AIX Version 4.3 Differences Guide

Chapter 3. 64-Bit Enablement
This chapter covers the introduction of 64-bit systems and the support provided in
AIX Version 4.3 for these systems. In the first section, an introduction to 64-bit
architectures and its benefits is provided, including the hardware and software
aspects of 64-bit implementations. The design chosen for RS/6000 systems and
the AIX operating system is also explained.
The second section describes the changes made to the core operating system
that are necessary to run AIX on 64-bit hardware and enable 64-bit applications.
These changes include modifications to the basic application development tools
like compiler, linker, and debugger, and other tools that operate on object files.
3.1 Introduction to 64-Bit Computing
The following sections describe some of the features of the new 64-bit
environment.
3.1.1 64-Bit Architecture and Benefits
From an operational point of view, an architecture is said to be 64-bit when:
• It can handle 64-bit-long data; in other words, a contiguous block of 64 bits (8
bytes) in memory is defined as one of the elementary units that the CPU can
handle. This means that the instruction set includes instructions for moving
64-bit-long data and instructions for performing arithmetic operations on
64-bit-long integers.
• It generates 64-bit-long addresses, both as effective addresses (the
addresses generated and used by machine instructions) and as physical
addresses (those that address the memory cards plugged into the machine
memory slots). Individual processor implementations may generate shorter
physical addresses, but the architecture must support 64-bit addresses.
The benefits of 64-bit architectures can be summarized as follows:
• Extended-precision arithmetic. The ability to use very long integers in
computations is a feature that can be very useful in specialized applications.
• Access to large data sets. The ability to create and maintain very large file
systems is increasingly important for many users. In particular, data
warehousing applications, scientific, and multimedia applications frequently
require these features.
• Large address spaces. A 64-bit architecture has the capability of addressing
huge address spaces. You should realize that the step to 64-bits is much more
than just a doubling of 32-bits. In terms of addressability, it represents a four
billion-fold increase. With clever exploitation, these large address spaces can
result in spectacular performance improvements or gains in productivity
through simplified programming of very large technical problems.
The ability to handle large address spaces is considered the greatest potential
benefit for users since, in the future, complex applications such as large
databases, large numeric applications, and multimedia environments will need to
manage and operate on larger data sets. Since internal memory is much faster
than most storage devices, the ability to fetch and keep more data in memory,
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