Please use the form below to search our dictionaries by entering a word you wish to define. (If you search this site to define words regularly, support this FREE site - Donate! )

Define the word bus master

bus master
     
         The device in a computer which is driving the
        address bus and bus control signals at some point in time.
        In a simple architecture only the (single) CPU can be bus
        master but this means that all communications between
        ("slave") I/O devices must involve the CPU.  More
        sophisticated architectures allow other capable devices (or
        multiple CPUs) to take turns at controling the bus.  This
        allows, for example, a network controller card to access a
        disk controller directly while the CPU performs other tasks
        which do not require the bus, e.g. fetching code from its
        cache.
     
        Note that any device can drive data onto the data bus when
        the CPU reads from that device, but only the bus master drives
        the address bus and control signals.
     
        Direct Memory Access is a simple form of bus mastering where
        the I/O device is set up by the CPU to read from or write to
        one or more contiguous blocks of memory and then signal to the
        CPU when it has done so.  Full bus mastering (or "First Party
        DMA", "bus mastering DMA") implies that the I/O device is
        capable of performing more complex sequences of operations
        without CPU intervention (e.g. servicing a complete NFS
        request).  This will normally mean that the I/O device
        contains its own processor or microcontroller.
     
        See also distributed kernel.
     
        (1996-08-26)