Hardware Reference
In-Depth Information
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 manufac-
turedandsoldtoday.TheZ80wasnotpincompatiblewiththe8080,butinsteadcombined
functionssuchasthememoryinterfaceandRAMrefreshcircuitry,whichenabledcheaper
andsimplersystemstobedesigned.TheZ80incorporatedasupersetof8080instructions,
meaning it could run all 8080 programs. It also included new instructions and new intern-
al 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 20MHz), contained 8,500 transistors, and could access 64KB of
memory.
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
andKaypromachines.Othercompaniesfollowed,andsoontheZ80wasthestandardpro-
cessor 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 8085became 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-Motorola engineers who had worked on Motorola's first processor, the 6800,
designed this chip. The 6502 was an 8-bit processor like the 8080, but it sold for around
$25, whereas the 8080 cost about $300 when it was introduced. The price appealed to
Steve Wozniak, who placed the chip in his Apple I and Apple ][/][+ designs. The chip
was also used in systems by Commodore and other system manufacturers. The 6502 and
its successors were used in game consoles, including the original Nintendo Entertainment
System (NES),amongothers.Motorola wentontocreate the68000series, whichbecame
thebasisfortheoriginallineofAppleMacintoshcomputers.Thesecond-generationMacs
used the PowerPC chip, also by Motorola and a successor to the 68000 series. Of course,
the current Macs have adopted PC architecture, using the same processors, chipsets, and
other components as PCs.
