Consequences in Machine Architecture
Use of a PC that normally increments assumes that what a computer does is execute a usually linear sequence of instructions. Such a PC (or equivalent hardware that serves the same purpose) is central to the von Neumann architecture. Thus programmers write a sequential control flow even for algorithms that do not have to be sequential. The resulting “von Neumann bottleneck” led to research into parallel computing, including non-von Neumann or dataflow models that did not use a PC; for example, rather than specifying sequential steps, the high-level programmer might specify desired function and the low-level programmer might specify this using combinatory logic.
This research also led to ways to making conventional, PC-based, CPUs run faster, including:
- Pipelining, in which different hardware in the CPU executes different phases of multiple instructions simultaneously.
- The very long instruction word (VLIW) architecture, where a single instruction can achieve multiple effects.
- Techniques to predict out-of-order execution and prepare subsequent instructions for execution outside the regular sequence.
Read more about this topic: Program Counter
Famous quotes containing the words consequences, machine and/or architecture:
“Cultivate the habit of thinking ahead, and of anticipating the necessary and immediate consequences of all your actions.... Likewise in your pleasures, ask yourself what such and such an amusement leads to, as it is essential to have an objective in everything you do. Any pastime that contributes nothing to bodily strength or to mental alertness is a totally ridiculous, not to say, idiotic, pleasure.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“He is no more than the chief officer of the people, appointed by the laws, and circumscribed with definite powers, to assist in working the great machine of government erected for their use, and consequently subject to their superintendence.”
—Thomas Jefferson (1743–1826)
“Defaced ruins of architecture and statuary, like the wrinkles of decrepitude of a once beautiful woman, only make one regret that one did not see them when they were enchanting.”
—Horace Walpole (1717–1797)