Published: 10 June 2024
Contributors: Josh Schneider, Ian Smalley
A microprocessor is the predominant type of modern computer processor. It combines the components and function of a central processing unit (CPU) into a single integrated circuit (IC) or a few connected ICs.
Like CPUs, microprocessors are commonly thought of as the “brain” of the computer. Unlike traditional CPUs, microprocessors integrate the arithmetic, logic and control circuits of more traditional CPUs into a single multipurpose, clock-driven and register-based digital circuit.
While the terms CPU and microprocessor are often used interchangeably, a microprocessor is essentially an all-in-one CPU on a single chip. This single-chip design reduces the number of vulnerable electrical connections, improving reliability by reducing potential points of failure. As such, microprocessors have almost completely replaced traditional, multicomponent CPUs.
Before microprocessors, computers used racks of ICs to accomplish the computer’s main computing functions. In 1971, a significant shift occurred in computing technology with the introduction of the Intel 4004, the first commercially available microprocessor. This groundbreaking device, designed by Federico Faggin, was not just a response to a request for 12 custom microchips for a calculator from Japanese electronics maker Busicom. It was a landmark moment that revolutionized the way we think about computing, as Intel, instead of producing 12 individual chips, created a general-purpose logic device.
Underpowered by today’s standards, the Intel 4004’s architecture operated at a clock speed of 740 kHz and could only process data streams with a maximum of 4 bits, also known as a “nibble.” While the 4004 is weak compared to modern 8-bit to 64-bit microprocessors, it is universally considered to be a revolutionary breakthrough in circuitry. As predicted by Moore’s law, rapid semiconductor technology development led to major processing power improvements. Manufactured by leading suppliers, such as Intel and Pentium, and used by all major tech companies, such as IBM®, Microsoft and Apple, microprocessors power thousands of systems and applications from TV remote controls to the International Space Station.
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Modern microprocessors combine millions of small transistors, resistors and diodes assembled on a semiconductor material to create the key components of a CPU. These components are arranged into various types of unique computer architecture to perform computations and run instructions. An average microprocessor's functions can be broken down into four main steps.
- Fetch: The microprocessor retrieves (or "fetches") instructions from computer memory. The fetch process can be initiated by automatic or manual input.
- Decode: The microprocessor "decodes" the instructions, essentially interpreting the input or command into a request and instigating a specific process or computation.
- Execute: Simply put, the microprocessor performs the required or requested operation.
- Store: The result of the execution is committed to the computer’s memory.
Microprocessors can complete these processes by combining the main components of a CPU into a singular circuit. The key components of a microprocessor are the following:
- Arithmetic logic unit (ALU): The main logic unit of the CPU, this component performs logical operations, including mathematical calculations and data comparisons.
- Control unit (CU): The CU circuit interprets instructions and initiates their execution, directing the processor's basic operations.
- Registers: Registers provide small, fast memory storage used by a CPU to temporarily hold data and instructions during computational processes.
- Cache memory: Microprocessors and CPUs use cache memory, a high-speed form of memory located close to the CPU, to store frequently accessed data to accelerate performance.
- Busses and bus interfaces: Bus interfaces provide entry and exit points for data to travel across various groups of wires (referred to as busses), such as the address bus or data bus. Busses and interfaces physically connect different internal components, enabling and facilitating communication within the CPU and other peripherals like input/output (I/O) units.
- Transistors: One of the main building blocks of ICs, transistors are small semiconductors that regulate, amplify and generate electrical currents and signals. They can also act as simple switches or be combined to form logic gates. The number of transistors is a common indicator of microprocessor power.
- Processor cores: Individual processing units within microprocessors are known as cores. Modern processors frequently incorporate multiple cores (dual-core, quad-core) allowing for parallel processing by enabling the performance of multiple tasks simultaneously.
- Clock: Although not all microprocessors contain an internal clock, they are all clock-driven. Some rely on external clock chips, which are known for improved accuracy. Whether internal or external, a microprocessor's clock cycle determines the frequency at which it will carry out commands. Modern clock speeds are measured in megahertz (MHz) and gigahertz (GHz).
The architecture of a microprocessor refers to various design and organization methodologies of the processor’s various CPU components. These are the key architectural elements of a microprocessor:
- Instruction Set Architecture (ISA): The microprocessor’s ISA defines the instruction set that the processor can perform. ISAs like the Reduced Instruction Set Computer (RISC) and Complex Instruction Set Computer (CISC) architectures provide various methods for data processing, offering varying levels of performance, reliability and speed suitable for different types of applications.
- Data path: A microprocessor’s data path dictates the order in which data moves through the microprocessor’s components (buses, ALU, registers), influencing overall performance.
- Control path: Similar to the data path, the control path element of a microprocessor’s architecture instructs the sequence of operations and manages data transmission within the CPU.
- Memory hierarchy: The memory hierarchy is a critical component of the processor’s architecture, providing a structure for different levels of memory (cache, registers, RAM) to optimize for efficient data access and retrieval speed.
Microprocessors range in power, performance, architecture methodologies, size, energy consumption and many other variables and are designed for all sorts of applications. General-purpose microprocessors are common in personal computers and mobile devices, while specialized high-performance units like Digital Signal Processors (DSPs) are designed for demanding tasks like audio, speech, video and image processing.
The following are some of the main types of microprocessors.
These versatile microprocessors are found in a wide range of common applications and devices, such as laptops and servers.
Although it is more accurate to say that microcontrollers contain microprocessors, these types of chips also feature all the additional components necessary for a functional computer, namely built-in memory. Microcontrollers function like microcomputers and are preferred for controlling specific elements within embedded computer systems. Small, low-power microcontrollers do not require complex operating systems to run and are commonly used in the automotive industry to optimize Engine Control Units (ECUs), Advanced Driver-Assistance Systems (ADAS) and infotainment units, as well as a vast range of consumer electronic devices and even industrial automation.
DSPs are specialized for high-speed numeric calculations and are often used for demanding tasks like audio processing, telecommunications and image processing. They might also be found in applications requiring the interpretation of analog to digital signals, such as weather sensors. DSPs are commonly used in military applications like surveillance drones and other autonomous aircraft.
ASIC microprocessors are designed for specific tasks and are customized to meet the specific demands of various applications. Some examples of ASIC microprocessors include custom chips for game consoles or cryptocurrency mining. DSPs, GPUs and other types of specialized microprocessors are technically ASICs as well.
GPU microprocessors are specially designed for the demanding task of rendering digital video and graphics requiring high-powered performance and parallel processing. Critically important for high-end gaming, powerful GPU microprocessors are also commonly used in cryptocurrency mining and are known for high power consumption.
A type of ASIC microprocessor specifically optimized for processing network data packets most frequently used in telecom switches, routers and network security devices.
Coprocessors, such as floating-point units (FPUs), are designed to provide auxiliary support for a system’s main CPU to boost performance during certain demanding tasks, such as carrying out advanced scientific calculations or complicated mathematical formulas.
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A central processing unit (CPU) is the primary functional component of a computer. The CPU is an assemblage of electronic circuitry that run a computer’s operating system and apps and manages a variety of other computer operations.
Data storage refers to magnetic, optical, or mechanical media that records and preserves digital information for ongoing or future operations.
A microcontroller unit (MCU) is essentially a small computer on a single chip. It is designed to manage specific tasks within an embedded system without requiring a complex operating system.
A field programmable gate array (FPGA) is a versatile type of integrated circuit designed to be programmable on the hardware level to suit different purposes such as high-performance computing (HPC) and prototyping.
Field programmable gate arrays (FPGAs) and microcontroller units (MCUs) are two types of commonly compared integrated circuits (ICs) that are typically used in embedded systems and digital design. Both FPGAs and microcontrollers can be thought of as “small computers” that can be integrated into devices and larger systems.
A graphics processing unit, also known as a graphical processing unit or GPU, is an electronic circuit designed to speed up computer graphics and image processing on various devices, including video cards, system boards, mobile phones and personal computers (PCs).