Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

11.7 THE JAVA ETHOS – A TALE OF TWO PARTS

Let's remind ourselves of how a computer works. Computers have more or less stuck to an architectural theme that was popularised by the PC (what we used to call the IBM-compatible PC).

Figure 11.15 shows the basic computer architecture that revolves around the central processing unit (CPU), like a Pentium or Power PC, which can crunch numbers loaded from memory and output results back to memory across a bunch of printed-circuit wires called a bus²². Certain memory locations are special because they also enable the CPU to interface with peripherals, like a graphical display. Writing certain values to the display memory will affect what appears on each pixel on the screen and so in this way a software program can write a whole sequence of pixel values in order to control what the screen display. The operating system (OS) is a program that runs on the CPU and can run utility code to manage how this area of memory gets updated and in doing so also provide a more meaningful interface, like a windowing one, to other programs running on the CPU. These applications, instead of writing to the display memory, will write values to a portion of memory monitored by the window-utility part of the OS, which in turn writes to the display memory in a way that manages a windowed look-and-feel.

Figure 11.15 Basic computer architecture.

For the CPU to know ...