Information Technology Reference
In-Depth Information
First, conceptually, information is divided into three basic
types: instructions telling the computer what to do, general data
(normally integers without decimal points), and real (or floating
point) numbers with decimal points. As Figure 1.4 suggests, the
floatingpoint (FP) registers are the fullcapacity storage locations
for real numbers, and the generalpurpose (GP) registers hold
other data. The chip contains special circuitry associated with
each type of register to perform basic operations, such as addition
and multiplication. As the names suggest, a Floating Point Unit
contains the basic circuitry for such capabilities as arithmetic
operations and the comparison of floatingpoint numbers, while
the Integer Execution Unit performs the analogous functions for
integers and other data. Other, more specialized processing oper
ations are handled by circuits on the right side of the CPU chip,
including the Branch Processing Units, the Dispatch and
Completion Units, and the System Register Unit. (Unfortunately,
details of these specialized operations and Units are beyond the
scope of this text.)
The PowerPC CPU chip contains a small, but highspeed, cache
for both data and instructions. Movement of data is initiated by the
Load/Store Unit which determines what information will be needed
next. The Data and Instruction Memory Management Units deter
mine whether the desired information is already in cache. (The var
ious tag fields help in this determination.) If the needed information
is already located in cache, it can be obtained quickly and directly
from the appropriate location on the chip. If not, the Bus Interface
Unit can be used to interact with the bus and main memory.
The outside edge of the chip contains about 240 small rectangu
lar pieces. These serve as the locations to make electrical connec
tions with the chip. However, because the entire chip is well under a
halfinch square, making such connections directly would be a sig
nificant practical challenge. As a result, most chips are housed with
in a relatively large
chip casing
that connects the chip itself to wires
or pins that are of a manageable size. In the case of the PowerPC
603, a typical casing is shown in Figure 1.5a. The corresponding
casing for a Pentium CPU chip is shown in Figure 1.5b.
For each example, the casing secures connecting wires to the
actual chip in a fixed and workable configuration. The result still is
not huge (measuring only
3
4
inch or so on a side), but the wire con
