[jan-jaap]

If you piece together history based on magazine articles and announcements, then the 4D/60 was showed first at the March '87 NCGA conference and exhibition. In July they were shipping to customers, but that same month the turbo upgrade for 4D/60 owners (4D/60T) was announced. This single board computer with the new 12.5MHz CPU is better known as the IP4. In October '87 they started shipping the 4D/70 which came from factory with the IP4. In April '88, the price-reduced 4D/50 was announced.

The initial price for a 4D/60 was $74500. The price for the turbo upgrade was $7500. When the 4D/70 started shipping, the price was again $74900 and the price of the 4D/60 was simply dropped by $7500. The initial price for a 4D/50 was $49900.

If you add all of this up, if gives a good idea of your chances of finding an unmolested 4D/60. First of all, it was only a couple of months between initial shipment and the arrival of the IP4 so they probably went to select customers. The opportunity to get a 2 .. 3x speed improvement for an extra 10% was probably irresistible for 4D/60 owners. I doubt many 4D/60s were sold once the 4D/70 started shipping, and the arrival of the 4D/50 surely was the end of the 4D/60.

So a time window of a couple of months, select (government?) customers and an irresistible upgrade. You do the math

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The metal chassis of this 4D/50 'G' has a sicker on it that says "SBC CHASSIS REV H, DATE 5/25/88", so it was probably delivered to customer in Q3 '88.