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Introduction to Microprocessors
Notes Introduction
A microprocessor, sometimes called a logic chip, is a computer processor on a microchip.
The microprocessor contains all, or most of, the central processing unit (CPU) functions and is
the “engine” that goes into motion when you turn your computer on. A microprocessor is designed
to perform arithmetic and logic operations that make use of small number-holding areas called
registers. Typical microprocessor operations include adding, subtracting, comparing two numbers,
and fetching numbers from one area to another. These operations are the result of a set of
instructions that are part of the microprocessor design.
When your computer is turned on, the microprocessor gets the first instruction from the basic
input/output system (BIOS) that comes with the computer as part of its memory. After that,
either the BIOS, or the operating system that BIOS loads into computer memory, or an application
program is “driving” the microprocessor, giving it instructions to perform.
1.1 Microprocessor
Microprocessors are regarded as one of the most important devices in our everyday machines
called computers. Before we start, we need to understand what exactly microprocessors are and
their appropriate implementations. Microprocessor is an electronic circuit that functions as the
central processing unit (CPU) of a computer, providing computational control. Microprocessors
are also used in other advanced electronic systems, such as computer printers, automobiles, and
jet airliners. Typical microprocessors incorporate arithmetic and logic functional units as well as
the associated control logic, instruction processing circuitry, and a portion of the memory hierarchy.
Portions of the interface logic for the input/output (I/O) and memory subsystems may also be
infused, allowing cheaper overall systems. While many microprocessors have single chip designs,
some high-performance designs rely on a few chips to provide multiple functional units and
relatively large caches.
When combined with other integrated circuits that provide storage for data and programs, often
on a single semiconductor base to form a chip, the microprocessor becomes the heart of a small
computer, or microcomputer. Microprocessors are classified by the semiconductor technology of
their design (TTL, transistor-transistor logic; CMOS, complementary-metal-oxide semiconductor;
or ECL, emitter-coupled logic), by the width of the data format (4-bit, 8-bit, 16-bit, 32-bit, or 64-
bit) they process; and by their instruction set (CISC, complex-instruction-set computer, or RISC,
reduced instruction set computer: see RISC processor). TTL technology is most commonly used,
while CMOS is favoured for portable computers and other battery-powered devices because of
its low power consumption. ECL is used where the need for its greater speed offsets the fact that
Figure 1.1: Chips
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