Johnny wrote:
> Uh, the 11/780 and 11/785 is the same design.


There's only slightly more truth to that claim than there would be to
a claim that the 11/45 and 11/70 are the same design.

> Neither loaded the microcode from disk.


The 11/785 most certainly did.

The JCS (Joint Control Store) module (M7475) has 512x104 bits of PROM (13
512x8 PROMs) for control store, and 4Kx99 bits of RAM (99 2147 chips, 4Kx1
each). The microword is 96 bits plus 3 bits of parity. The PROM supplies
a "spare" bit, as well as 4 extra bits that are completely unused.

The PROM control store to help the machine boot; 512 words isn't enough
to make it a VAX. AFAIK once the real microcode is loaded, the PROM
control store isn't used.

> Heck, they only have one RX01 drive.


You're claiming that a 256 Kbyte RX01 floppy disk doesn't have
sufficient capacity to store 48 Kbytes of microcode?

> They might have had some patch ram in the same way as the 11/750. Not sure
> about that one...


The 11/780 does. The 11/785 doesn't need it, since the entire main
microcode store is RAM.

Eric
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