Advanced RISC Machine( ARM) is a CPU architecture that was developed at the beginning of the 1980s by Acorn Computer and later further developed together with Apple. It is a RISC architecture that is used in many mobile devices, in cell phones, handhelds and notebooks but also as a system-on- chip( SoC) in the modules of industrial computers, in embedded systems, game consoles, data communication devices, consumer devices, micro devices and in digitalsignal processing. In embedded systems, it is the most widely used microprocessor.
Like most RISC processors, the ARM processor has a small instruction set, with all instructions executed in one clock cycle. Each instruction contains a 4-bit code that specifies a particular condition of the status register that must be satisfied in order to execute the instruction.
The development of the ARM processor
The 32-bit ARM microprocessors are numbered by generation; thus, the ARM1 stands as the first ARM prototype in the hierarchy. The ARM already had 16 32-bit registers, a 32-bit data bus and a 26-bit wide address bus in the ARM2 version. One of these registers served as a program counter. With about 30,000 transistors, the ARM2 required only about half as many transistors as other processor architectures. This is due to the fact that the ARM2 does not yet have an on-chip cache and is wired without microcode. This naturally also results in lower power consumption.
The ARM6, introduced at the beginning of the nineties, found its way into PDAs. The core of the ARM2 was essentially retained, so that the ARM6 managed with only 35,000 transistors. However, it has a SIMD computer architecture and has efficient instruction handling. In this constellation, the ARM6 can be completed with optional components to form a low-cost microcomputer.
The successor model ARM7 was used millions of times in cell phones and game consoles. The various licensees developed ARM variants which were characterized by performance but also by low power consumption. For example, the StrongARM, developed by Digital Equipment, was clocked at 233 MHz and required only 1 W of power.
The ARM11 is based on the processor architecture of the ARM6 and is designed for clock frequencies of several hundred megahertz up to even over 1 GHz. The ARM11 is used in automotive technology, wireless consumer electronics devices, WLANs and Bluetooth. Successors to the ARM11 are the Cortex processors.