Slight correction there on the 4D, in fact it was the longest-lasting of all the Model 4s (and III and I). My sources here are 80micro and old RS catalogs, but it was designed and premiered in late 1985 (80micro Oct 1985, p.21) and was sold through 1986 RS computer catalogs all the way until 1990 computer catalog. Basically 4-5 years depending on how you look at it. That's not to say they manufactured it for 4 years, the probably manufactured it for 2 years and it took the remaining time to sell off the inventory. I believe it was still available for purchase (though not in the catalog) during 1991, but can't remember where I heard that one (most likely CN80 or Frank Durda IV). For its latter life (1987 - 1991) I think the 4D was selling at a rate of about 80 units/month (from another obscure source I can't remember, maybe one of the final issues of 80micro).
By contrast the Gate array M4 was on the market for 1 year (mid 84-mid 85), the non-gate M4 for 1 year (mid-83 to mid-84), the M3 was on the market for 2.5 years (mid-81 until end of 83), and the M1 on the market for 3 years (mid-77 to mid-80).
Ian.
