of Microprocessors

150 MUSICAL ApPLICATIONS OF MICROPROCESSORS
desired. The operating system may either load the object file into memory
itself or a loader program may be used for that purpose. After loading, the
user may specify the data files, if any, and execute the program. With such a
setup, program size is limited only by the capacity of the diskette and the
amount of memory available for the assembler's symbol table. Most of the
preceding comments also apply to compiler languages such as FORTRAN or
the new structured microcomputer languages such as C and Pascal.
High-Level Language
By far the most popular high-level language for microcomputers is
BASIC. Originally developed at Dartmouth University for student use on a
large time-sharing computer, it has evolved well beyond its design goals into
a general-purpose programming language. Although its strengths and weaknesses
in music programming will be detailed in Chapter 18, it can be said
here that it is an excellent one-shot problem-solving language but not especially
suited for large or complex programs. As a matter of fact, most of the
waveforms and plots in this book were done using simple BASIC programs.
BASIC will also be used periodically to illustrate program algorithms. One
unique feature present in nearly all microcomputer BASIC is the PEEK and
POKE functions. These allow a BASIC program to directly address and read
or write any memory location in the microcomputer. If the system utilizes
memory-mapped 1/0 2 , then BASIC programs may be written to operate any
I/O device on the system!
On microcomputers, BASIC is almost exclusively implemented as an
interpreter and is permanently stored in read-only memory. Thus, BASIC
programs exist in memory as character strings in the same form as they
appear in print except for perhaps the substitution of single, normally
unprintable, bytes for keywords. Part of the BASIC interpreter is a simple,
line-number-oriented text editor. When the "run" command is given, the
interpreter scans each program line, extracts the meaningful information
from the line, acts upon it, and then goes to the next line. As a result, BASIC
programs tend to run very slowly compared to the inherent capability of the
microcomputer. Nevertheless, BASIC is very easy to learn and use and for any
but highly repetitive calculations its speed is adequate. Most disk-based
microcomputers also have a BASIC compiler available, which greatly speeds up
execution at the expense of losing the interpreter's interactive program
development feature.
Another commonly used language on microcomputers is simply called
C. It was developed at Bell Laboratories to run on PDP-ll minicomputers
and has efficiency features that make it suitable fot system programming as
2Memory-mapped I/O is peculiar ro the PDP-II line of minicomputers and most
microprocessors. Essentially all I/O device status, control, and data registers are
addressed like memory locations with all memory reference microprocessor instructions
available for I/O register manipulation.