Hardware Reference
In-Depth Information
In April 1972, Intel released the 8008 processor, which originally ran at a clock speed of 500KHz
(0.5MHz). The 8008 processor contained 3,500 transistors and was built on the same 10-micron
process as the previous processor. The big change in the 8008 was that it had an 8-bit data bus, which
meant it could move data 8 bits at a time—twice as much as the previous chip. It could also address
more memory, up to 16KB. This chip was primarily used in dumb terminals and general-purpose
calculators.
The next chip in the lineup was the 8080, introduced in April 1974. The 8080 was conceived by
Frederico Faggin and designed by Masatoshi Shima (former Busicom engineer) under Faggin's
supervision. Running at a clock rate of 2MHz, the 8080 processor had 10 times the performance of
the 8008. The 8080 chip contained 6,000 transistors and was built on a 6-micron process. Similar to
the previous chip, the 8080 had an 8-bit data bus, so it could transfer 8 bits of data at a time. The
8080 could address up to 64KB of memory, which was significantly more than the previous chip.
The 8080 helped start the PC revolution because it was the processor chip used in what is generally
regarded as the first personal computer, the Altair 8800. The CP/M operating system (OS) was
written for the 8080 chip, and the newly founded Microsoft delivered its first product: Microsoft
BASIC for the Altair. These initial tools provided the foundation for a revolution in software because
thousands of programs were written to run on this platform.
In fact, the 8080 became so popular that it was cloned. Wanting to focus on processors, Frederico
Faggin left Intel in 1974 to found Zilog and create a “Super-80” chip, a high-performance, 8080-
compatible processor. Masatoshi Shima joined Zilog in April 1975 to help design what became
known as the Z80 CPU. The Z80 was released in July 1976 and became one of the most successful
processors in history. In fact, it is still being manufactured and sold today.
The Z80 was not pin compatible with the 8080, but combined functions such as the memory interface
and RAM refresh circuitry, which enabled cheaper and simpler systems to be designed. The Z80
incorporated a superset of 8080 instructions, meaning it could run all 8080 programs. It also included
new instructions and new internal registers; therefore, whereas 8080 software would run on the Z80,
software designed for the Z80 would not necessarily run on the older 8080. The Z80 ran initially at
2MHz (later versions ran up to 25MHz), contained 8,500 transistors, and could access 64KB of
memory. The Z80 is still used in products such as scientific and graphing calculators and has been
developed into faster versions with larger memory addressing space by Zilog and many other
vendors. Descendents of the Z80 are currently used in audio processing chips, telecom, and
peripheral controllers.
RadioShack selected the Z80 for the TRS-80 Model 1, its first PC. The chip also was the first to be
used by many pioneering personal computer systems, including the Osborne and Kaypro machines.
Other companies followed, and soon the Z80 was the standard processor for systems running the
CP/M OS and the popular software of the day.
Intel released the 8085, its follow-up to the 8080, in March 1976. The 8085 ran at 5MHz and
contained 6,500 transistors. It was built on a 3-micron process and incorporated an 8-bit data bus.
Even though it predated the Z80 by several months, it never achieved the popularity of the Z80 in
personal computer systems. It was, however, used in the IBM System/23 Datamaster, which was the
immediate predecessor to the original PC at IBM. The 8085 became most popular as an embedded
controller, finding use in scales and other computerized equipment.
Along different architectural lines, MOS Technologies introduced the 6502 in 1976. Several ex-