Flynn’s classification is based on the nature of the instruction flow executed by the computer and that of the data flow on which the instructions operate.
SIMD with Shared Memory
SIMD without Shared Memory
In shared memory, there’s a high likelihood of memory conflict and hence reduces performance. The advantage is reduced cost because of the relatively simple circuitry required. Also because of the shared memory, data sharing processing units is faster.
In a system with dedicated memory, there’s the absence of memory conflict and performance is hence increased. The disadvantage is increased cost due to the complex circuitry needed.