Which Dec Emulation is the MOST useful and Versatile?

[Jon Elson]

On 10/30/2017 06:18 AM, Eric Smith via cctalk wrote:
> 2. What IBM defined as emulation was use of extremely specialized
> hardware and/or microcode (specifically, not the machine's general-purpose
> microcode used for natively programming the host machine).
As far as I know, IBM's 360s did NOT have any special 
purpose hardware associated with their emulation packages.
The only thing special was that additional microcode cards 
were installed.  In the 360/30, these were Mylar cards with 
word lines on them, they were punched on a card punch to 
punch out the capacitor plates to make zeroes.
On the 360/40, they were Mylar "tapes" that were punched to 
cut traces to go through or bypass the sense transformers.
On 360/50 and 65, they were etched word line boards that had 
traces that weaved under the bit line capacitor plates.
So, these were all custom to fit the specific instruction 
set to be emulated.  But, as far as I know, they added no 
additional logic to the machine to support the emulation.  
In some cases, this made things fairly inefficient.  At 
least on the 360/30, when running 14xx emulation, there were 
many holes in memory, because they did not convert between 
decimal and binary addresses.  So, memory locations 0-9 were 
used, A-F were inaccessible, 10-19 were used, 1A-1F were 
skipped, and so on.  Some of this made I/O buffers kind of 
strange, as the I/O buffers had to be repacked between the 
real I/O devices and the emulator's buffers.

Jon