An Overview of Software Component Value

Delay and delay variability and the ability to multitask are key elements of software
component value. The job of an operating system is to sit between the software resident
in the device and the device hardware (see Figure 8.1). Going back in history, an
operating system such as Microsoft DOS (Disk Operating System) reads physical
memory (hardware) in order to open a file (to be processed by software). In a PDA or
3G wireless handset, the operating systems to date have typically been ROM-based
products. This is changing, however, because of the need to support remote reconfigurability
and dynamic application downloads.

Applications are sometimes described as embedded or even deeply embedded. The
more deeply embedded the application, the more remote it is from the outside world.
In other words, the more deeply embedded the application, the more deterministic it
becomes—that is, it performs predictably. As the application is moved closer to the real
world, it has to become more flexible, and as a result, it becomes less predictable in
terms of its overall behavior.
An example of embedded software is the driver software for multiple hardware
elements—memory, printers, and LCDs. There are a number of well-defined repetitive
tasks to be performed that can be performed within very closely defined time
scales. Moving closer to the user exposes the software to unpredictable events such as
keystroke interrupts, sudden unpredictable changes in the traffic mix, and sudden
changes in prioritization.