Datasheet

30 Chapter 1
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Hardware
Instruction Set The motherboard’s chipset contains an instruction set for communicating
with the CPU; the CPU must understand the commands in that set. For example, a mother-
board designed for an AMD Athlon CPU can’t accept an Intel Pentium CPU, because the
instruction set is different.
Voltage The CPU requires that a certain voltage of power be supplied to it via the mother-
board’s interface. This can be anywhere from +5V for a very old CPU down to around
+2.1V for a modern one. The wrong voltage can ruin the CPU. One reason a given mother-
board can’t support many different CPUs is that it must provide the correct voltage. To get
around this issue, some motherboards have voltage regulator modules (VRMs) that are
able to change the voltage based on the CPU.
There are several ways of differentiating one CPU from another. The following sections
explain specifications according to type, speed, voltage, and cache memory.
CPU Speed
The CPU’s speed is the frequency at which it executes instructions. This frequency is
measured in millions of cycles per second, or megahertz (MHz); or billions of cycles per
second, or gigahertz (GHz).
The CPU has an internal and an external speed. The external speed corresponds with the
motherboard’s speed, based on its system crystal. The system crystal pulses, generating a
cadence at which operations occur on the motherboard. Each pulse is called a clock tick. The
CPU’s internal speed is usually a multiple of that, so that multiple operations occur internally
per clock tick. A CPU’s speed as described in its specifications is its internal speed.
CPU Manufacturers
The market leader in the manufacture of chips is Intel Corporation, with Advanced Micro
Devices (AMD) gaining market share in the home PC market. Other competitors include
Motorola and IBM.
INTEL PROCESSORS
The first commercially successful Intel CPU was the 8086, developed in the late 1970s. It
was used in the IBM XT, one of the early home and business personal computers. Other
early Intel CPUs included the 80286, 80386, and 80486. You may find it useful to learn
about the specifications of these CPUs for your own knowledge, but they aren’t covered
on the current A+ exam.
PENTIUM
Intel introduced the Pentium processor in 1993. This processor has 3.1 million transistors
using a 64-bit data path, a 32-bit address bus, and a 16KB on-chip cache, and it comes in
speeds from 60MHz to 200MHz. With the release of the Pentium chips, dual pipelining was
introduced (also called superscalar architecture), allowing the chip to process two operations
at once.
The term Pentium refers to three separate CPUs: first-generation, second-generation, and
MMX. First-generation Pentiums were 273-pin PGA CPUs (Socket 4) drawing +5V. They
ran at 60MHz or 66MHz. The second-generation Pentiums were 296-pin models (Socket
5 or Socket 7) drawing +3.3V. They ran at between 75Mhz and 200MHz.
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