Calculators: What's Inside

Display  Green, greeny-blue, blue and occasionally orange are Vacuum Fluorescent Display (VFD).  Red, with a magnifying lens displays are Light Emitting Diode (LED) Diodes  Usually small glass tubes with a wire each end.  A line usually identifies the cathode end.  These control the direction of current. CPU The central processing unit.  A small silicon chip with many hundreds of transistors encapsulated in a multi-legged case.  This integrated circuit is the "brain".   Capacitor  This particular type that looks like a blob is a tantalum bead capacitor.  Chosen for its accuracy and stability over temperatures.  Used to  set timing circuits.
On this side you can clearly see the 9V battery connector which also joins up to the adapter socket. 9V designs were usually required to drive early LEDs, 6V and 3V designs used lower voltages for later VFDs.

On this side of the image you can see the array of connecting wires that join to the keyboard printed circuit which is underneath this one.
The number of connections (and power required) to the display were reduced by multiplexing.  Only one digit of an LED array would be alight at any one time - hence the display flickered if moved quickly before your eyes. You may see more than one  integrated circuit - perhaps ones used to control the display or keyboard input.
The one pictured here is a 40-pin Dual-in-line configuration (DIL)
Resistors  Tubes with a wire each end.  Usually have several coloured bands to identify their value.  Resistors control the flow of current and drop voltages. Transistors  Plastic or metal cylinders with three legs.  Used to switch signals on and off and drive high current devices such as displays. Capacitor  This disc shaped capacitor is called a "ceramic disc" type.  Stable at high frequencies and very small. Capacitor  The square shaped ones are usually Mylar capacitors, useful for very large capacitors used to smooth power supplies.
date code Date Code If you're lucky you will see a date code for the integrated circuit manufacturing date.  This one reads 7252, week 52 of 1972. Display driver In this model the large array of transistors, resistors and diodes is used to drive the higher current to the display devices.  Later integrated circuits used less outside components as they could power the display directly.