Page 23 - ARM 64 Bit Assembly Language

6Chapter 1

Micro, was based on the same processor that Apple Computer had chosen for their Apple II
line of computers; the 8-bit 6502 made by MOS Technology. As the 1980’s approached, mi-
crocomputer manufacturers were looking for more powerful 16-bit and 32-bit processors. The
engineers at Acorn considered the processor chips that were available at the time, and con-
cluded that there was nothing available that would meet their needs for the next generation of
Acorn computers.
The only reasonably-priced processors that were available were the Motorola 68000, (a 32-bit
processor used in the Apple Macintosh and most high-end Unix workstations), and the In-
tel 80286 (a 16-bit processor used in less powerful personal computers such as the IBM PC).
During the previous decade, a great deal of research had been conducted on developing high-
performance computer architectures. One of the outcomes of that research was the develop-
ment of a new paradigm for processor design, known as Reduced Instruction Set Computing
(RISC). One advantage of RISC processors was that they could deliver higher performance
with a much smaller number of transistors than the older Complex Instruction Set Computing
(CISC) processors such as the 68000 and 80286. The engineers at Acorn decided to design
and produce their own processor. They used the BBC Micro to design and simulate their new
processor, and in 1987, they introduced the Acorn Archimedes. The Archimedes was arguably
the most powerful home computer in the world at that time, with graphics and audio capabil-
ities that IBM PC and Apple Macintosh users could only dream about. Thus began the long
and successful dynasty of the Acorn RISC Machine (ARM) processor.
Although their technology was superb, Acorn never made a big impact on the global com-
puter market. Acorn eventually went out of business, but the processor that they created has
lived on. It was re-named to the Advanced RISC Machine, and is now known simply as ARM.
Stewardship of the ARM processor belongs to ARM Holdings, LLC which manages the de-
sign of new ARM architectures and licenses the manufacturing rights to other companies.
ARM Holdings does not manufacture any processor chips, yet more ARM processors are pro-
duced annually than all other processor designs combined. Most ARM processors are used as
components for embedded systems and portable devices. If you have a smart phone or simi-
lar device, then there is a very good chance that it has an ARM processor in it. Because of its
enormous market presence, clean architecture, and small, orthogonal instruction set, the ARM
is a very good choice for learning assembly language.

Although it dominates the portable device market, the ARM processor family has almost no
presence in the desktop or server market. However, that may change. In 2012, ARM Holdings
announced the ARMv8-A architecture, which introduced a new 64-bit instruction set, referred
to as AArch64, or ARM64. This represents the first major redesign of the ARM architecture
in 30 years. Most processor families have been extended to include 64-bit instructions, while
simultaneously supporting the older instruction set(s). ARM chose another route. The pro-
cessor operates either in ARM64 mode or ARM32 mode, and the two modes are completely