Casio AS-A, AS-C, AS-L

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These three desktop calculators show the progress in semiconductor technology at the end of the 1960ies.
The very primitive AS-A, it has for example no decimal point key, is built with two printed circuit boards with a total area of 153cm². They contain 34 integrated circuits with mostly 14 or 16 pins.
The AS-C needs the same PCB-area, but by using higher integrated circuits it is significantly more powerful. One can see 14 small ICs an four 36- pin ICs made by Fairchild on the lower PCB.
The AS-L needs only a PCB-area of 84 cm² and has an architecture which can be seen as a kind of microprocessor with the exception, that the CPU is still not integrated on one single chip.
Its program memory consists of 2*256 words with 8 bits, from which all except of one are really used. Data memory on all three calculators are PMOS-shift registers, data processing is bit-serial.

AS-A and AS-C use older high-treshold-technology from Hitachi (HD 31.. with -24 volt supply), the AS-L uses a newer low-lhreshold-technology (HD 32.. with -14 volt).