One of the cool things about spending a lot of time learning how to rebuild the Defender machine, is that you soon build up a fair amount of knowledge about how it works and the history behind it.

So I recently updated a post on KLOV with the correct information about the 3 different production versions of the Williams Defender ROM sets, and what is actually different about them (see below)

What is also interesting is that in the court case between Williams (maker of Defender) and Artic (maker of bootleg Defense Command) they reveal that the early ROM sets had a bug where the score for one of the Alien Symbols is incorrect

“The game created by the Artic circuit boards contains an error which was present in early versions of the Williams computer program – it displays the wrong score value for destroying a particular alien symbol”

That version is what is generally referred to as the “White” ROM label and was used on early trade and test machines – it’s probably also there in the Blue Label early version too (*to check!)

1. Defender Blue Label


Defender Blue Label has 10 EPROMs and has no EPROMs in position IC5 (as per normal Red ROMs) AND in position IC4

It shares the following ICs with Defender Green Label – IC2, IC6, IC7, IC8, IC9, IC10, IC11, IC12

IC1 and IC3 are different and are both 4k 2532s (their part numbers are 5343-09595-00 and 5343-09597-00) 

2. Defender Green Label

Defender Green Label has 11 EPROMs and no EPROM in position IC5

It shares the following ICs with Defender Blue Label – IC2, IC6, IC7, IC8, IC9, IC10, IC11, IC12

IC1, IC3 and IC4 are different with IC1 and IC4 being 2k 2716 EPROMs and IC3 being a 4k 2532 EPROM

3. Defender Red Label

Defender Red Label has 11 EPROMs and no EPROM in position IC5

No EPROMs appear to be shared with earlier sets (all part numbers are different)

All ICs are 2k 2716s EXCEPT IC2 and IC3 which are 4k 2532 EPROMs

I’ll put up a scan of both part tables on my www.thedefenderproject.com site for reference and hope this helps other people out

The ROM boards also have differing jumpering which I will document there too – hope that helps!