Single-core processors like the 486, Pentium, Pentium2 and Pentium4 had processes and threads, and many many programmers found them useful in the 1980s and 1990s.

Multicore computers weren't popular until the mid 00s, long after processes and threads were implemented in modern OSes.

------------

That is, for the entire time in the 1980s and 1990s, on single-core processors... processes and threads would _NOT_ speed up your programs (as per #1), because you only had a singular core. Task switching doesn't help at all on a 486 or a Pentium in terms of #1.

But task switching / threads helps in terms of Hard Drives (elevator algorithm), networking, and other I/O issues.

Even today: OSes like FreeRTOS offer you threads and/or processes on single-core systems like STM32G0 and other small microcontrollers.

----------

Windows 95 was when multiprocessing became popular in the Microsoft world. It would take another decade before typical home users had multicores. 99% of the time, a program sat there, waiting for the mouse to move or some other event to happen.