Computer Machines: Applying the Stored Program Concept
Machine Instructions
To apply the stored-program concept, central processing unit (CPUs) are designed to recognize instructions encoded as bit patterns. This collection of instructions along with the encoding system is called the machine language. An instruction expressed in this language is called a machine-level instruction or, more commonly, a machine instruction.
The list of machine instructions that a typical CPU must be able to decode and execute is quite short. In fact, once a machine can perform certain elementary but well-chosen tasks, adding more features do not increase the machine’s theoretical capabilities. In other words, at a certain point, additional features may increase such things as convenience but add nothing to the machine’s fundamental capabilities. The degree to which machine designs should take advantage of this fact has lead two philosophies of CPU architecture.
One is that a CPU should be designed to execute a minimal set of machine instructions. This approach leads to what is called a reduced instruction set computer (RISC). The argument in favor of RISC architecture is that such a machine is efficient, fast, and less expensive to manufacture. On the other hand, others argue in favor of CPUs with the ability to execute a large number of complex instructions, even though many of them are technically redundant. The result of this approach is known as a complex instruction set computer (CISC). The argument in favor of CISC architecture is that the more complex CPU can better cope with the ever increasing complexities of today’s software. With CISC, programs can exploit a powerful rich set of instructions, many of which would require a multi-instruction sequence in a RISC design.
In the 1990s and into the millennia, commercially available CISC and RISC processors were actively competing for dominance in desktop computing. Intel processors, used in PCs, are examples of CISC architecture; PowerPC processors (developed by an
To apply the stored-program concept, central processing unit (CPUs) are designed to recognize instructions encoded as bit patterns. This collection of instructions along with the encoding system is called the machine language. An instruction expressed in this language is called a machine-level instruction or, more commonly, a machine instruction.
The list of machine instructions that a typical CPU must be able to decode and execute is quite short. In fact, once a machine can perform certain elementary but well-chosen tasks, adding more features do not increase the machine’s theoretical capabilities. In other words, at a certain point, additional features may increase such things as convenience but add nothing to the machine’s fundamental capabilities. The degree to which machine designs should take advantage of this fact has lead two philosophies of CPU architecture.
One is that a CPU should be designed to execute a minimal set of machine instructions. This approach leads to what is called a reduced instruction set computer (RISC). The argument in favor of RISC architecture is that such a machine is efficient, fast, and less expensive to manufacture. On the other hand, others argue in favor of CPUs with the ability to execute a large number of complex instructions, even though many of them are technically redundant. The result of this approach is known as a complex instruction set computer (CISC). The argument in favor of CISC architecture is that the more complex CPU can better cope with the ever increasing complexities of today’s software. With CISC, programs can exploit a powerful rich set of instructions, many of which would require a multi-instruction sequence in a RISC design.
In the 1990s and into the millennia, commercially available CISC and RISC processors were actively competing for dominance in desktop computing. Intel processors, used in PCs, are examples of CISC architecture; PowerPC processors (developed by an