In the decades since the Central Processing Unit, or CPU, has been invented and developed, engineers have made several advancements and have incorporated several important features to include in its architecture, enabling the CPU to process data as efficiently as possible. Over time, two prominent architectures have emerged for introducing instruction sets to the CPU - these are known as RISC and CISC. RISC focuses on simplicity, and employs a smaller set of highly optimized instructions to enhance speed and efficiency. Conversely, CISC embraces complexity, and offers a broad range of instructions capable of executing multifaceted tasks in fewer steps. Understanding the differences, advantages, and disadvantages of RISC and CISC is crucial for engineers and developers when determining the best architecture for their specific needs.
Image by What is RISC?
RISC stands for Reduced Instruction Set Computer, and is best defined as a computer processor set that works to simplify and execute instructions, utilizing small, highly optimized instruction sets to execute commands quickly. RISC is used in computer architecture design and turns complicated ideas into simpler information for the CPU to process. With the simplicity of RISC, instruction sets are processed much faster and often lead to greater efficiency and performance for the device that is using this design. In practice, RISC is often found in various designs for mobile, battery-operated devices and embedded systems.
What is CISC?
Like RISC, CISC is also an instruction set that is used in computer architecture design. However, the approach differs quite a bit. CISC, which stands for Complex Instruction Set Computer, offers more dynamic communication. CISC features the ability to take in large and diverse sets of instructions, each of which are capable of performing multiple low-level operations. Examples of these operations include memory access, arithmetic, and logic, all of which can be performed in a single command. As a result of this flow and design, CISC is able to execute more complex tasks with fewer instructions leading to a much more simplified programming design. Most commonly, CISC is found in x86 architecture that is utilized often in PCs.
Advantages and Disadvantages of RISC
The use of RISC brings with it a mix of advantages and disadvantages to CPU architecture. Thanks to the simplicity of RISC design, it uses lower power consumption and utilizes simple instruction sets to execute actions. As a result of all this, RISC also has an execution rate that is much faster than CISC. Depending on what the CPU is being used for, RISC could be the best choice. Still, however, there are disadvantages to RISC that should be noted.
For one, RISC requires an increased number of instructions. Since RISC operates using very simple instructions, any complex task needs to be broken down into several, easy-to-execute instruction sets. Because of the larger number of instruction sets to complete tasks, there is a need for increased storage capacity. Additionally, RISC’s use of simplified instruction sets also makes it less flexible for specialized tasks that require more intricate commands. Due to all of these factors, RISC may not always be the optimal choice depending on the goals of your project and CPU design.
Advantages and Disadvantages of CISC
CISC also offers various advantages that may be best suited for specific CPU applications. For instance, its advantages include efficient memory usage, smaller code size, and a general commonality as CISC processors are frequently used in CPU architecture across various devices. Additionally, CISC can handle more complex data by using powerful, multi-step instructions that can perform intricate operations in a single command, reducing the need for multiple simpler instructions. In turn, this is why not as much memory storage is needed and also why CISC commands require less code. These benefits are what sometimes makes it the best choice for a CPU design.
There are still disadvantages though, and these disadvantages can be the deciding factor when it comes to using CISC or RISC. A disadvantage of CISC to consider is its consumption of power. Because CISC works with more complex instructions, it needs a much higher amount of power to process data when compared with RISC. Another disadvantage is the complexity of CISC design. Although its ability to process complex instruction sets is a benefit of CISC, it also makes design and manufacturing more difficult. A third disadvantage is the slow execution time, which is another result of using more advanced and complex instruction sets.
RISC vs. CISC In Different Applications
Knowing what both instruction sets are capable of often leaves developers having to decide which set to use within their system. So, which one is the best option to work with? Well, it depends on the needs of an individual project and the preferences of the engineer.
RISC is most often found in the CPU architecture of mobile devices, server designs using ARM, and other embedded systems. Mobile devices utilize RISC-based architecture due to its power efficiency, making RISC ideal for battery-operated devices. We also see RISC often used in embedded systems devices, including IoT (Internet of Things), which is a network of interrelated devices that connect and exchange data with other IoT devices and the cloud. RISC is also often used in the automotive industry for features like Electronic Control Units that can be used for vehicle components such as Advanced Driver Assistance Systems.
On the other side, CISC is typically found in desktop processors, including those that use the x86 architecture, or other high-performance workstations. Since CISC operates with more complex instruction sets, it is often used in devices that reflect this need. Additionally, CISC can be found in large computer mainframes that rely on the processors security and ability to handle large, complex workloads. Several high-end gaming consoles also rely on CISC-based architecture because of the high performance demands they have for intricate gaming environments.
Conclusion
Choosing between RISC and CISC architectures depends on the specific requirements of a project, since each has its unique strengths and weaknesses. RISC works best in environments where power efficiency, speed, and simplicity are most important - which makes it ideal for mobile devices, embedded systems, and other applications where high performance and low power consumption is critical.
On the other hand, CISC’s ability to execute complex instructions with fewer lines of code makes it a preferred choice for desktops, high-performance workstations, and systems that require compatibility with a wide range of software. Both architectures have proven their value over time, and their continued growth ensures that they remain relevant as technology and design continues to evolve. Ultimately, the decision to use RISC or CISC should be guided by the specific needs of the application-while also balancing performance, power consumption, and complexity.
How Total Phase Supports Testing CPU Functionality in Embedded Systems
At Total Phase, we offer a wide array of tools that assist engineers with developing embedded systems and testing the validity of various system components, including the CPU and how it interacts with and responds to other devices. Tools like our Aardvark I2C/SPI Host Adapter or Promira Serial Platform allow engineers to emulate I2C or SPI master or slave devices, allowing them to prototype entire systems and their functionality. The Beagle I2C/SPI Protocol Analyzer, on the other hand, can capture and monitor I2C and SPI bus data occurring between devices in real time. This allows engineers to quickly pinpoint bus errors and their origins for easier system debugging.
For more information on these tools, and others that we offer, please feel free to contact us or request a demo.