The Card card is quite literally the ‘beating heart’ of the computer and without it nothing would work.
Although a single card it’s actually made up of two different clocks that can be selected. One is a more ’traditional’ relay based clock but has a fixed speed. The other is crystal oscillator based and the frequency can be changed from 0.25Hz through to 32Hz.
Below is a list of the blog articles relating to this card (in reverse date order):