Hardware Reference
In-Depth Information
uses a richer, fuller-featured instruction set, which has more complicated instructions. As
an example, say you wanted to instruct a robot to screw in a lightbulb. Using CISC in-
structions, you would say the following:
1.
Pick up the bulb.
2.
Insert it into the socket.
3.
Rotate clockwise until tight.
Using RISC instructions, you would say something more along the lines of the following:
1.
Lower hand.
2.
Grasp bulb.
3.
Raise hand.
4.
Insert bulb into socket.
5.
Rotate clockwise one turn.
6.
Is bulb tight? If not, repeat step 5.
7.
End.
Overall, many more RISC instructions are required to do the job because each instruction
issimpler(reduced)anddoesless.Theadvantageisthattherearefeweroverallcommands
therobot(orprocessor)hastodealwith,anditcanexecutetheindividualcommandsmore
quickly, and thus in many cases execute the complete task (or program) more quickly as
well. The debate goes on whether RISC or CISC is really better, but in reality there is no
such thing as a pure RISC or CISC chip—it is all just a matter of definition, and the lines
are somewhat arbitrary.
IntelandcompatibleprocessorshavegenerallybeenregardedasCISCchips,althoughthe
fifth- and later-generation versions have many RISC attributes and internally break down
CISC instructions into RISC versions.
MMX Technology
MMX technology was originally named for
multimedia extensions
, or
matrix math exten-
sions
, depending on whom you ask. Intel officially states that it is actually not an abbre-
viation and stands for nothing other than the letters MMX (not being an abbreviation was
apparentlyrequiredsothattheletterscouldbetrademarked);however,theinternalorigins
areprobablyoneofthepreceding.MMXtechnologywasintroducedinthelaterfifth-gen-
eration Pentium processors as a kind of add-on that improves video compression/decom-
pression, image manipulation, encryption, and I/O processing—all of which are used in a
variety of today's software.
