Hardware Reference
In-Depth Information
The data bus and address bus are independent, and chip designers can use whatever size
they want for each. Usually, however, chips with larger data buses have larger address
buses. The sizes of the buses can provide important information about a chip's rel-
ative power, measured in two important ways. The size of the data bus indicates the
chip's information-moving capability, and the size of the address bus tells you how much
memory the chip can handle.
Internal Registers (Internal Data Bus)
The size of the internal registers indicates how much information the processor can op-
erate on at one time and how it moves data around internally within the chip. This is
sometimes also referred to as the
internal data bus
. A
register
is a holding cell within the
processor; for example, the processor can add numbers in two different registers, storing
the result in a third register. The register size determines the size of data on which the
processor can operate. The register size also describes the type of software or commands
and instructions a chip can run. That is, processors with 32-bit internal registers can run
32-bit instructions that are processing 32-bit chunks of data, but processors with 16-bit
registers can't. Processors from the 386 to the Pentium 4 use 32-bit internal registers and
can run essentially the same 32-bit OSs and software. The Core 2, Athlon 64, and new-
er processors have both 32-bit and 64-bit internal registers, which can run existing 32-bit
OSs and applications as well as newer 64-bit versions.
Processor Modes
All Intel and Intel-compatible processors from the 386 on up can run in several modes.
Processor modes refer to the various operating environments and affect the instructions
andcapabilitiesofthechip.Theprocessormodecontrolshowtheprocessorseesandman-
ages the system memory and the tasks that use it.
