (NAK) with the sequence-number of the invalid TLP, requesting re-transmission of all TLPs forward of that sequence-number. If the received TLP passes the LCRC check and has the correct sequence number, it is treated as valid. The link receiver increments the sequence-number (which tracks the last received good TLP), and forwards the valid TLP to the receiver's transaction layer. An ACK message is sent to remote transmitter, indicating the TLP was successfully received (and by extension, all TLPs with past sequence-numbers.) If the transmitter receives a NAK message, or no acknowledgement (NAK or ACK) is received until a timeout period expires, the transmitter must retransmit all TLPs that lack a positive acknowledgement (ACK). Barring a persistent malfunction of the device or transmission medium, the link-layer presents a reliable connection to the transaction layer, since the transmission protocol ensures delivery of TLPs over an unreliable medium. In addition to sending and receiving TLPs generated by the transaction layer, the data-link layer also generates and consumes DLLPs, data link layer packets. ACK and NAK signals are communicated via DLLPs, as are some power management messages and flow control credit information (on behalf of the transaction layer). In practice, the number of in-flight, unacknowledged TLPs on the link is limited by two factors: the size of the transmitter's replay buffer (which must store a copy of all transmitted TLPs until the remote receiver ACKs them), and the flow control credits issued by the receiver to a transmitter. PCI Express
PCI Express
requires all receivers to issue a minimum number of credits, to guarantee a link allows sending PCIConfig TLPs and message TLPs. Transaction layer[edit] PCI Express
PCI Express
implements split transactions (transactions with request and response separated by time), allowing the link to carry other traffic while the target device gathers data for the response. PCI Express
PCI Express
uses credit-based flow control. In this scheme, a device advertises an initial amount of credit for each received buffer in its transaction layer. The device at the opposite end of the link, when sending transactions to this device, counts the number of credits each TLP consumes from its account. The sending device may only transmit a TLP when doing so does not make its consumed credit count exceed its credit limit. When the receiving device finishes processing the TLP from its buffer, it signals a return of credits to the sending device, which increases the credit limit by the restored amount. The credit counters are modular counters, and the comparison of consumed credits to credit limit requires modular arithmetic. The advantage of this scheme (compared to other methods such as wait states or handshake-based transfer protocols) is that the latency of credit return does not affect performance, provided that the credit limit is not encountered. This assumption is generally met if each device is designed with adequate buffer sizes. PCIe 1.x is often quoted to support a data rate of 250 MB/s in each direction, per lane. This figure is a calculation from the physical signaling rate (2.5 gigabaud) divided by the encoding overhead (10 bits per byte.) This means a sixteen lane (×16) PCIe card would then be theoretically capable of 16×250 MB/s = 4 GB/s in each direction. While this is correct in terms of data bytes, more meaningful calculations are based on the usable data payload rate, which depends on the profile of the traffic, which is a function of the high-level (software) application and intermediate protocol levels. Like other high data rate serial interconnect systems, PCIe has a protocol and processing overhead due to the additional transfer robustness (CRC and acknowledgements). Long continuous unidirectional transfers (such as those typical in high-performance storage controllers) can approach >95% of PCIe's raw (lane) data rate. These transfers also benefit the most from increased number of lanes (×2, ×4, etc.) But in more typical applications (such as a USB
USB
or Ethernet
Ethernet
controller), the traffic profile is characterized as short data packets with frequent enforced acknowledgements.[62] This type of traffic reduces the efficiency of the link, due to overhead from packet parsing and forced interrupts (either in the device's host interface or the PC's CPU). Being a protocol for devices connected to the same printed circuit board, it does not require the same tolerance for transmission errors as a protocol for communication over longer distances, and thus, this loss of efficiency is not particular to PCIe. Applications[edit]

Asus
Asus
Nvidia
Nvidia
GeForce GTX 650 Ti, a PCI Express
PCI Express
3.0 ×16 graphics card

Intel
Intel
82574L Gigabit Ethernet
Gigabit Ethernet
NIC, a PCI Express
PCI Express
×1 card

A Marvell-based SATA 3.0 controller, as a PCI Express
PCI Express
×1 card

PCI Express
PCI Express
operates in consumer, server, and industrial applications, as a motherboard-level interconnect (to link motherboard-mounted peripherals), a passive backplane interconnect and as an expansion card interface for add-in boards. In virtually all modern (as of 2012[update]) PCs, from consumer laptops and desktops to enterprise data servers, the PCIe bus serves as the primary motherboard-level interconnect, connecting the host system-processor with both integrated-peripherals (surface-mounted ICs) and add-on peripherals (expansion cards). In most of these systems, the PCIe bus co-exists with one or more legacy PCI buses, for backward compatibility with the large body of legacy PCI peripherals. As of 2013[update] PCI Express
PCI Express
has replaced AGP as the default interface for graphics cards on new systems. Almost all models of graphics cards released since 2010 by AMD (ATI) and Nvidia
Nvidia
use PCI Express. Nvidia
Nvidia
uses the high-bandwidth data transfer of PCIe for its Scalable Link Interface
Scalable Link Interface
(SLI) technology, which allows multiple graphics cards of the same chipset and model number to run in tandem, allowing increased performance. AMD has also developed a multi-GPU system based on PCIe called CrossFire. AMD and Nvidia
Nvidia
have released motherboard chipsets that support as many as four PCIe ×16 slots, allowing tri-GPU and quad-GPU card configurations. External GPUs[edit] Theoretically, external PCIe could give a notebook the graphics power of a desktop, by connecting a notebook with any PCIe desktop video card (enclosed in its own external housing, with strong power supply and cooling); possible with an ExpressCard
ExpressCard
interface or a Thunderbolt interface. The ExpressCard
ExpressCard
interface provides bit rates of 5 Gbit/s (0.5 GB/s throughput), whereas the Thunderbolt interface provides bit rates of up to 40 Gbit/s (5 GB/s throughput). In 2017 more fully featured external card hubs were introduced. An example for this year, with a full-length PCIe x16 interface, is the Razer Core [63]. In 2010 external card hubs were introduced that can connect to a laptop or desktop through a PCI ExpressCard
ExpressCard
slot. These hubs can accept full-sized graphics cards. Examples include MSI GUS,[64] Village Instrument's ViDock,[65] the Asus
Asus
XG Station, Bplus PE4H V3.2 adapter,[66] as well as more improvised DIY devices.[67] However such solutions are limited by the size (often only x1) and version of the available PCIe slot on a laptop. In 2008, AMD announced the ATI XGP technology, based on a proprietary cabling system that is compatible with PCIe ×8 signal transmissions.[68] This connector is available on the Fujitsu Amilo and the Acer Ferrari One notebooks. Fujitsu launched their AMILO GraphicBooster enclosure for XGP soon thereafter.[69] Around 2010 Acer launched the Dynavivid graphics dock for XGP.[70] Intel
Intel
Thunderbolt interface has given opportunity to new and faster products to connect with a PCIe card externally. Magma has released the ExpressBox 3T, which can hold up to three PCIe cards (two at ×8 and one at ×4).[71] MSI also released the Thunderbolt GUS II, a PCIe chassis dedicated for video cards.[72] Other products such as the Sonnet’s Echo Express[73] and mLogic’s mLink are Thunderbolt PCIe chassis in a smaller form factor.[74] However, all these products require a computer with a Thunderbolt port (i.e., Thunderbolt devices), such as Apple's MacBook Pro
MacBook Pro
models released in late 2013. For the professional market, Nvidia
Nvidia
has developed the Quadro Plex external PCIe family of GPUs that can be used for advanced graphic applications. These video cards require a PCI Express
PCI Express
×8 or ×16 slot for the host-side card which connects to the Plex via a VHDCI
VHDCI
carrying eight PCIe lanes.[75] Storage devices[edit]

An OCZ
OCZ
RevoDrive SSD, a full-height ×4 PCI Express
PCI Express
card

See also: SATA Express
SATA Express
and NVM Express PCI Express
PCI Express
protocol can be used as data interface to flash memory devices, such as memory cards and solid-state drives (SSDs). XQD card
XQD card
is a memory card format utilizing PCI Express, developed by the CompactFlash Association, with transfer rates of up to 500 MB/s.[76] Many high-performance, enterprise-class SSDs are designed as PCI Express RAID controller
RAID controller
cards with flash memory chips placed directly on the circuit board, utilizing proprietary interfaces and custom drivers to communicate with the operating system; this allows much higher transfer rates (over 1 GB/s) and IOPS (over one million I/O operations per second) when compared to Serial ATA
Serial ATA
or SAS drives.[77][78] For example, in 2011 OCZ
OCZ
and Marvell co-developed a native PCI Express
PCI Express
solid-state drive controller for a PCI Express
PCI Express
3.0 ×16 slot with maximum capacity of 12 TB and a performance of to 7.2 GB/s sequential transfers and up to 2.52 million IOPS in random transfers.[79] SATA Express
SATA Express
is an interface for connecting SSDs, by providing multiple PCI Express
PCI Express
lanes as a pure PCI Express
PCI Express
connection to the attached storage device.[80] M.2
M.2
is a specification for internally mounted computer expansion cards and associated connectors, which also uses multiple PCI Express
PCI Express
lanes.[81] PCI Express
PCI Express
storage devices can implement both AHCI logical interface for backward compatibility, and NVM Express
NVM Express
logical interface for much faster I/O operations provided by utilizing internal parallelism offered by such devices. Enterprise-class SSDs can also implement SCSI over PCI Express.[82] Cluster interconnect[edit] Certain data-center applications (such as large computer clusters) require the use of fiber-optic interconnects due to the distance limitations inherent in copper cabling. Typically, a network-oriented standard such as Ethernet
Ethernet
or Fibre Channel
Fibre Channel
suffices for these applications, but in some cases the overhead introduced by routable protocols is undesirable and a lower-level interconnect, such as InfiniBand, RapidIO, or NUMAlink is needed. Local-bus standards such as PCIe and HyperTransport
HyperTransport
can in principle be used for this purpose,[83] but as of 2015[update] solutions are only available from niche vendors such as Dolphin ICS. Competing protocols[edit] Other communications standards based on high bandwidth serial architectures include InfiniBand, RapidIO, HyperTransport, Intel QuickPath Interconnect, and the Mobile Industry Processor Interface (MIPI). The differences are based on the trade-offs between flexibility and extensibility vs latency and overhead. For example, adding complex header information to a transmitted packet allows for complex routing ( PCI Express
PCI Express
is capable of this through an optional End-to-End TLP Prefix feature[84]). The additional overhead reduces the effective bandwidth of the interface and complicates bus discovery and initialization software. Also making the system hot-pluggable requires that software track network topology changes. InfiniBand
InfiniBand
is such a technology. Another example is making the packets shorter to decrease latency (as is required if a bus must operate as a memory interface). Smaller packets mean packet headers consume a higher percentage of the packet, thus decreasing the effective bandwidth. Examples of bus protocols designed for this purpose are RapidIO
RapidIO
and HyperTransport. PCI Express
PCI Express
falls somewhere in the middle, targeted by design as a system interconnect (local bus) rather than a device interconnect or routed network protocol. Additionally, its design goal of software transparency constrains the protocol and raises its latency somewhat. Delays in PCIe 4.0 implementations led to the Gen-Z
Gen-Z
consortium, the CCIX[85] effort and an open Coherent Accelerator Processor Interface (CAPI) all being announced by the end of 2016.[86] See also[edit]

Electronics portal

Active State Power Management (ASPM) Conventional PCI PCI configuration space PCI-X PCI/104-Express PCIe/104 Root complex Serial Digital Video Out (SDVO) List of device bit rates § Main buses

Notes[edit]

^ The card's Serial ATA
Serial ATA
power connector is present because the USB 3.0 ports require more power than the PCI Express
PCI Express
bus can supply. More often, a 4-pin Molex power connector is used.

References[edit]

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Further reading[edit]

Budruk, Ravi; Anderson, Don; Shanley, Tom (2003), Winkles, Joseph ‘Joe’, ed., PCI Express
PCI Express
System Architecture, Mind share PC system architecture, Addison-Wesley, ISBN 978-0-321-15630-3  1120 pp. Solari, Edward; Congdon, Brad (2003), Complete PCI Express
PCI Express
Reference: Design Implications for Hardware and Software Developers, Intel, ISBN 978-0-9717861-9-6 , 1056 pp. Wilen, Adam; Schade, Justin P; Thornburg, Ron (Apr 2003), Introduction to PCI Express: A Hardware and Software Developer's Guide, Intel, ISBN 978-0-9702846-9-3 , 325 pp.

External links[edit]

PCI-SIG , the industry organization that maintains and develops the various PCI standards

PCI-Express Specification, PCI-SIG  " PCI Express
PCI Express
Base Specification Revision 1.0". PCI-SIG. 29 April 2002. (Subscription required (help)). 

" PCI Express
PCI Express
Architecture", Developer Network, Intel  Introduction to PCI Protocol, Electro Friends  An introduction to how PCIe works at the TLP level, Xilly Bus  PCI Express
PCI Express
Basics, 2007, by Ravi Budruk, MindShare, Inc. PCI Express
PCI Express
Atomic Operations (also known as "AtomicOps") PCI Express
PCI Express
2.0 Electrical Specification, 2006, by Jeff Morriss and Gerry Talbot

v t e

Technical and de facto standards for wired computer buses

General

System bus Front-side bus Back-side bus Daisy chain Control bus Address bus Bus contention Network on a chip Plug and play List of bus bandwidths

Standards

SS-50 bus S-100 bus Multibus Unibus VAXBI MBus STD Bus SMBus Q-Bus Europe Card Bus ISA STEbus Zorro II Zorro III CAMAC FASTBUS LPC HP Precision Bus EISA VME VXI VXS NuBus TURBOchannel MCA SBus VLB PCI PXI HP GSC bus InfiniBand UPA PCI Extended (PCI-X) AGP PCI Express
PCI Express
(PCIe) Direct Media Interface (DMI) RapidIO Intel
Intel
QuickPath Interconnect NVLink HyperTransport

Infinity Fabric

Intel
Intel
UltraPath Interconnect

Storage

ST-506 ESDI IPI SMD Parallel ATA
Parallel ATA
(PATA) SSA DSSI HIPPI Serial ATA
Serial ATA
(SATA) SCSI

Parallel SAS

Fibre Channel SATAe PCI Express
PCI Express
(via AHCI or NVMe logical device interface)

Peripheral

Apple Desktop Bus DCB HP-IL HIL MIDI RS-232 RS-422 RS-423 RS-485 DMX512-A IEEE-488
IEEE-488
(GPIB) IEEE-1284 (parallel port) UNI/O ACCESS.bus 1-Wire D²B I²C SPI Parallel SCSI Profibus IEEE 1394
IEEE 1394
(FireWire) USB Camera Link External PCIe Thunderbolt

Audio

ADAT Lightpipe AES3 Intel
Intel
HD Audio I²S MADI McASP S/PDIF TOSLINK

Portable

PC Card ExpressCard

Embedded

Multidrop bus CoreConnect AMBA Wishbone SLIMbus

Interfaces are listed by their speed in the (roughly) ascending order, so the interface at the end of each section should be the fastest. Category

v t e

Basic computer components

Input devices

Keyboard Image scanner Microphone Pointing device

Graphics tablet Joystick Light pen Mouse

Optical

Pointing stick Touchpad Touchscreen Trackball

Webcam

Softcam

Refreshable braille display

Output devices

Monitor Refreshable braille display Printer Speakers Plotter

Removable data storage

Optical disc

CD DVD Blu-ray

Disk pack Floppy disk Memory card USB
USB
flash drive

Computer
Computer
case

Central processing unit
Central processing unit
(CPU) HDD / SSD / SSHD Motherboard Network interface controller Power supply Random-access memory
Random-access memory
(RAM) Sound card Video card Fax modem Expansion card

Ports

Ethernet FireWire
FireWire
(IEEE 1394) Parallel port Serial port PS/2 port USB Thunderbolt HDMI
HDMI
/ DVI / VG

.