[white-flame]

Many stack systems boast about the large number of operations they can perform per second. However, a stack "operation" is not equivalent to a register machine operation.

Something like "reg1 = reg2 + 125" is a single instruction in almost every register ABI, while at they very, very least, a stack machine would need two instructions: "push 125, add". If reg1 isn't immediately accessible as the stack head, and reg2 isn't consumed as the head, then you also need load/store/swap/roll/etc stuff wrapping the addition.

That's up to 6 (or even more) stack instructions to perform what a register machine can do in 1.

Also, when talking about interpreters, there is a not-insignificant overhead of fetching and dispatching the next instruction. That overhead is continually compounded when you need multiple instructions to perform what you could do in a single operation otherwise. The simpler the instructions are, the higher percentage of time is "wasted" performing instruction dispatch instead of carrying out core instruction processing. This can be parallelized in hardware instruction dispatch, but is pretty firmly stuck being serial in software interpreters.

Stack machines have very concise source code representations, and their individual instructions are simple and fast. But they can be very bloated in terms of the number of native instructions executed to carry out an overall program's work.

[vilda]

You seem to be confused with theoretical stack-based machines with their clear implementation, and their practical implementations. There's no reason why stack-based machine cannot have one instruction to add a constant, for example "addc 125" to add 125 to the top of the stack.

Similarly, there's no reason why register-based VMs wouldn't have push/pop instructions.