ZiLOG Z80 Handbook page 5

Preface
Microprocessors have evolved from units that handled data in
4-bit slices with rudimentary instruction sets into devices that rival,
or surpass, minicomputers in architecture and software instruction
repertoire. The Zilog Model Z-80 represents a microprocessor that is
extremely sophisticated from both a hardware implementation and
software implementation viewpoint. The Z-80 microprocessor is
truly a computer on a chip that requires only a few external compo-
nents-a 5-volt power supply, a simple oscillator, and read-only
memory-to construct a complete computer system. The instruction
set of the Z-80 includes that of the Intel 8080A as a subset, making
the Z-80 an ideal software replacement for the 8080A; the Z-80 has
many new instructions and addressing modes to supplement the
8080A instructions. A search of a string of characters, for example,
can be implemented with one instruction after initialization, the one
search instruction replacing four equivalent instructions in other
microprocessors.
In addition to the Z-80 microprocessor itself, Zilog has imple-
mented other devices to supplement the power of the Z-80. A PIO
provides parallel I/O with two 8-bit ports, software configured I/O,
vectored-interrupt capability, and automatic priority interrupt en-
coding. A CTC, or Counter-Timer-Circuit, provides programmable
counting and timing functions for real-time events. Other major
devices are also available. Zilog and other manufacturers have de-
veloped microcomputer systems based on this family of Z-80 devices,
and the systems have played their role in narrowing the gap between
"minicomputer systems" and "microcomputer systems," a division
that becomes less and less distinct from month to month.
The purpose of this book is threefold, to acquaint the reader with
the hardware of the Z-80, to discuss the almost overwhelming (in
number of instructions) software aspects of the Z-80, and to describe
microcomputer systems built around the Z-80.