A central processing unit (CPU) is the 'brain' of a computer and executes the instructions given by an operating system and the software running on it. Over the years, CPUs have undergone significant development, from processors with one CPU core to multi-core systems. Nowadays you often hear terms like single-core, dual-core, quad-core or even octa-core, and threads are also discussed. But what exactly are these CPU cores, and how do they differ from threads?
What is a CPU core?
A CPU core (also known as a 'processor core') is the physical processing unit within a CPU. Each core can be considered a separate mini-processor that can execute instructions independently. In the past, during the era of single-core CPUs, a processor had only one core and could essentially execute only one main task (or a sequence of instructions) at a time. Nowadays, most CPUs are multi-core, which means that multiple cores reside within one physical processor unit. These cores can execute different tasks simultaneously. Some key properties of a CPU core are:
- A CPU core has its own processing and control units. This means that each core within the CPU has its own resources (such as an ALU – Arithmetic Logic Unit) to process instructions.
- Often, each core has its own cache memory (L1 and L2 cache) for fast access to frequently used data and instructions. Additionally, there is usually a shared L3 cache that is common to all cores within the same CPU. The better the cache architecture, the faster the cores can operate, since the main memory (RAM) is relatively slow compared to this cache memory.
- Multiple cores make it possible to process several tasks in parallel. This is called 'hardware parallelism'. This benefits your system’s performance, especially if you multitask (for example, running multiple programs at the same time).
- Each core operates at a certain clock speed (for example, 3.0 GHz). This speed determines how many clock cycles per second occur during which instructions can be processed. A higher clock speed generally means more performance, but also higher energy consumption and increased heat production.
What is a CPU thread?
Until the early 2000s, most computers contained a single CPU core. Software at that time already made use of so-called 'software threads.' Programs can create multiple software threads themselves to distribute tasks. Switching between software threads is faster than completely switching between processes. This process happens so quickly that it appears as if processes are executed in parallel.
In 2005, the first dual cores hit the market. A single CPU could now utilize multiple cores and/or hardware threads (CPU threads, Hyper-Threading in Intel, SMT in AMD) to actually execute tasks in parallel. Hardware threads simply mean that one physical CPU core presents itself to the operating system as two (or more) logical cores. This is also known as 'multithreading.' The CPU core shares certain physical components, but has multiple registers and processing units to work on more than one thread per CPU cycle.
Difference between CPU cores and threads
Physical vs logical:
- CPU cores are physical processing cores in the CPU.
- Threads perform logical/virtual tasks. Threads are usually managed by the operating system or by hardware techniques such as Hyper-Threading.
Parallel processing:
- Cores truly execute tasks in parallel, each with its own hardware.
- Threads can also run in parallel, but their efficiency strongly depends on the underlying hardware. If you have one physical core and you start multiple threads, the system will switch between the threads (which affects performance).
Performance differences:
- Multiple cores provide genuine performance gains for processor-intensive tasks (such as video editing, rendering, or running multiple processes in parallel).
- Hyper-Threading/SMT (extra threads) can give a performance boost, but often less than having additional physical cores. With SMT, one thread might have to wait when the other thread needs the same hardware components.
Resources:
- CPU cores have their own essential components (such as processing and control units and part of the cache).
- Threads largely share the available hardware resources of the CPU core.
Why are multiple cores and threads important?
Somewhat obvious, but the advantage of using multiple cores and threads is the performance gain:
- With multiple cores, you can execute more tasks simultaneously. This allows the operating system (and the software running on it) to use the hardware more efficiently. With a single core, tasks would have to be switched continuously, leading to delays. Different applications can run on different cores or be distributed across the available cores and threads. This keeps the system responsive, even when running heavy software.
- Tasks such as video rendering, photo editing, and 3D modeling can be divided into smaller subtasks (parallel processing). This significantly speeds up the processing.
More CPU cores does not always mean faster
Not all software is equally optimized for multiple cores or threads. This is also true for your personal computer; for instance, with games: a CPU with many cores does not always run faster than one with fewer cores but a higher clock speed—it depends on how the game is programmed.
Furthermore, two CPUs with the same number of cores can have significantly different performance levels if they are from different generations. A modern CPU core is often more efficient, has a larger and faster cache, and supports newer instruction sets.
Lastly, heat production is also an important factor to keep an eye on: The more cores and the higher the clock speed, the more heat a CPU can generate. Adequate cooling is necessary to allow the CPU to run at its maximum speed without overheating.