A Comparison of Two Microprogrammable Processors: PDP-11/40E and MLP-900

This document, dated May 1975, evaluates two microprogrammable processors: the MLP-900 (a 36-bit machine at the Information Sciences Institute) and the PDP-11/40E (a modified 16-bit machine at Carnegie-Mellon University). The author compares their performance across four benchmark programs—a 64-bit integer multiply (MMPY), a character translation routine (TRANS), a memory allocation routine (ALLOC), and a NOVA minicomputer emulator (NOVA)—along with evaluating architectural differences, branch costs, and ease of programming. The findings indicate that while the MLP-900 excels in data-path heavy tasks (like multi-word integer multiplication), the PDP-11/40E generally performs better on byte-handling and standard emulation tasks. The paper concludes with insights into how architectural strengths and programming challenges impact the suitability of each machine for specific applications.