The front panel has two rows of 18 DISPLAY lights but the IBM 1800's used a 16-bit register display so I am not sure if the lights correspond with memory. The first row is labeled A - DISPLAY, the second B - DISPLAY. The 18 toggle switches under the 2 rows of lights are "three way switches; ON / NULL / OFF. Click image for larger view.
Below the two sets of 18 DISPLAY lights on the left side is another set of 10 lights and toggle switches labeled C - DISPLAY. Click image for larger view.
To the right of the C - DISPLAY controls is a pair of black strips which I had hoped was used for some kind of numeric readout, but upon closer inspection I learned that it's just paint. The two lights are labeled SAMPLE INTLK and DISPLAY HOLD. Click image for larger view.
The bottom right of the control panel is used for various control switches including a section for display SET CONTROL, HOLD CONTROL, and RESET. There is also a PROBE INPUT and a COMPARE EXIT jack. Click image for larger view.
On the bottom right the controls pertain to SIGNAL LINES TO DEVICE ADAPTERS. Click image for larger view.
Removing the rear cover reveals a set of Solid Logic Technology (SLT) chips and a few connectors. Click image for larger view.
Here is a close up of the SLT chips installed in the back-plane. SLT / flip chips were common during the 60's and most computers used some sort of flip chip set. A few have been removed to reveal the connector pins. Click image for larger view.
A close up of an IBM Solid Logic Technology (SLT) controller. Click image for larger view.
IBM Machine History initiated when the item went into service in October 1969.