Information Technology Reference
In-Depth Information
the machine cycle by following predetermined internal instructions, known as
microcode
.
You can think of microcode as predefined, elementary circuits and logical operations that
the processor performs when it executes an instruction. The control unit executes the
microcode in accordance with the electronic cycle, or pulses of the CPU “clock.” Each
microcode instruction takes at least the same amount of time as the interval between
pulses. The shorter the interval between pulses, the faster each microcode instruction can be
executed.
Because the number of microcode instructions needed to execute a single program
instruction—such as performing a calculation or printing results—can vary, the clock speed
is not directly related to the true processing speed of the computer.
Clock speed is often measured in
megahertz
(MHz, millions of cycles per second) or
gigahertz
(GHz, billions of cycles per second). One of the earliest microprocessors was
the Intel 8080 with a clock speed of only 2 MHz. This microprocessor was used in the first
IBM PC circa 1982. Twenty years later, the Pentium 4 processor had a clock speed of
3.2 GHz—1,600 times faster. Unfortunately, the faster the clock speed of the CPU, the more
heat that is generated. This heat must be dissipated to avoid corruption of the data and
instructions the computer is trying to process. Also, chips that run at higher temperatures
need bigger heat sinks, fans, and other components to eliminate the excess heat. This increases
the size of the computer, a problem for manufacturers of portable devices.
The excess heat created by a fast CPU can also be a safety issue. In the summer of 2006,
Dell and Apple Computer, in conjunction with the U.S. Consumer Product Safety Com-
mission, announced large recalls of laptop computer batteries. Additional recalls of batteries
in Toshiba and Lenovo laptop computers followed. Under certain circumstances, these bat-
a battery-related fire broke out in the overhead bin of a JetBlue Airways flight. In March
2007, a battery overheated or ignited on an American Airlines aircraft. In both cases, fast-
acting flight attendants quickly extinguished the fire and avoided disaster. In response to
these accidents, some airlines now require that laptop users remove the computer's battery
when plugged into the aircraft's power supply. Other airlines are asking passengers to be sure
all loose batteries are stored in insulated bags or otherwise capped to prevent being shorted.
Chip and computer manufacturers are exploring various means to avoid heat problems
in their new designs. Demand-based switching is a power management technology developed
by Intel that varies the clock speed of the CPU so that it runs at the minimum speed necessary
to allow optimum performance of the required operations. IBM and Hewlett-Packard (HP)
are also experimenting with direct jet impingement, a technique that deploys an array of tiny
nozzles and a distributed return architecture (spray water on, funnel it off) to spray cooling
water on the back of the processor.
Manufacturers of portable electronic devices such as computers and cell phones are also
seeking more effective sources of energy as portable devices grow increasingly power hungry.
A number of companies are exploring the substitution of fuel cells for lithium ion batteries
to provide additional, longer-lasting power. Fuel cells generate electricity by consuming fuel
(often methanol) while traditional batteries store electricity and release it through a chemical
reaction. A spent fuel cell is replenished in moments by simply refilling its reservoir or by
replacing the spent fuel cartridge with a fresh one. The use of micro fuel cells based on volatile
alcohol will be limited until regulatory restrictions against transporting them on aircraft
are lifted.
Cell Broadband Engine Architecture (or simply Cell) is a microprocessor architecture
that provides power-efficient, cost-effective, and high-performance processing for a wide
range of applications. The Cell is an example of innovation across multiple organizations. A
team from IBM Research joined forces with teams from IBM Systems Technology Group,
Sony, and Toshiba to provide a breakthrough in performance for consumer applications.
The Cell can be used as a component in high-definition displays, recording equipment, and
computer entertainment systems. The first commercial application of the Cell was in the
Sony PlayStation 3 game console, where it performs at the rate of 2 trillion calculations per
second. Toshiba plans to incorporate Cell in high-definition (HD) TV sets. IBM plans to
use Cell processors as add-on cards to enhance the performance of the IBM System z9
mainframe computers.
4
microcode
Predefined, elementary circuits and
logical operations that the proces-
sor performs when it executes an
instruction.
megahertz (MHz)
Millions of cycles per second.
gigahertz (GHz)
Billions of cycles per second.
