􀂉 Address bus
􀂾 For a device (memory or I/O) to be
recognized by the CPU, it must be
assigned an address
􀂃 The address assigned to a given device must
be unique
􀂃 The CPU puts the address on the address bus,
and the decoding circuitry finds the device
􀂉 Data bus
􀂾 The CPU either gets data from the device
or sends data to it
􀂉 Control bus
􀂾 Provides read or write signals to the
device to indicate if the CPU is asking for
information or sending it information

INSIDE THE
COMPUTER
More about
Data Bus
􀂉 The more data buses available, the
better the CPU
􀂾 Think of data buses as highway lanes
􀂉 More data buses mean a more
expensive CPU and computer
􀂾 The average size of data buses in CPUs
varies between 8 and 64
􀂉 Data buses are bidirectional
􀂾 To receive or send data
􀂉 The processing power of a computer is
related to the size of its buses

INSIDE THE
COMPUTER
More about
Address Bus
􀂉 The more address buses available, the
larger the number of devices that can
be addressed
􀂉 The number of locations with which a
CPU can communicate is always equal
to 2x, where x is the address lines,
regardless of the size of the data bus
􀂾 ex. a CPU with 24 address lines and 16
data lines can provide a total of 224 or 16M
bytes of addressable memory
􀂾 Each location can have a maximum of 1
byte of data, since all general-purpose
CPUs are byte addressable
􀂉 The address bus is unidirectional

INSIDE THE
COMPUTER
CPU’s Relation
to RAM and
ROM
􀂉 For the CPU to process information,
the data must be stored in RAM or
ROM, which are referred to as primary
memory
􀂉 ROM provides information that is fixed
and permanent
􀂾 Tables or initialization program
􀂉 RAM stores information that is not
permanent and can change with time
􀂾 Various versions of OS and application
packages
􀂾 CPU gets information to be processed
􀂃 first form RAM (or ROM)
􀂃 if it is not there, then seeks it from a mass
storage device, called secondary memory, and
transfers the information to RAM