1 illustrates the term of register transfer level (RTL). Principally,
each digital information processing system consists of memory
means (flip-flops, registers, memory cells) and combinational
networks. Its function is determined completely by the memory
means RG and by the Boolean equations that describe the combinational
networks CN. In the following, the resources can therefore
be illustrated by simple register transfer level (RTL) diagrams.
RTL diagrams and Boolean equations that describe the functional
units of conventional computers can be found in numerous textbooks,
hardware manuals and the like.
1 Principal illustration of the register transfer
level (RTL). RG = memory means (registers), CN = combinational
2 shows register transfer level diagrams of simple resources,
comprising registers and combinational networks. For example,
elementary resources (fig. 1.6a) generate a single result (X)
from two operators (A, B):
:= A OP B or X := OP (A, b)
of the processing instructions of typical general-purpose computers
correspond to this scheme (the differences lie primarily in
the way how the operands are delivered and how the result is
assigned). The well-known arithmetic logic units (ALUs) can
be viewed as examples of such elementary resources.
computers know only a few elementary data types, for example,
integers, floating point numbers, characters, strings and so
on. The operation unit usually processes only data of
some particular types (for example, integers or floating point
numbers). In case of elementary operations, the operands
and the results have the same format.
resources have no such limitations. A resource can create
from an arbitrary number of operands any number of results,
wherein the operands and the results may belong to any data
type or data format (fig. 2b, c). There is also no limitation
to elementary data types. The data types can be as complex
as desired (bit and character strings, arrays, heterogeneous
structures (records) and the like).
2 Some basic resources.
typical general-purpose computer executes one instruction at
a time. Hence a single processing resource is sufficient. It
is self-evident to increase the performance by providing several
processing resources. Fig. 3 shows two examples. When
the resources are independent (fig. 3a), utmost flexibility
is ensured. However, there remains the problem of supplying
them with operands (parameters) and to remove the results. Fig.
3b illustrates one solution: The resources are to be connected
according to the most frequent data flow, so that the results
can immediately become operands of other resources (concatenation).
3 Independent (a) and concatenated (b) resources.
4 illustrates an alternative configuration. The
resources are connected to a random access memory (RAM). Program
execution is to be divided into sequences of three steps:
operands are loaded into the resources.
operands are processed within the resources (simultaneously
in all of them).
results are brought back into the memory.
4 Independent resources attached to a random
access memory (RAM).
5 illustrates that the resources can be implemented with hardware
as well as with software. Memory areas with memory cells for
the parameters and the results (fig. 5b) correspond to the operand
and result registers of the hardware (fig. 5a); programs that
carry out the respective information processing operations (fig.
5c) correspond to the combinational networks. Another alternative
is to store the description of a circuitry that can perform
the respective information processing operations (fig. 5d).
Such descriptions can be, for example, provided as net
lists or as Boolean equations. Based on this, it is possible
to generate the respective hardware (for example, on a programmable
integrated circuit) or to emulate its function (functional hardware
5 Two resources (OP1, OP2) implemented in different