Originally, a programmer would have been able to use all of the computer's
memory (if possible, the area with the loader program was left alone so that the
loader code wouldn't have to be toggled into memory again). The requirements of
the new peripheral devices made it advantageous to reserve a part of memory for
"systems code" – the specialized code that controlled the new devices. The new
organization for main memory is shown in Figure 3.1; part of memory is reserved
for the "system's code" (and, also, for system's data – the system needed memory
space to record information such as identifiers associated with magnetic tapes on different tape decks).
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