What is it● A Bus is a system that moves data from one source to another● First implementation was in early computing with a System bus
Why is it needed● The purpose of buses is to reduce the number of "pathways" needed for communication between the components, by carrying out all communications over a single data channel. This is why the metaphor of a "data highway" is sometimes used.● Synchronization between components● HIGH speed transfer between CPU/CPU/MEMORY
CharacteristicsWe measure data transfer by two metrics: 1. Total number of bits we can transfer inparallel. This is called the width of the data. 2. The clock rate or frequency (in Hertz) ofthe busEach time data is sent or received isconsidered one cycle
Total Transfer Speed: BandwidthA bus with a width of 16 bits and a frequencyof 133 MHz, therefore, has a transfer speedequal to:● 16 * 133.106 = 2128*106 bit/s,● or 2128*106/8 = 266*106 bytes/s● or 266*106 /1000 = 266*103 KB/s● or 259.7*103 /1000 = 266 MB/s
BUS Timeline● 1982 - ISA by IBM - 4.77 MB/s (8 bits wide at 4.77 MHz)● 1988 - Standard Architecture (EISA) - 33.32 MB/s (32 bits at 8 MHz)● Early 90s - PCI Peripheral Component Interconnect - 133MB/s (32-bit at 33 MHz)● Mid 90s - USB 1.0 1.5 MB/sec● 2000 - USB 2.0 60 MB/sec● 2010 - USB 3.0 500 MB/sec● 2011 - PCI Express 3.0: 31.5 GB/s
Usually two main buses in a PCThe internal bus(sometimes calledthe front-side bus orFSB for short or thesystem bus).The expansion bus(sometimes calledthe input/output busor the control bus)
Front Side Bus or System Bus● A Standard CPU system bus is comprised of a Control bus, an Address bus and a Data bus.● The FSB can range from speeds of 66 MHz, 133 MHz, 100 MHz, 266 MHz, 400 MHz, and up.● Most CPU today add a third bus known as an Expansion bus.
Expansion Bus● Used to add additional expansion cards into the CPU.● Comes in Internal and External● Common internal buses are PCI, PCI express and SATA● Common external buses are USB, CAN and IEEE 1394(Firewire)
Chipsets● The Northbridge is an integrated circuit (e. g.,Intel orVIA) that is responsible for communications between the CPU interface,AGP,PCI, and the memory. The Northbridge gets its name for commonly being North of the PCI bus.● The Southbridge is responsible for the hard- drive controller, I/O controller and integrated hardware such as sound card, video card if present on the motherboard, USB, and Ethernet.
How it Works an overviewWhen the CPU needs datafrom RAM, a request is sent tothe Northbridge memorycontroller. After the requesthas been received, itresponds with how long theprocessor will need to wait inorder to read the memoryover the front side bus(FSB).Some newer motherboardshave replaced the
Multipliers● In computing a multiplier, CPU multiplier, clock ratio, clock multiplier, CPU Core Ratio is the speed ratio between the CPU and the FSB.● For example, a CPU with a multiplier of 20 and an external clock of 133 MHz will have a CPU speed of 2.66GHz.● Memory often has a multiplier to it which some BIOS let you tweak for different performance.
Overclocking● CPU speed is generally calculated by a bus speed (often called the FSB) and a multiplier.● Multiply these together and you get the actual speed the CPU runs at. The bus speed is typically the speed that other components (such as the memory) in a system run at.● You overclock your CPU by increasing one or the other or both. Bus speed tends to have the best effect so if possible people will
Overclocking (continued)Even though the CPU is at the same speed the computerwill be MUCH faster with a 200MHz bus then with a100MHz bus. This is because the bus is what carriers thedata to and from the CPU, the faster you make the busthe less of a bottleneck it becomes. The CPU no longerhas to wait as long for the next instruction.Just make sure to have better cooling, and you need tohave more voltage going to the components (CPU andchipsets)
PCI Express Why its so fastEach lane of a PCI Expressconnection contains two pairs ofwires -- one to send and one toreceive. Packets of data moveacross the lane at a rate of one bitper cycle. A x1 connection, thesmallest PCIe connection, has onelane made up of four wires. Itcarries one bit per cycle in eachdirection. A x2 link contains eightwires and transmits two bits atonce, a x4 link transmits four bits,and so on. Other configurations arex12, x16 and x32.
PCI Express How it works● Prioritization of data, which allows the system to move the most important data first and helps prevent bottlenecks● Time-dependent (real-time) data transfers● Better handshaking and error detection● Each device has its own dedicated, point-to-point connection to the switch, signals from multiple sources no longer have to work their way through the same bus.
Referenceshttp://www.d-silence.com/feature.php?id=237http://en.kioskea.net/contents/pc/bus.php3http://arstechnica.com/features/2004/07/pcie/http://old.pinouts.ru/Slots/http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-the-PCI-Express/190/3http://www.waste.org/~winkles/hardware/pci.htmhttp://dangerousprototypes.com/docs/Bus_Piratehttp://www.cpushack.com/cpu-overclocking.htmlTyson, Jeff, and Ed Grabianowski. "How PCI Works" 02 May 2001. HowStuffWorks.com. <http://computer.howstuffworks.com/pci.htm> 02 December 2012.Null, Linda, and Julia Lobur. The Essentials of Computer Organization and Architecture. Sudbury, MA: Jones andBartlett, 2006. Print.Lucas, S.E. (2008). The Art of Public Speaking (10th ed.). McGraw-Hill: New York.Street, N.J. (2009). Packet for Public Speaking: Comm. 203, Spring 2009.
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