Editing I/O bound (section)

==I/O bound as an inherent problem in computing==
<!-- I/O in this case does not refer to "CPU-to-memory" but exclusively "CPU-to-peripheral"; the whole von Neumann bottleneck story therefore DOES NOT apply to "I/O bound" -->

The I/O bound state has been identified as a problem in computing almost since its inception. The [[Von Neumann architecture]], which is employed by many computing devices, this involves multiple possible solutions such as implementing a logically separate [[central processor unit]] which along with storing the instructions of the program also retrieves actual data usually from [[main memory]] and makes use of this more accessible data for working. When the process is terminated it writes back the results to the original storage (usually the [[main memory]])<!-- check Harvard Architecture for contrast. -->.

Since data must be moved between the CPU and memory along a [[Bus (computing)|bus]] which has a limited [[Bit rate|data transfer rate]], there exists a condition that is known as the [[Von Neumann bottleneck]]. Put simply, this means that the data [[Bandwidth (computing)|bandwidth]] between the CPU and memory tends to limit the overall speed of computation. In terms of the actual technology that makes up a computer, the Von Neumann Bottleneck predicts that it is easier to make the CPU perform calculations faster than it is to supply it with data at the necessary rate for this to be possible.

In recent history, the Von Neumann bottleneck has become more apparent. The design philosophy of modern computers is based upon a physically separate CPU and main memory. It is possible to make the CPU run at a high data transfer rate because data is moved between locations inside them across tiny distances. The physical separation between CPU and main memory, however, requires a data bus to move data across
comparatively long distances of centimetres or more. The problem of making this part of the system operate sufficiently fast to keep up with the CPU has been a great challenge to designers.<ref>[http://erikengbrecht.blogspot.com/2008/06/what-does-io-bound-really-mean.html Erik Engbrecht's Blog: What does I/O bound really mean?]</ref>