Itanium® Architecture for Programmers: Understanding 64-Bit Processors and EPIC Principles

2.5. Itanium Information Units and Data Types

The basic information unit for the Itanium architecture is the 8-bit byte. Individual bytes are given 64-bit addresses, but it is also important to understand that groups of adjacent bytes have addresses, as shown in Figure 2-5. These multibyte units include the 16-bit word (2 bytes), the 32-bit double word (4 bytes), and the 64-bit quad word (8 bytes). For little-endian systems, such units are addressed by the low-order byte of the group. Similarly, the addresses of the higher-order bytes within the larger information units take on successive values beyond the address of the lowest-order byte.

Figure 2-5. Itanium information units

In the convention that has been used by Intel and Digital Equipment ...