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A scalar processor is classified as a single instruction, single data processor in Flynn's taxonomy.The Intel 486 is an example of a scalar processor. It is to be contrasted with a vector processor where a single instruction operates simultaneously on multiple data items (and thus is referred to as a single instruction, multiple data processor). [2]
On first inspection these can be considered a form of vector processing because they operate on multiple (vectorized, explicit length) data sets, and borrow features from vector processors. However, by definition, the addition of SIMD cannot, by itself, qualify a processor as an actual vector processor, because SIMD is fixed-length, and vectors ...
Multiple autonomous processors simultaneously operating at least two independent programs. In HPC contexts, such systems often pick one node to be the "host" ("the explicit host/node programming model") or "manager" (the "Manager/Worker" strategy), which runs one program that farms out data to all the other nodes which all run a second program.
Here, c[i:i+3] represents the four array elements from c[i] to c[i+3] and the vector processor can perform four operations for a single vector instruction. Since the four vector operations complete in roughly the same time as one scalar instruction, the vector approach can run up to four times faster than the original code.
The simplest processors are scalar processors. Each instruction executed by a scalar processor typically manipulates one or two data items at a time. By contrast, each instruction executed by a vector processor operates simultaneously on many data items. An analogy is the difference between scalar and vector arithmetic. A superscalar processor ...
Vector processors, some SIMD ISAs (such as AVX2 and AVX-512) and GPUs in general make heavy use of predication, applying one bit of a conditional mask vector to the corresponding elements in the vector registers being processed, whereas scalar predication in scalar instruction sets only need the one predicate bit.
While scalar languages like C do not have native array programming elements as part of the language proper, this does not mean programs written in these languages never take advantage of the underlying techniques of vectorization (i.e., utilizing a CPU's vector-based instructions if it has them or by using multiple CPU cores).
A later processor that used vector processing is the Cell Processor used in the Playstation 3, which was developed by IBM in cooperation with Toshiba and Sony. It uses a number of SIMD processors (a NUMA architecture, each with independent local store and controlled by a general purpose CPU) and is geared towards the huge datasets required by ...