Here is a small synthetical post on hardware resources of a system microprocessor.

* The processor (CPU) is the heart of the system. It’s like a bandmaster,  he make the calculations, take decisions in terms of addressing and allocation of resources within the system.
* The ROM (read only memory) is the persistence support data such as database, LDAP, filesystem, etc … Access to such data is expensive, we must limit it
* The RAM (memory) is volatile memory. Access is very fast and can therefore « hide » the information for which we need quick access. This resource is limited and as we shall see, it can rapidly be saturated with mismanagement.
* Ports (I / O): is access to peripherals and network. Acquisitions connections are expensive, so they should be limited.

These system components are connected by 3 bus:

* The data bus allows, as its name suggests, the movement of data, but also instructions to the 4 blocks.
* The address bus allows the processor to show every time the memory cell or device which he wants to appeal.
* The control bus is also operated by the processor and indicates, for example, if one wants to write or read in a memory cell, or an entry / exit to or from a device, also found in the bus control one or several lines that allow peripheral circuitry to make requests to the processor, these lines are called hardware interrupts (IRQ).

We shall see in the next sections how these resources are requested in an application and give us some ideas to optimize.