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Table 1.4 Orthogonal properties. Orthogonal instruction sets define all operations for all data types (all "x"s, below).

Operations

Half-word
IntegerShort

Word
IntegerLong

Double-word
Floating-point

Add

Subtract

Multiply

Divide

Shift right

Shift left

AND

NOT



		The default precision of a machine is typically one natural word in size. A natural word is the word size that a machine uses as its normal word size. For example, the IBM S/390 series has a natural word size of 32 bits and older entries in the Intel x86 series have a natural word size of 16 bits. Many machines also provide operations on larger and smaller word sizes. (Frequent forms are half-word and long- or double-word, although other forms are possible.) The natural word size may be different from the hardware word size. For example, the Motorola 680x0 is advertised as a 32-bit processor and readily manipulates 32-bit values (its natural word size). However, the physical word size for many early implementations of this instruction set is 16 bits, since the internal data paths and logic are all 16 bits wide. Thus, the performance of a particular processor can be less than that of other 32-bit processors, which require an extra cycle to make a second pass through the logic unit to generate a double-length result. It is, however, significantly faster than the competing 16-bit processors, where the extra precision is required to be explicitly implemented in software.



		In many modern machines, the operation vocabulary (instruction set) has become rather extensive, as the number of standard operations is large and the variations in parameters (including addressing modes) are many. If all actions are defined for all data types, the instruction set is said to have the orthogonal property (Table 1.4). Most machines include a common core of operations that include:



		add, subtract, multiply, divide,

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