Right... The PDT-130 and -150 both used the same device driver (PD), though they would display as different device codes, if I remember. The interesting thing about them was the fact that the firmware knew about RT-11 queue elements, so all the driver had to do was take the queue element and pass it to the ROM, which handled the IO, returning if there was an error, or when the request was satisfied. The driver then returned to the monitor the completed queue element. The PDTs were also interesting in that they used an 8085 (later an 8085A) to handle the IO page. Word accesses were about 90ms, byte accesses were about 180ms if I remember correctly, and we had to avoid any read-modify-write instructions (BIS/BIC) otherwise it would take twice as long as the 90ms/180ms... Finally, an interesting point, the PDT-11/110, which had no storage devices, had code in ROM which understood the same protocol as the GT40 for downloading code... Somewhere I have a program I wrote for use at a science fiction convention (worldcon-1980, in boston) where I used a PDT-11/150 to download a GT40 with various programs like lunar lander or roses, or bowling, etc... (The favorite, of course, was lunar lander) Megan Gentry Former RT-11 Developer +--------------------------------+-------------------------------------+ | Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry!zk3.dec.com | | Unix Support Engineering Group | (home): mbg!world.std.com | | Compaq Computer Corporation | addresses need '@' in place of '!' | | 110 Spitbrook Rd. ZK03-2/T43 | URL: http://world.std.com/~mbg/ | | Nashua, NH 03062 | "pdp-11 programmer - some assembler | | (603) 884 1055 | required." - mbg | +--------------------------------+-------------------------------------+