Which Dec Emulation is the MOST useful and Versatile?

Kip, I think "emulation" and "simulation" get used pretty much interchangeable. SIMH is touted a simulator, Hercules/390 as an emulator yet they are both programs that provide a "bare metal" machine via software on which an operating system can be installed. Neither make any attempt to reproduce the speed of the original CPU. I am going to stick with "emulator" as I think of "simulation" as process whereby we can model some statistical or mathematical parameters e.g. how long the queues are in a supermarket, what time is high tide in Boston using only mathematics. Note this may involve a general purpose computer, or it may use specialist machines such as the Doodson-Lege Tidal Predictor http://www.ntslf.org/about-tides/doodson-machine So to return to emulating other computers have at least five different flavours... 1. Functional Software Emulation where we match the functions but not the speed of operation using a program. SIMH and Hercules are such beasts For much work this is fine. Most software emulators take this approach. 2. Cycle accurate Software Emulation/Simulation where we attempt to match both function and speed of the underlying hardware. This may be necessary for software which uses software loops to control say the speed of a UART. I If you want to use the simulator for historical research this may help. Some emulators can be switched to this mode when software needs it... David Sharp's SSEM/Baby simulator is such a beast. http://www.davidsharp.com/baby/ 3. Behavioural Hardware Emulation This is where we build a hardware implementation of a machine, but do not attempt to duplicate the exact detail of the logic or its speed of operation. Richard Stofer's IBM1130 in VHDL is such a project. He doesn't have it available on the Web (I have a copy and have run it) There is a Flash video on the IBM1130.org site 4. Cycle Accurate Behavioural Hardware Emulation This is probably the most common approach to cycle accurate emulations. Because FPGA's typically run several times faster than the clock on legacy hardware, and they may contain high level function blocks, e.g. multipliers its often "relatively easy" to match the instruction times of a legacy CPU in an FPGA. My BabyBaby FPGA implementation of the SSEM FPGA is such a beast. It runs at the same speed as replica SSEM in MSI Manchester but internally it's a parallel implementation whereas the real Baby is a serial machine. https://hackaday.com/2016/01/06/babybaby-a-1948-computer-on-an-fpga/ 5. Gate Level Hardware Emulation It gate level hardware emulation we try and re-implement the hardware down to the logic gate level. This is hard because FPGA's are may not be designed to work this way, and gate level design will also have some dependencies on propagation delays, which on an FPGA will be much smaller than on any real hardware. A couple of examples of these are Laurence Wilkinson's IBM 360/30 http://www.ljw.me.uk/ibm360/ Carl Claunch's IBM 1130 http://ibm1130.blogspot.co.uk/ I hope this doesn't muddy the water too much... Dave confused. this <cctalk at classiccmp.org> a configurable