The VAX was really a beautiful architecture and a good fit for systems that ran lots of small processes subsequently. However, it was also notoriously bad at ru

The VAX was really a beautiful architecture and a good fit for systems that ran lots of small processes subsequently. However, it was also notoriously bad at running LISP because of its huge page table overhead. A page was 512 bytes in size, giving an address space of 2^23 pages. So when a process grew larger, the machine started to swap out parts of the page table and everything went down to a crawl. This is probably what you observed. 512-byte pages worked fine on a 18-bit or 22-bit architectures, like the various models of the PDP-10 and the PDP-11, but were simply too small for the VAX. So the VAX did solve the memory shortage of its predecessors, but in the case of LISP at the price of abysmal performance when running memory-intensive applications, which many LISP programs unfortunately were.