Comment by adrian_b

The main influencer of the 8087 architecture, William Kahan, had previously worked on the firmware of the HP scientific calculators, so he was well experienced in implementing numeric algorithms by using stacks.

When writing in assembly language, the stack architecture is very convenient and it minimizes the program size. That is why most virtual machines used for implementing interpreters for programming languages have been stack-based.

The only real disadvantage of the stack architecture is that it prevents the concurrent execution of operations, because all operations have a resource dependency by sharing the stack as output location.

At the time when 8087 was designed, the possibility of implementing parallel execution of instructions in hardware was still very far in the future, so this disadvantage was dismissed.

Replacing the stack by individually addressable registers is not the only possible method for enabling concurrent execution of instructions. There are 2 alternatives that can continue to use a stack architecture.

One can have multiple operand stacks and each instruction must contain a stack number. Then the compiler assigns each chain of dependent operations to one stack and the CPU can execute in parallel as many independent chains of dependent instructions as there are stacks.

The other variant is to also have multiple operand stacks but to have the same instruction set with only one implicit stack, while implementing simultaneous multi-threading (SMT). Then each hardware thread uses its own stack while sharing the parallel execution units and then one can execute in parallel as many instructions as there are threads. For this variant one would need to have much more threads than in a CPU with registers, which combines superscalar execution with SMT, so one would need 8 or more SMT threads to be competitive.