Page 39 - A Practical Guide from Design Planning to Manufacturing

The Evolution of the Microprocessor 15

but a jumble of many small crystals called polycrystalline silicon,
polysilicon, or just poly. By forming polysilicon gates before adding dopants,
the gate itself would determine where the dopants would enter the
silicon crystal. The result was a self-aligned MOSFET. The resistance
of polysilicon is much higher than a metal conductor, but with heavy
doping it is low enough to be useful. MOSFETs are still made with poly
gates today.
The computers of the 1960s stored their data and instructions in
“core” memory. These memories were constructed of grids of wires with
metal donuts threaded onto each intersection point. By applying current
to one vertical and one horizontal wire a specific donut or “core” could
be magnetized in one direction or the other to store a single bit of infor-
mation. Core memory was reliable but difficult to assemble and oper-
ated slowly compared to the transistors performing computations. A
memory made out of transistors was possible but would require thou-
sands of transistors to provide enough storage to be useful. Assembling
this by hand wasn’t practical, but the transistors and connections needed
would be a simple pattern repeated many times, making semiconductor
memory a perfect market for the early integrated circuit business.
In 1968, Bob Noyce and Gordon Moore left Fairchild Semiconductor
to start their own company focused on building products from inte-
®
grated circuits. They named their company Intel (from INTegrated
ELectronics). In 1969, Intel began shipping the first commercial inte-
grated circuit using MOSFETs, a 256-bit memory chip called the 1101.
The 1101 memory chip did not sell well, but Intel was able to rapidly
shrink the size of the new silicon gate MOSFETs and add more tran-
sistors to their designs. One year later Intel offered the 1103 with 1024
bits of memory, and this rapidly became a standard component in the
computers of the day.
Although focused on memory chips, Intel received a contract to design
a set of chips for a desktop calculator to be built by the Japanese com-
pany Busicom. At that time, calculators were either mechanical or used
hard-wired logic circuits to do the required calculations. Ted Hoff was
asked to design the chips for the calculator and came to the conclusion
that creating a general purpose processing chip that would read instruc-
tions from a memory chip could reduce the number of logic chips
required. Stan Mazor detailed how the chips would work together and
after much convincing Busicom agreed to accept Intel’s design. There
would be four chips altogether: one chip controlling input and output
functions, a memory chip to hold data, another to hold instructions,
and a central processing unit that would eventually become the world’s
first microprocessor.
The computer processors that powered the mainframe computers of the
day were assembled from thousands of discrete transistors and logic chips.