Wire Wrap Technolog used on the PDP-8

Wirewrap is an technology to interconnect electronics that was popular in the 1960's to 1980's. It uses wire which is wrapped around pins to make electrical connections. The advantages of wirewrap is that it can be used to wire large assemblies, easily modifiable, and easy to create prototype systems. This technology was used on the original PDP-8, the PDP-8/I and many of the peripherals for the backplane interconnect between the cards. The backplane size on these machines was larger than feasable to make with a single PC board but the small cards plugged into these machines were easy to create with etched PC boards. With these early PDP-8's most of the options were pre wired into the backplane but some connections were rewired in the field if options are installed to enable them. Engineering change orders (ECO's) were also installed by rewiring parts of the backplane to fix errors that were found in the design. Later machines such as the PDP-8/E used a PC board backplane where all slots were the same.

The wirewrap technology declined in use because the PC board technology costs dropped and allowed higher density. Wirewrap was labor intensive even with the semi-automated wirewrap machines. Also PC boards allowed for a more controlled signal enviornment which was required for faster logic.

The older equipment like the DF32 disk drives used larger rectangular pins of about .030 x .060 inches and 24 gauge wire. The newer machines such as the PDP-8/I used .025 inch square pins and 30 gauge wire.

More wirewrap information  And here

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