On 28 Jul 2004 at 13:55, Jay West wrote: My comment was addressed specifically to your "FFP option 100" statement, not the ROM numbers. The "FFP option 100" adds the DMS ROMs to the FFP ROMs. I'm going to go way out on a limb here, as I am far more familiar with the M-series than the E-series, but in looking over the ROM history, it appears that prior to the consolidation, FFP took six 1K ROMs (1 module) and three 4K ROMs (2 modules) on the Firmware Accessory Board (FAB). DMS took six 1K ROMs (1 module) on the FAB too. The FAB had only twelve 1K ROM sockets, so a system with FFP and DMS would fully populate the FAB's 1K area. Six 1K ROMs provided one microcode module (256 words), and three 4K ROMs provided two modules. Given that FFP and DMS together comprised four modules, it appears that they were consolidated into six 4K ROMs. The FAB had eighteen 4K sockets, so by consolidating the ROMs, much of the FAB space was freed for user microprograms. Prior to the consolidation, FFP used 1K ROMs 13306-80013 through 80018 (one module) and 4K ROMs 5090-0589 through 0591 (two modules). DMS used 1K ROMs 13307-80027 through 80032 (one module). After the consolidation, the original FFP 4K ROMs were used, and a new set of three 4K ROMs (13307-80033 through 80035) were added. This latter set combined the two single modules So in other words, when you ordered DMS by itself, you received three 4K ROMs that contained the single DMS module plus one of the three FFP modules. The latter was useless without the other two FFP modules, of course. When you ordered FFP by itself, you received three 4K ROMs that contained two of the three FFP modules. If you already had the three 4K DMS ROMs installed in your machine from an earlier purchase, then the third FFP module would already be present, and your combined FFP/DMS setup would work. But if you didn't have DMS, then you'd be missing the third FFP module, and that's what "FFP option 100" added. Because of the consolidation, it also added the DMS microcode, but presumably without the Memory Expansion Module (MEM) board that was part of the DMS package, the DMS microcode wouldn't do you any good, so it came along relatively "free." No, it's 13306B, because the extra ROMs are needed when FFP is ordered for a machine that doesn't have the 4K DMS ROMs installed, so it's an FFP option. In the "A" versions of those products, it was...up until the ROM consolidation. That may have been the point when A became B -- an earlier ordering guide from August 1978 lists only the 1K + 4K ROM set for the 13306A FFP and only the 1K ROM set for the 13307A. No, sorry, as noted in my first comment, I was addressing just the ordering option, not the ROM numbers. 13306 ROMs are (part of) FFP. I hazard the guess that the consolidation was done to free up 1K space on the FAB for user microprograms, and also because the later-introduced and preferred Firmware Expansion Module (FEM) card took only 4K and 8K ROMs. I trust that it's all clear now. ;-) -- Dave