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HyperTransport (HT), formerly known as Lightning Data Transport, is a technology for interconnection of computer
processor Processor may refer to: Computing Hardware * Processor (computing) **Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (I ...
s. It is a bidirectional serial/
parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of IB ...
high-
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
, low- latency
point-to-point link In telecommunications, a point-to-point connection refers to a communications connection between two communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one c ...
that was introduced on April 2, 2001. The HyperTransport Consortium is in charge of promoting and developing HyperTransport technology. HyperTransport is best known as the system bus architecture of
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufact ...
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
s (CPUs) from
Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
through
AMD FX AMD FX was a series of high-end AMD microprocessors for personal computers which debuted in 2011, claimed as AMD's first native 8-core desktop processor. The line was introduced with the Bulldozer microarchitecture at launch (codename Zambezi), ...
and the associated motherboard chipsets. HyperTransport has also been used by IBM and Apple for the Power Mac G5 machines, as well as a number of modern MIPS systems. The current specification HTX 3.1 remained competitive for 2014 high-speed (2666 and 3200  MT/s or about 10.4 GB/s and 12.8 GB/s) DDR4 RAM and slower (around 1 GB/

similar to high end Solid-state drive#Standard card form factors, PCIe SSDs
ULLtraDIMM The ULLtraDIMM is a solid state storage device from SanDisk that connects flash storage directly onto the DDR3 memory bus. Unlike traditional PCIe Flash Storage devices, the ULLtraDIMM is plugged directly into an industry standard RDIMM memory ...
flash RAM) technology—a wider range of RAM speeds on a common CPU bus than any Intel front-side bus. Intel technologies require each speed range of RAM to have its own interface, resulting in a more complex motherboard layout but with fewer bottlenecks. HTX 3.1 at 26 GB/s can serve as a unified bus for as many as four DDR4 sticks running at the fastest proposed speeds. Beyond that DDR4 RAM may require two or more HTX 3.1 buses diminishing its value as unified transport.


Overview


Links and rates

HyperTransport comes in four versions—1.x, 2.0, 3.0, and 3.1—which run from 200
MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
to 3.2 GHz. It is also a DDR or " double data rate" connection, meaning it sends data on both the rising and falling edges of the
clock signal In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock sign ...
. This allows for a maximum data rate of 6400 MT/s when running at 3.2 GHz. The operating frequency is autonegotiated with the motherboard chipset (North Bridge) in current computing. HyperTransport supports an autonegotiated bit width, ranging from 2 to 32 bits per link; there are two unidirectional links per HyperTransport bus. With the advent of version 3.1, using full
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
links and utilizing the full HyperTransport 3.1 specification's operating frequency, the theoretical transfer rate is 25.6  GB/s (3.2 GHz × 2 transfers per clock cycle × 32 bits per link) per direction, or 51.2 GB/s aggregated throughput, making it faster than most existing bus standard for PC workstations and servers as well as making it faster than most bus standards for high-performance computing and networking. Links of various widths can be mixed together in a single system configuration as in one
16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...
link to another CPU and one
8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses ...
link to a peripheral device, which allows for a wider interconnect between
CPUs A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
, and a lower bandwidth interconnect to
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...
s as appropriate. It also supports link splitting, where a single 16-bit link can be divided into two 8-bit links. The technology also typically has lower latency than other solutions due to its lower overhead. Electrically, HyperTransport is similar to low-voltage differential signaling (LVDS) operating at 1.2 V. HyperTransport 2.0 added post-cursor transmitter
deemphasis Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted. This is referred to as "pre-emphasis"before the process the signal will u ...
. HyperTransport 3.0 added scrambling and receiver phase alignment as well as optional transmitter precursor deemphasis.


Packet-oriented

HyperTransport is
packet Packet may refer to: * A small container or pouch ** Packet (container), a small single use container ** Cigarette packet ** Sugar packet * Network packet, a formatted unit of data carried by a packet-mode computer network * Packet radio, a form ...
-based, where each packet consists of a set of
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
words, regardless of the physical width of the link. The first word in a packet always contains a command field. Many packets contain a 40-bit address. An additional 32-bit control packet is prepended when 64-bit addressing is required. The data payload is sent after the control packet. Transfers are always padded to a multiple of 32 bits, regardless of their actual length. HyperTransport packets enter the interconnect in segments known as bit times. The number of bit times required depends on the link width. HyperTransport also supports system management messaging, signaling interrupts, issuing probes to adjacent devices or processors, I/O transactions, and general data transactions. There are two kinds of write commands supported: posted and non-posted. Posted writes do not require a response from the target. This is usually used for high bandwidth devices such as uniform memory access traffic or direct memory access transfers. Non-posted writes require a response from the receiver in the form of a "target done" response. Reads also require a response, containing the read data. HyperTransport supports the PCI consumer/producer ordering model.


Power-managed

HyperTransport also facilitates
power management Power management is a feature of some electrical appliances, especially copiers, computers, computer CPUs, computer GPUs and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power sta ...
as it is compliant with the
Advanced Configuration and Power Interface Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto con ...
specification. This means that changes in processor sleep states (C states) can signal changes in device states (D states), e.g. powering off disks when the CPU goes to sleep. HyperTransport 3.0 added further capabilities to allow a centralized power management controller to implement power management policies.


Applications


Front-side bus replacement

The primary use for HyperTransport is to replace the Intel-defined front-side bus, which is different for every type of Intel processor. For instance, a Pentium cannot be plugged into a PCI Express bus directly, but must first go through an adapter to expand the system. The proprietary front-side bus must connect through adapters for the various standard buses, like AGP or PCI Express. These are typically included in the respective controller functions, namely the '' northbridge'' and '' southbridge''. In contrast, HyperTransport is an open specification, published by a multi-company consortium. A single HyperTransport adapter chip will work with a wide spectrum of HyperTransport enabled microprocessors.
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufact ...
used HyperTransport to replace the front-side bus in their Opteron,
Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
,
Athlon II Athlon II is a family of AMD multi-core 45 nm central processing units, which is aimed at the budget to mid-range market and is a complementary product lineup to the Phenom II. Features The Athlon II series is based on the AMD K10 architectu ...
, Sempron 64, Turion 64, Phenom, Phenom II and FX families of microprocessors.


Multiprocessor interconnect

Another use for HyperTransport is as an interconnect for NUMA multiprocessor computers. AMD used HyperTransport with a proprietary
cache coherency In computer architecture, cache coherence is the uniformity of shared resource data that ends up stored in multiple local caches. When clients in a system maintain caches of a common memory resource, problems may arise with incoherent data, whi ...
extension as part of their Direct Connect Architecture in their Opteron and
Athlon 64 FX The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
( Dual Socket Direct Connect (DSDC) Architecture) line of processors.
Infinity Fabric HyperTransport (HT), formerly known as Lightning Data Transport, is a technology for interconnection of computer processors. It is a bidirectional serial/ parallel high- bandwidth, low- latency point-to-point link that was introduced on Apri ...
used with the EPYC server CPUs is a superset of HyperTransport. The HORUS interconnect from
Newisys Newisys was an American technology company. At various times it sold computers for data centers (known as servers), and computer data storage products. It operated as a subsidiary of Sanmina Corporation since 2004. History Newisys was founded in ...
extends this concept to larger clusters. The Aqua device from 3Leaf Systems virtualizes and interconnects CPUs, memory, and I/O.


Router or switch bus replacement

HyperTransport can also be used as a bus in routers and switches. Routers and switches have multiple network interfaces, and must forward data between these ports as fast as possible. For example, a four-port, 1000 
Mbit The megabit is a multiple of the unit bit for digital information. The prefix mega (symbol M) is defined in the International System of Units (SI) as a multiplier of 106 (1 million), and therefore :1 megabit = = = 1000 kilobits. The megabit ...
/s Ethernet router needs a maximum 8000 Mbit/s of internal bandwidth (1000 Mbit/s × 4 ports × 2 directions)—HyperTransport greatly exceeds the bandwidth this application requires. However a 4 + 1 port 10 Gb router would require 100 Gbit/s of internal bandwidth. Add to that 802.11ac 8 antennas and the WiGig 60 GHz standard (802.11ad) and HyperTransport becomes more feasible (with anywhere between 20 and 24 lanes used for the needed bandwidth).


Co-processor interconnect

The issue of latency and bandwidth between CPUs and co-processors has usually been the major stumbling block to their practical implementation. Co-processors such as
FPGAs A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware de ...
have appeared that can access the HyperTransport bus and become integrated on the motherboard. Current generation FPGAs from both main manufacturers (
Altera Altera Corporation was a manufacturer of programmable logic devices (PLDs) headquartered in San Jose, California. It was founded in 1983 and acquired by Intel in 2015. The main product lines from Altera were the flagship Stratix series, mid-rang ...
and Xilinx) directly support the HyperTransport interface, and have IP Cores available. Companies such as XtremeData, Inc. and DRC take these FPGAs (Xilinx in DRC's case) and create a module that allows FPGAs to plug directly into the Opteron socket. AMD started an initiative named
Torrenza Torrenza was an initiative announced by Advanced Micro Devices (AMD) in 2006 to improve support for the integration of specialized coprocessors in systems based on AMD Opteron microprocessors. Torrenza does not refer to a specific product or specifi ...
on September 21, 2006 to further promote the usage of HyperTransport for plug-in cards and
coprocessors A coprocessor is a computer processor used to supplement the functions of the primary processor (the CPU). Operations performed by the coprocessor may be floating-point arithmetic, graphics, signal processing, string processing, cryptography or ...
. This initiative opened their "Socket F" to plug-in boards such as those from XtremeData and DRC.


Add-on card connector (HTX and HTX3)

A connector specification that allows a slot-based peripheral to have direct connection to a microprocessor using a HyperTransport interface was released by the HyperTransport Consortium. It is known as HyperTransport eXpansion (HTX). Using a reversed instance of the same mechanical connector as a 16-lane PCI Express slot (plus an x1 connector for power pins), HTX allows development of plug-in cards that support direct access to a CPU and DMA to the system RAM. The initial card for this slot was the QLogic InfiniPath InfiniBand HCA. IBM and HP, among others, have released HTX compliant systems. The original HTX standard is limited to 16bits and 800MHz. In August 2008, the HyperTransport Consortium released HTX3, which extends the clock rate of HTX to 2.6 GHz (5.2 GT/s, 10.7 GTi, 5.2 real GHz data rate, 3 MT/s edit rate) and retains backwards compatibility.


Testing

The "DUT" test connector is defined to enable standardized functional test system interconnection.


Implementations

*
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufact ...
AMD64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging m ...
and Direct Connect Architecture based
CPUs A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
*
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufact ...
chipsets ** AMD-8000 series ** AMD 480 series ** AMD 580 series ** AMD 690 series ** AMD 700 series ** AMD 800 series ** AMD 900 series *
ATI Ati or ATI may refer to: * Ati people, a Negrito ethnic group in the Philippines **Ati language (Philippines), the language spoken by this people group ** Ati-Atihan festival, an annual celebration held in the Philippines *Ati language (China), a ...
chipsets ** ATI Radeon Xpress 200 for AMD processor ** ATI Radeon Xpress 3200 for AMD processor *
Broadcom Broadcom Inc. is an American designer, developer, manufacturer and global supplier of a wide range of semiconductor and infrastructure software products. Broadcom's product offerings serve the data center, networking, software, broadband, wirel ...
(then ServerWorks) HyperTransport SystemI/O controllers ** HT-2000 ** HT-2100 *
Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
QuantumFlow Processors * ht_tunnel from OpenCores project (MPL licence) * IBM CPC925 and CPC945 ( PowerPC 970 northbridges) chipsets *
Loongson Loongson () is the name of a family of general-purpose, MIPS architecture-compatible microprocessors, as well as the name of the Chinese fabless company (Loongson Technology) that develops them. The processors are alternately called Godson proc ...
-3 MIPS processor *
Nvidia Nvidia CorporationOfficially written as NVIDIA and stylized in its logo as VIDIA with the lowercase "n" the same height as the uppercase "VIDIA"; formerly stylized as VIDIA with a large italicized lowercase "n" on products from the mid 1990s to ...
nForce chipsets ** nForce Professional MCPs (Media and Communication Processor) ** nForce 3 series **
nForce 4 The nForce4 is a motherboard chipset released by Nvidia in October 2004. The chipset supports AMD 64-bit processors (Socket 939, Socket AM2 and Socket 754) and Intel Pentium 4 LGA 775 processors. Models nForce4/nForce4-4x nForce4 is the second ...
series ** nForce 500 series ** nForce 600 series ** nForce 700 series ** nForce 900 series *
PMC-Sierra PMC-Sierra was a global fabless semiconductor company with offices worldwide that developed and sold semiconductor devices into the storage, communications, optical networking, printing, and embedded computing marketplaces. On January 15, 2016, ...
RM9000X2 MIPS CPU * Power Mac G5 * Raza Thread Processors * SiByte MIPS CPUs from
Broadcom Broadcom Inc. is an American designer, developer, manufacturer and global supplier of a wide range of semiconductor and infrastructure software products. Broadcom's product offerings serve the data center, networking, software, broadband, wirel ...
* Transmeta TM8000 Efficeon CPUs * VIA chipsets K8 series


Frequency specifications

* AMD
Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
, Athlon 64 FX, Athlon 64 X2, Athlon X2,
Athlon II Athlon II is a family of AMD multi-core 45 nm central processing units, which is aimed at the budget to mid-range market and is a complementary product lineup to the Phenom II. Features The Athlon II series is based on the AMD K10 architectu ...
, Phenom, Phenom II, Sempron, Turion series and later use one 16-bit HyperTransport link. AMD Athlon 64 FX ( 1207), Opteron use up to three 16-bit HyperTransport links. Common clock rates for these processor links are 800 MHz to 1 GHz (older single and multi socket systems on 754/939/940 links) and 1.6 GHz to 2.0 GHz (newer single socket systems on AM2+/AM3 links—most newer CPUs using 2.0GHz). While HyperTransport itself is capable of 32-bit width links, that width is not currently utilized by any AMD processors. Some chipsets though do not even utilize the 16-bit width used by the processors. Those include the Nvidia
nForce3 The nForce3 chipset was created by Nvidia as a Media and Communications Processor. Specifically, it was designed for use with the Athlon 64 processor. Features of the nForce3 When the Athlon 64 was launched, the Nvidia nForce3 Pro150 and V ...
150, nForce3 Pro 150, and the ULi M1689—which use a 16-bit HyperTransport downstream link but limit the HyperTransport upstream link to 8 bits.


Name

There has been some marketing confusion between the use of HT referring to HyperTransport and the later use of HT to refer to Intel's Hyper-Threading feature on some Pentium 4-based and the newer Nehalem and Westmere-based
Intel Core Intel Core is a line of streamlined midrange consumer, workstation and enthusiast computer central processing units (CPUs) marketed by Intel Corporation. These processors displaced the existing mid- to high-end Pentium processors at the time ...
microprocessors. Hyper-Threading is officially known as Hyper-Threading Technology (HTT) or HT Technology. Because of this potential for confusion, the HyperTransport Consortium always uses the written-out form: "HyperTransport."


Infinity Fabric

Infinity Fabric (IF) is a superset of HyperTransport announced by AMD in 2016 as an interconnect for its GPUs and CPUs. It is also usable as interchip interconnect for communication between CPUs and GPUs (for Heterogeneous System Architecture), an arrangement known as Infinity Architecture. The company said the Infinity Fabric would scale from 30GB/s to 512GB/s, and be used in the
Zen Zen ( zh, t=禪, p=Chán; ja, text= 禅, translit=zen; ko, text=선, translit=Seon; vi, text=Thiền) is a school of Mahayana Buddhism that originated in China during the Tang dynasty, known as the Chan School (''Chánzong'' 禪宗), and l ...
-based CPUs and Vega GPUs which were subsequently released in 2017. On Zen and
Zen+ Zen+ is the codename for a computer processor microarchitecture by AMD. It is the successor to the first gen Zen microarchitecture, first released in April 2018, powering the second generation of Ryzen processors, known as Ryzen 2000 for mainstre ...
CPUs, the "SDF" data interconnects are run at the same frequency as the DRAM memory clock (MEMCLK), a decision made to remove the latency caused by different clock speeds. As a result, using a faster RAM module makes the entire bus faster. The links are 32-bit wide, as in HT, but 8 transfers are done per cycle (128-bit packets) compared to the original 2. Electrical changes are made for higher power efficiency. On Zen 2 and
Zen 3 Zen 3 is the codename for a CPU microarchitecture by AMD, released on November 5, 2020. It is the successor to Zen 2 and uses TSMC's 7 nm process for the chiplets and GlobalFoundries's 14 nm process for the I/O die on the server chips and 12 nm ...
CPUs, the IF bus is on a separate clock, either in a 1:1 or 2:1 ratio to the DRAM clock, because of Zen's early problems with high-speed DRAM affecting IF speed, and therefore system stability. The bus width has also been doubled.


See also

* Elastic interface bus *
Fibre Channel Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data cent ...
* Front-side bus * Intel QuickPath Interconnect *
List of device bandwidths This is a list of interface bit rates, is a measure of information transfer rates, or digital bandwidth capacity, at which digital interfaces in a computer or network can communicate over various kinds of buses and channels. The distinction can ...
* PCI Express * RapidIO * AGESA


References


External links

* * . * * {{Computer-bus Computer buses Macintosh internals Serial buses