1.1 Analogy: Piano Architecture

1.1 Analogy: Piano Architecture

Architecture applies to buildings , landscapes , computers, and even pianos. Let us briefly consider the architecture of pianos. Piano architecture can be defined by the specification of the keyboard, as shown in Figure 1-1a. The keyboard is the player ( user ) interface to this musical instrument. It consists of 88 keys: 36 black keys and 52 white keys. Striking a key causes a note of specified frequency to sound. As the size and the arrangement of the keys are identical for all modern piano keyboards, anyone who can play the piano can play any piano.

Many implementations of piano architecture are possible, as shown in Figure 1-1b. The implementation is concerned with the details of a particular maker's materials. The kinds of wood and metal used, the selection of ivory or plastic keys, and the size and shape of the instrument are all implementation decisions made by the piano builder. Regardless of the implementation decisions made, however, any piano player can play the final product.

Table 1-1. Generations of Computer Languages

In a computer system, the architecture consists of the programming interface: the instruction set, the structure and addressing of memory, the control of input and output (I/O), and so on. Several implementations of an architecture can be possible using different electronic design techniques that may have different size, cost, and performance characteristics. A program that runs on one machine should run on all machines conforming to the same architecture. Indeed, computer architects including Rau and Fisher of Hewlett-Packard have expressed that a contract exists between programs written for the architecture and the processor implementations of that architecture.

1.2 Types of Computer Languages

The earliest computers had to be programmed by people who knew the detailed capabilities and limitations of the hardware. Memory was an especially precious resource, and great care and ingenuity were required to squeeze algorithms into the extremely limited space available. Subsequently, as the overall capabilities of computers improved and use became widespread, successive generations of computer languages were devised in order to improve programmer productivity and accuracy at the expense of performance and resources. Table 1-1 shows the progression of programming languages, where n GL means n th generation language.

Assembly language lies between machine language and higher-level languages, such as C or Pascal. Assembly language more precisely expresses the constraints of an architecture than do high-level programming languages, but the latter are more amenable to reuse of code segments and global optimization. Accordingly, learning at least one assembly language can lead to an appreciation of what high-level languages actually do behind the scenes.