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External Data Bus / Address Bus

Discussion in 'A+' started by Stuzzle, Oct 29, 2008.

  1. Stuzzle

    Stuzzle Byte Poster

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    Hi guys,

    I've never asked for help here yet, so this'll be where I find out if the replies here are helpful answers to questions or screams to look on Google before posting like in other forums I've seen

    Basically I'm reading the Mike Meyers A+ AIO, currently on processors and earlier I quickly browsed through the end of chapter questions, and they ended up confusing me in regards to External Data and Address bus

    See, I thought that the External Data bus was responsible for all data in and out of the CPU, whereas the Address Bus spoke to the MCC about what RAM it wishes to access

    But the answers to the end of chapter questions seemed to state otherwise. I can't give exact quote right now what with been at work, but could someone clear this up for me please just what specifically each does :oops:
     
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  2. Stuka

    Stuka Nibble Poster

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    Stuzzle, I could be wrong here, as its been a while since I looked over CPU's/RAM, but to my knowledge the Address bus is used when an application needs something from memory, i.e it will say to the memory control chip, "I want to print data" - the mcc will look in RAM and find the data in hexadecimal "storage" areas in RAM, then present the data it to the application via the data bus.

    As for the CPU's external bus, well, I think its just the system bus/FSB, isn't it? Data going to the cpu from the northbridge to be processed.

    I could be wrong, even I'm confused now and I must've read about it a dozen times when I was studying that part of the book, lol.
     
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  3. Dullage

    Dullage Byte Poster

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    Stuzzle, my advice would be to carry on reading an come back to that chapter later. I struggled to get my head around it at first but a lot became clear after reading a few chapters after.

    Good Luck :D
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    You are basically correct about the buses. I've looked at the questions and answers and don't see where they imply anything different.

    All data flows through the data bus. Just *where* it flows to/from is controlled by the address bus.

    Harry.
     
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  5. dmarsh

    dmarsh Terabyte Poster

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    The address bus determines the memory location to read, the data bus transfers the data.

    Both buses are parallel buses, the width of the bus determines how many locations can be uniquely identified in the case of the address bus. A 34 bit bus is 2 power 32 or 4 gigabytes, a 64 bit bus is 2 power 64 or 18.45 exabytes.

    The data bus and address buses can be of different widths.

    The width of the data bus determines how much data can be moved in one cycle of that bus, 32 bit bus can move 32 bits per cycle etc.

    from :- http://www.pcguide.com/ref/ram/timingBus-c.html
     
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  6. Mp4

    Mp4 Bit Poster

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    From : http://www.webopedia.com/

    i know its a copy , but maybe it might clear some things up for you


    External Data Bus

    A bus that connects a computer to peripheral devices. Two examples are the Universal Serial Bus (USB) and IEEE 1394.

    Contrast with internal data bus. The bit width of internal and external data buses are not always equal.

    Address Bus

    A collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed. Modern PCs and Macintoshes have as many as 36 address lines, which enables them theoretically to access 64 GB (gigabytes) of main memory. However, the actually amount of memory that can be accessed is usually much less than this theoretical limit due to chipset and motherboard limitations
     
  7. Stuzzle

    Stuzzle Byte Poster

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    :biggrin Thanks for the response everyone!
    Will just keep on going and see if it "clicks" into place at a later point
     
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  8. Roy2005

    Roy2005 New Member

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    does the external bus also control data from a pci card ( not PCIe) are PCI cards class as peripherals
     
  9. greenbrucelee
    Highly Decorated Member Award

    greenbrucelee Zettabyte Poster

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    Yes, see the explanation given above.
     
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  10. dmarsh

    dmarsh Terabyte Poster

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    There are multiple external buses, it would depend on which one you meant, the buses are often controlled by bus controllers. The PCI bus controller would control the transmission of data from PCI cards. The buses can often be interconected with bridges.

    For external Buses...Goto Control Panel > System > Device Manager
    Select View Devices by Connection.

    You should see things like :-
    PCI Bus
    PCI Bridge
    USB Hub / Controller
    Serial ATA Controller
    SCSI/RAID Host Controller
     
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  11. Roy2005

    Roy2005 New Member

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    Can someone tell me if i am understanding thsi correctley, A PCIe card runs a peer to peer with the device does this mean that this does not touch the external bus

    sorry to be so dimm just starting to get into Motherboards and CPU ect ,,,,,
     
  12. dmarsh

    dmarsh Terabyte Poster

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    From here :-

    http://en.wikipedia.org/wiki/PCI_Express

    Basically its a switched serial network not a bus in the standard sense of parallel data bus.
     
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  13. Roy2005

    Roy2005 New Member

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    thanks for that made life so much easer
     
  14. supernova

    supernova Gigabyte Poster

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    I expect future memory standards will go the same way
     
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  15. dmarsh

    dmarsh Terabyte Poster

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    "The Network is the Computer" - John Gage

    Its become true in so many different ways...
     
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