Tektronix 4108 terminal?

Hi, I recently got a Tektronix 4170 and terminal from ebay. The terminal is a 4108, which I can't find in the 1985 catalog that introduces the 4170. The next catalog I have is 1989 and that lists no 41xx products. The enclosure for the terminal is very similar to a 4105, except that the finish is black and not that green-gray that is on most Tektronix gear of the period. The 4105 has a small cover on the back where you can add ROM to the terminal to enhance its functions. In this 4108, there is a cover in a similar area of the case, but it covers a set of 4 expansion slots. In my terminal, two of the slots are occupied. One looks to be memory and the other looks to be control. Had the tektronix terminal "mainframe" evolved by this time to be a substrate into which processing and memory cards were inserted to round out the system? I haven't opened the monitor case to look at it in detail. -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>