Editing Superscalar processor (section)

==Alternatives==
Collectively, these limits drive investigation into alternative architectural changes such as [[very long instruction word]] (VLIW), [[explicitly parallel instruction computing]] (EPIC), [[simultaneous multithreading]] (SMT), and [[Multi-core (computing)|multi-core computing]].

With VLIW, the burdensome task of dependency checking by [[hardware logic]] at run time is removed and delegated to the [[compiler]]. [[Explicitly parallel instruction computing]] (EPIC) is like VLIW with extra cache prefetching instructions.

Simultaneous multithreading (SMT) is a technique for improving the overall efficiency of superscalar processors. SMT permits multiple independent threads of execution to better utilize the resources provided by modern processor architectures. The fact that they are independent means that we know that the instruction of one thread can be executed out of order and/or in parallel with the instruction of a different one. Also, one independent thread will not produce a pipeline bubble in the code stream of a different one, for example, due to a branch. 

Superscalar processors differ from [[multi-core processor]]s in that the several execution units are not entire processors. A single processor is composed of finer-grained execution units such as the [[Arithmetic logic unit|ALU]], [[Integer (computer science)|integer]] [[Binary multiplier|multiplier]], integer shifter, [[Floating-point unit|FPU]], etc. There may be multiple versions of each execution unit to enable the execution of many instructions in parallel. This differs from a multi-core processor that concurrently processes instructions from ''multiple'' threads, one thread per [[Central processing unit|processing unit]] (called "core"). It also differs from a [[instruction pipelining|pipelined processor]], where the multiple instructions can concurrently be in various stages of execution, [[Assembly line|assembly-line]] fashion.

The various alternative techniques are not mutually exclusive—they can be (and frequently are) combined in a single processor. Thus a multicore CPU is possible where each core is an independent processor containing multiple parallel pipelines, each pipeline being superscalar. Some processors also include [[vector processor|vector]] capability.