Talk:Prime Computer/Archives/2013

Microcode from floppy
One of the most interesting things to me about Prime computers (at least ones that I worked with for a while) and the PRIMOS OS, was that the actual main CPU didn't boot immediately when the system was switched on; what you saw on the console terminal was the VCP, the Virtual Control Program (if memory serves me). The VCP was a small microprocessor-based computer-in-the-computer and it booted from a 5.25" floppy disk (at least on the 2550 and I think on the 9955) and was in charge of downloading the microcode from another floppy disk to the main CPU which was a two-board unit that contained many chips (I remember recognizing a bunch of Z80s on the main CPU board of the 2550) so not just one chip as we would expect from a CPU nowadays.

After the microcode was downloaded into the main CPU, the computer could boot from a tape or from harddisk; something that would take approximately 20 minutes on our systems. I wonder how many support calls they got from people who shut down their Prime for some reason and then discovered that they couldn't restart it because one of the floppy disks (which weren't used for any other purpose) were missing from the two full-size drives, or unreadable because the drives had gotten dusty. Anyway later on (at least in the 2350) they replaced the floppy disk drives by a small custom-made circuit board with EPROMs which was plugged into the back of the machine.

Jac Goudsmit 0:46, 05 June 2007 (UTC)


 * You do know why the floppy disk was invented, right? Guy Harris 22:47, 13 June 2007 (UTC)

More on Microcode on Floppy
The early Prime systems had the microcode in prom so these were "instant on" (to boot). The 750 (or 850 dual 750 processors) was the last to have the microcode in prom. In fact the microcode took up about one total board in the 5 board set, somewhere around 70-80 proms. It was thought (among us field techs) that it was changed to floppy to make it easier to change and less likely to mess up a microcode swap (70 16-pin dips to get in the right order and in properly). The 2250 "Rabbit" (first office environment Prime) had the dual 5 1/4" floppy VCP but the 2350 did have a little microcode "dongle". Larger systems after the 2350/2450 still used the dual floppy VCP up through the "600" line, such as 6550 systems. These floppy sets also contained the power on diags and extended diags to test the CPU set. Not always the best, but if you had a failure the diags would find it made life simplier. The real pain was the speed of the floppy transfers. We all knew how to load the code without the power on diags. Yes, there were times that the dirty floppies prevented the system from restarting after a PM (preventive maintence) but most of us had spares stashed away or other system locally to borrow from. The format of the floppy wasn't standard DOS but disk utils, that copied bit to bit, would allow you to make copies (I'm forgetting the names, perhaps PC Tools). —Preceding unsigned comment added by Vduber k (talk • contribs) 18:22, 29 April 2009 (UTC)

Microcode; also memory map
Loading the processor microcode from floppy was also charactoristic of the DEC VAX 11/780.

Another wierd thing - some of the bootup parameters required specific parts of the memory map to be "hard wired" - pieces of the map dedicated to some specific applications running on that particular machine. Don't remember much else, it's been a while. RobertTaylor21 21:06, 13 June 2007 (UTC)

Added Photo
Added photo of a real Prime 9950 with Console monitor. Taken in 1988. Took awhile to find this old photo.

--User: (talk • contribs • count) 00:16, 6 July 2007 (UTC)