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Rev

The last half of your first paragraph has several falsehoods. Regarding that video, you are ignoring a salient detail, and trying to apply a special case to a generalized application, which in reality is not possible. The ROM in that video appears to be OPT EPROM, and the RAM is definitely SRAM. The IBM PC and its clones use DRAM. There were a few compatible mobos that did use SRAM, but eventually DRAM won the contest over SRAM for computer main memory. Bottom line is that the complications of initializing and using DRAM render the idea of an auxiliary circuit to copy "ROM to RAM" impractical.
– sawdust
Commented Feb 5 at 10:40
1

The OP didn't ask about the IBM PC architecture specifically (he also stated a "custom CPU"). He was more interested in the general idea, to get an understanding how the process could work. What I mentioned was a perfectly feasible approach even if the IBM PC didn't operate that way.
– Gábor
Commented Feb 5 at 10:49
The OP also did specify 8086 and BIOS. What computer architecture relies on a BIOS and uses an Intel uP? Microsoft borrowed that concept from CP/M. Other computer architectures don't bother with a BIOS because that's too restrictive. One more time: that video does not apply to any modern computer that uses DRAM. There is no "perfectly feasible approach". What you mentioned is totally irrelevant because since the IBM PC, practically every computer built (except perhaps supercomputers) uses DRAM rather than SRAM for main memory.
– sawdust
Commented Feb 5 at 11:15

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