SIMDs and MIMDs are the most important categories of computer systems for parallel computing in Flynn’s classification scheme. Due to their higher flexibility in allowing processors to execute independently and their ability to use off-the-shelf microprocessors, the MIMD systems are generally favored and considered to be more powerful. In comparison, the SIMD systems are considered outdated. However, we observe that many intrinsic weaknesses of the MIMD systems are not fully recognized until they are compared while solving realtime scheduling problems. The SIMD systems have inherent advantages that MIMDs lack. In this paper, we compare SIMDs and MIMDs in real-time scheduling, e.g., scheduling for air traffic control. Two abstract parallel computation models, the ASC and BSP models that represent SIMDs and MIMDs respectively, are used in our discussion and analysis. We argue that the common belief that MIMDs have greater power than SIMDs is false. Our research shows that SIMDs are not outdated, as they offer tractable solutions for problems considered intractable with MIMDs. Rather, SIMDs are more efficient and powerful in some important application fields. They deserve more attention and considerations than they currently receive.
The different versions of the original document can be found in: