The ARM microcontroller was first invented in the mid 1980s by Acorn Computers Ltd in Cambridge, England. The original aim was to produce a low-cost and low-power processor for Acorn’s personal computer range, particularly the BBC Micro home computer. After successful in-house use in Acorn’s products, ARM Holdings was spun out as a separate company in 1990 to license and develop the ARM architecture for wider applications.
The origins of ARM in Acorn Computers
In 1983, Acorn Computers was a successful British computer company known for its BBC Micro home computer. As the successor to the popular BBC Micro was being developed under the code name BBC Master, Acorn realized they needed a new processor design that was inexpensive, low-power, and provided good performance.
At the time, microprocessors were getting more complex and power hungry. Acorn determined that existing off-the-shelf processors from the likes of Intel, Motorola and Zilog were not suitable for their needs. Instead, they decided to design their own custom microprocessor in-house.
The team that designed the new microprocessor was led by Sophie Wilson and Steve Furber. Their initial design, dubbed the Acorn RISC Machine or ARM, was a 32-bit Reduced Instruction Set Computer (RISC) processor that executed instructions in a single cycle.
The first test silicon for the ARM1 chip came back in late 1984. After bugs were ironed out, it ran its first program in April 1985. The ARM1 was utilized in the BBC Master line of computers starting in 1986.
Key design features of the original ARM architecture
The ARM1 established the guiding principles of the ARM architecture that enabled high performance at very low cost and power:
- RISC load/store architecture – Simple instructions that execute in a single cycle.
- Highly efficient coding – Only 23% of die space used for ARM1 logic.
- Few registers – More instructions per byte compared to CISC.
- Joint development of hardware and BBC BASIC compiler.
- Efficient memory access using 3-stage pipeline.
- Low transistor count – Only 25,000 transistors in ARM1.
- Low power – 0.1mA/MHz power consumption.
The efficiency of the RISC architecture and tight compiler integration allowed ARM1 to deliver 4.8 MHz clock speeds while consuming only 1W of power. This provided Acorn a substantial performance boost over competing solutions while meeting stringent cost and thermal constraints of consumer electronics at the time.
Evolution of ARM microarchitecture 1985-1990
Following the success of ARM1 in Acorn computers, iterative improvements were made to the ARM microarchitecture over the next few years:
- ARM2 – Introduced in 1986, added support for virtual memory and increased clock speed to 8MHz.
- ARM3 – Launched in 1987, major redesign raised clock speed to 25MHz.
- ARM6 – Unveiled in early 1990s, included memory management unit and floating point unit options.
These changes increased performance and capabilities while retaining power efficiency. The ARM processor quickly became popular within Acorn for use across its computer line from embedded systems to desktops.
Birth of ARM Holdings and licensing model
By the late 1980s, Acorn realized the ARM architecture could be highly successful in the wider embedded computing market beyond just Acorn products. Many companies were looking for a low-cost, power efficient yet high performance RISC processor.
In late 1989, Acorn spun off its microprocessor design division into a new company called Advanced RISC Machines Ltd, which was soon renamed ARM Holdings. ARM Holdings would specialize in licensing and further development of the ARM architecture.
This allowed the ARM architecture to be commercialized beyond Acorn and used in embedded systems like set-top boxes, routers, hard disk drives, printers and mobile phones. Major companies like Apple, DEC, Intel, Nintendo, Nvidia and others took ARM licenses.
The licensing model enabled wide adoption of ARM processors throughout the electronics industry, driving volumes up and costs down.
Emergence of ARM cores for embedded and mobile markets
During the 1990s and 2000s, ARM Holdings worked closely with its licensees to tailor the ARM architecture for embedded systems and mobile devices:
- ARM7 – Introduced ARMv3 ISA and thumb instruction set, enabling improved code density.
- ARM9 – ARMv5 ISA provided DSP extensions and Jazelle DBX Java acceleration.
- ARM11 – Superscalar core in early 2000s targeted at embedded applications.
- Cortex – Launched in 2004, customizable cores scale from microcontrollers to application processors.
This drove rapid adoption in the mobile phone market, which valued ARM’s low power and cost advantages. By the mid 2000s, ARM cores were in billions of chips powering smartphones, tablets, home electronics and more.
Advanced capabilities in newer ARM core designs
ARM Holdings has continued innovating the ARM architecture with advanced capabilities while retaining power efficiency:
- Out-of-order execution in Cortex-A12 for higher performance.
- TrustZone security extensions in Cortex-A8 against malware.
- NEON SIMD engine since Cortex-A8 speeds multimedia and signal processing.
- Symmetric multiprocessing in Cortex-A9 improves multi-threaded performance.
- 64-bit instruction set in Cortex-A53 extends addressable memory.
- DynamIQ reconfigurable multi-core designs in Cortex-A65/A75.
Today, ARM remains the dominant architecture in embedded electronics and mobile computing, with ARM cores inside over 160 billion chips and climbing.
Summary of key ARM microcontroller milestones
Here are some of the major milestones in the multi-decade history of the ARM microcontroller:
- 1983 – Acorn initiates project to design a RISC microprocessor for upcoming BBC Master computer.
- 1985 – ARM1, the first ARM processor, fabricated and runs first program.
- 1986 – ARM2 raises performance and adds virtual memory support.
- 1990 – Advanced RISC Machines spins out from Acorn to create ARM Holdings.
- 1991 – Apple selects ARM processor for Newton PDA, exposing ARM to wider market.
- 1997 – ARM enters mobile phone market, now its biggest segment.
- 2009 – Cortex-A8 brings out-of-order execution to ARM cores.
- 2011 – ARM unveils first Cortex-A15 core with 40-bit physical addressing.
- 2012 – Cortex-A53 delivers high performance 64-bit capabilities.
- 2021 – ARM announces v9 architecture and SVE2 vector extensions.
From humble beginnings in a British microcomputer, ARM has become the most pervasive microprocessor architecture today powering billions of chips and electronic devices worldwide.
