On 10/30/2017 2:42 PM, Chuck Guzis via cctalk wrote:
Well, "emulate" is a very fuzzy word, even in the context that you provide. Taking as an example, some pre-S/360 hardware that's easily verified, is the IBM 7094. It ran the instruction set of the 7090 but with a single departure--the use of 7 index registers, selectable using a 3-bit isntruction field. In the 7090, that same field selected any of three registers--if you selected more than one, the contents were ORed together before subtracting from the base address. The 7094 did have a "7090 compatibility mode" that used only the first three index registers in the same manner as the 7090. Specific hardware than enabled one machine to act as another. So, is that "7090 emulation" on a 7094? --Chuck
In the sense that the 7094 can emulate (regular English usage) a 7090, then yes it is.
- J.
