The first pocket calculators became available around 1970, and within a decade, dozens of companies started selling simple calculators that anyone could afford. Many of these calculators used the same basic design, based on just a handful of different chipsets. General Instruments made the C-683, which is used in the calculator shown below.

This calculator (typical mid to late 1970's) was made by Audiosonic, a cheap brand that was sold in department stores. The display is made of LEDs, because LCDs were still too new and expensive for cheap consumer items like this. Unfortunately, LEDs are quite power-hungry, so this calculator will drain a 9V battery in about 8 hours. Long enough to be useable, but nothing compared to modern pocket calculators that will run for years on a single button cell.

A look at the circuit board. Note that the characters on the LED screen are very small and therefore have little magnifying lenses in front of them. The big chip is what makes this calculator tick: GI's C-683. This one was made in 1976.

And this is what we find inside. Typical 1970's IC technology, because we can see the individual interconnect wires even at the lowest level of magnification. There are probably about a thousand transistors in total. The block on the lower right is the memory that holds the numbers used in calculations. The rectangular area on the lower left is the ROM that contains the calculator's program. Most of it is taken up by the translation table to convert between the binary numbers in memory and the display segments that need to be turned on. The rest of the circuit performs the calculations and handles the input and output systems.

A closer look at the ROM area. It consists of a simple matrix of horizontal and vertical wires. If they are connected (by a dot), then that memory bit contains a "1", otherwise it's a "0".

The memory consists of a grid of transistors. They can be accessed through the vertical and (non-visible) horizontal wires running through them. The wires attached to the left of the memory seem to suggest that it's divided into three blocks. This would make sense, because the calculator needs to store three numbers: two inputs and one output.

On the lower right corner we find some information about the manufacturing process. The numbers "1" through "5" indicate the different masks ("layers") used in the process. The square thing to the left of it is probably a test circuit, like a single diode or resistor that can be measured by placing probes on the pads next to it.