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Encyclopedia > Front side bus
A typical north/southbridge layout

In personal computers, the Front Side Bus (FSB) is the data transfer bus that carries information between the CPU and the northbridge of the Motherboard. Image File history File links Size of this preview: 382 × 600 pixel Image in higher resolution (800 × 1256 pixel, file size: 133 KB, MIME type: image/png) This is just a rasterization of the SVG version. ... Image File history File links Size of this preview: 382 × 600 pixel Image in higher resolution (800 × 1256 pixel, file size: 133 KB, MIME type: image/png) This is just a rasterization of the SVG version. ... PCI Express bus card slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 32-bit PCI bus card slot (bottom) In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers, and a bus... CPU redirects here. ... This article or section does not cite any references or sources. ...


Some computers also have a back side bus which connects the CPU to a memory cache. This bus and the cache memory connected to it are faster than accessing the system RAM via the front side bus. The back side bus is a computer bus used to connect the CPU with the L2 cache using a dual-bus architecture. ... Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ...


The bandwidth or maximum theoretical throughput of the front side bus is determined by the product of the width of its data path, its clock frequency (cycles per second) and the number of data transfers it performs per cycle or clock tick. For example, a 32-bit (4-byte) wide FSB operating at a frequency of 100 MHz that performs 4 transfers per tick has a bandwidth of 1600 megabytes per second (MB/s). Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ... Look up jiffy in Wiktionary, the free dictionary. ... This article is about the unit of information. ... For the computer industry magazine, see Byte (magazine). ... This article is about a unit of data. ...


The number of transfers per tick is dependent on the technology used. For example, GTL+ performs 1 transfer/tick, EV6 2 transfers/tick, and AGTL+ 4 transfers/tick. Intel calls the technique of 4 transfers per cycle Quad Pumping. Gunning Transceiver Logic or GTL is a type of logic signalling used to drive electronic backplane buses. ... Quad data rate (or quad pumping) is a communication signalling technique wherein data is transmitted at both the rising and falling edges of signals much the same way DDR technology works, but with two signals 90° out of phase from each other, effectively delivering 4 bits of data per clock...


Notice that many manufacturers publish the "speed" of the FSB in megatransfers per second (MT/s), not the FSB clock speed (in megahertz (MHz)). The MT/s rating is affected by how many transfers are performed each clock cycle. For example, if a motherboard has a FSB clocked at 266 MHz and performs 4 transfers per clock tick, the FSB is rated at 1066 MT/s. This is what some manufacturers publish as the "speed" of the FSB. Megatransfer is a term used in computer technology, referring to a number of data transfers (or operations). ...

Contents

History and Current usage

The front side bus has been a part of computer architecture since applications first started using more memory than a CPU could reasonably hold. CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ...


Most modern front side buses serve as a backbone between the CPU and a chipset. The chipset (usually a combination of a northbridge and a southbridge) is the connection point for all other buses in the system. Buses like the PCI, AGP, and memory buses all connect to the chipset in order for data to flow between the connected devices. These secondary system buses usually run at speeds derived from the front side bus speed. CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... Diagram of a motherboard chipset A chipset is a group of integrated circuits, or chips, that are designed to work together, and are usually marketed as a single product. ... This article or section does not cite any references or sources. ... This article does not cite any references or sources. ... This article is about the computer bus type. ... The Accelerated Graphics Port (also called Advanced Graphics Port, often shortened to AGP) is a high-speed point-to-point channel for attaching a graphics card to a computers motherboard, primarily to assist in the acceleration of 3D computer graphics. ...


In response to AMD's Torrenza initiative, Intel has opened its FSB CPU socket to third party devices [1][2]. Prior to this announcement, made in Spring 2007 at Intel Developer Forum in Beijing, Intel had very closely guarded who had access to the FSB, only allowing Intel processors in the CPU socket. This is now changing, the first example being FPGA co-processors, a result of collaboration between Intel-Xilinx-Nallatech [3] and Intel-Altera-XtremeData [4] [5]. Advanced Micro Devices, Inc. ... Torrenza is a technology developed by AMD that paves the way for specialised coprocessors to run in spare CPU sockets on multiway CPU systems. ... Intel Developer Forum (IDF), is a twice yearly gathering of technologists to discuss Intel products and products based around Intel products. ... Peking redirects here. ... A field-programmable gate array or FPGA is a gate array that can be reprogrammed after it is manufactured, rather than having its programming fixed during the manufacturing — a programmable logic device. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Xilinx, Inc. ... Nallatech is a Scottish computer hardware and software firm based in Cumbernauld in North Lanarkshire, Scotlandthat specializes in and is one of the world leaders in Field-programmable gate array microchip technology in FPGA Computing. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Altera headquarters in San Jose Altera Corporation (NASDAQ: ALTR) is a leading manufacturer of programmable logic devices. ...


Related Component Speeds

CPU

The frequency at which a processor (CPU) operates is determined by applying a clock multiplier to the front side bus (FSB) speed. For example, a processor running at 550 MHz might be using a 100 MHz FSB. This means there is an internal clock multiplier setting (also called bus/core ratio) of 5.5. That is, the CPU is set to run at 5.5 times the frequency of the front side bus: 100 MHz × 5.5 = 550 MHz. By varying either the FSB or the multiplier, different CPU speeds can be achieved. For other uses, see Frequency (disambiguation). ... MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ... The CPU multiplier is one way for processors to run much faster than the clock speed that the motherboard or RAM allows. ...


Memory

Setting a FSB speed is related directly to the speed grade of memory a system must use. The memory bus connects the northbridge and RAM, just as the front side bus connects the CPU and northbridge. Often, these two buses must operate at the same frequency. Increasing the front-side bus to 170 MHz in most cases also means running the memory at 170 MHz.


In newer systems, it is possible to see memory ratios of "4:5" and the like. The memory will run 5/4 times as fast as the FSB in this situation, meaning a 133 MHz bus can run with the memory at 166 MHz. This is often referred to as an 'asynchronous' system. It is important to realize that due to differences in CPU and system architecture, overall system performance can vary in unexpected ways with different FSB-to-memory ratios.


In complex image, audio, video, gaming, and scientific applications where the data set is large, FSB speed becomes a major performance issue. A slow FSB will cause the CPU to spend significant amounts of time waiting for data to arrive from system memory. Look up RAM, Ram, ram in Wiktionary, the free dictionary. ...


Peripheral Buses

Similar to the memory bus, the PCI and AGP buses can also be run asynchronously from the front side bus. In older systems, these buses operated at a set fraction of the front side bus frequency. This fraction was set by the BIOS. In newer systems the PCI, AGP, and PCI Express peripheral buses often receive their own clock signals, which eliminates their dependence on the front side bus for timing. This article is about the computer bus type. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ...


Overclocking

Overclocking is the practice of making computer components operate beyond their stock performance levels. AMD Athlon XP Overclocking BIOS Setup on ABIT NF7-S. FSB frequency (External clock) has increased from 133 MHz to 148 MHz, and clock multiplier factor has changed from 13. ...


Many motherboards allow the user to manually set the clock multiplier and FSB settings by changing jumpers or BIOS settings. Many CPU manufacturers now "lock" a preset multiplier setting into the chip. It is possible to unlock some locked CPUs; for instance, some Athlons can be unlocked by connecting electrical contacts across points on the CPU's surface. For all processors, increasing the FSB speed can be done to boost processing speed. For other uses, see Bios. ... Athlon is the brand name applied to a series of different x86 processors designed and manufactured by AMD. The original Athlon, or Athlon Classic, was the first seventh-generation x86 processor and, in a first, retained the initial performance lead it had over Intels competing processors for a significant...


This practice pushes components beyond their specifications and may cause erratic behaviour, overheating or premature failure. Even if the computer appears to run normally, problems may appear under heavy load. For example, during Windows Setup, you may receive a file copy error or experience other problems [6]. Most PCs purchased from retailers or manufacturers, such as Hewlett-Packard or Dell, do not allow the user to change the multiplier or Front Side Bus settings due to the probability of erratic behavior or failure. Motherboards purchased separately to build a custom machine are more likely to allow the user to edit the multiplier and FSB settings in the PC's BIOS. The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... This article is about the corporation Dell, Inc. ... For other uses, see Bios. ...


Pros and Cons

Pro

Although the front side bus architecture is an aging technology, it does have the advantage of high flexibility and low cost. There is no theoretical limit to the number of CPUs that can be placed on a FSB, though performance will not surely scale linearly across additional CPUs (due to the architecture's bandwidth bottleneck).


Con

The front side bus as it is traditionally known may be disappearing. Originally, this bus was a central connecting point for all system devices and the CPU. However, in recent years this has been breaking down with increasing use of individual point-to-point buses. The front side bus has recently been criticized by AMD as being an old and slow technology that bottlenecks today's computer systems. While a faster CPU can execute individual instructions faster, this is wasted if it can't fetch instructions and data as fast as it can execute them; when this happens, the CPU must wait for one or more clock cycles until the memory returns its value. Furthermore, a fast CPU can be delayed when it must access other devices attached to the FSB. Thus, a slow FSB can become a bottleneck that slows down a fast CPU.


See also

HyperTransport logo HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency point to point link that was introduced on April 2, 2001. ... The Intel QuickPath Interconnect or simply QuickPath [1][2] (formerly Common System Interface or CSI in short) is a point-to-point processor interconnect being developed by Intel, as a competitor to HyperTransport. ...

  Results from FactBites:
 
Front side bus - Wikipedia, the free encyclopedia (981 words)
This bus and the cache memory connected to it is faster than accessing the system RAM via the front side bus.
With bus speeds increasing rapidly, it is often necessary to run the RAM at a lower frequency than the system bus in order to stay within the limitations of the DRAM modules on the memory stick.
The front side bus as it is traditionally known may be disappearing.
What is FSB? Front Side Bus Info (373 words)
The front side bus on a computer connects the processor to the north side bridge, which comprises the memory bus, PCI bus and AGP bus.
For example, a processor running at 550MHz might be using a 100 MHz FSB; this means there is a clock multiplier setting of 5.5, thus the CPU is set to run at 5.5 times the MHz speed of the front side bus: basically equating to 100 MHz x 5.5 = 550 MHz.
Typically a FSB today is dual or quad channel, meaning a FSB speed advertised as being "333 MHz" may actually be 166 MHz dual channel, effectively meaning 333 MHz of speed.
  More results at FactBites »

 
 

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