The Central Processing Unit (CPU) is the core of your system, usually referred to as the "brain" of the computer.  The CPU is how the computer thinks, processing data provided by other components into a form that can be understood by a user.

How does a CPU work?

The job of a CPU is to handle instructions and calculations necessary for the PC to operate.  Without getting into the deeper complexities of system architecture, all CPUs operate on the same principle:  receive input, produce output (I/O).

For this article, let's think of the CPU as a worker and the PC itself as a workshop.  The CPU has some common knowledge and capacity to do work but it's going to need a little help in the form of materials, tools, and instructions.  This will be covered more in other articles.

What do the specs of a CPU mean?

When picking out a CPU for your system you'll find a few key specifications will be called out such a Clock Speed, Number of Cors, Socket, etc.  Together, these specs can provide an idea of what a CPU's performance is and can be key when comparing different products.

Clock Speed

Going from the top of the list, Clock Speed is an indication of how many clock cycles (aka ticks) a CPU goes through within a second measured in Hertz (Hz).  For example, a 3 GHz processor goes through 3 billion clock cycles per second.  It is worth noting however that Clock Speed is not the only indicator for a processor's performance, as other factors such as available cache, instruction set, and the number of processor cores will also have an effect on the overall performance of a CPU.

Taking into account these other specs and generational improvements in CPU technology, a 3GHz CPU from 5 years ago may get severely outperformed by a newly released 3GHz CPU.

Processor Cores

The core of a processor is the part which handles the executions of data.  In the past, most processors were single-core and limited to a single task (also known as a thread) at a time.  As CPU technology has improved we've seen the introduction of CPUs with multiple cores capable of handling multiple threads at once, and even the introduction of CPU cores capable of handling multiple threads at the same time.

Processor Cores are generally split into one of two categories:

• Physical Cores referring to the physical processor core(s) on a CPU die.
• Logical Cores referring to the number of effective CPU cores see by the system while in operation.  This is calculated as # of Physical Cores x Number of Threads per Core.

Performance Cores (P-Cores) and Efficiency Cores (E-Cores)

With newer Intel® Core™ processors, you may see callouts for P-cores and E-cores in the specifications sheet.  These refer to two specialized core types that can be included on a single CPU.  As the names imply, P-cores are CPU cores designed to maximize performance while  E-cores are designed to reduce power draw and maximize power efficiency.

Source:  Intel - How Intel® Core™ Processors Work

Socket

The cpu socket is the physical bridge that connects a CPU to a Motherboard.  CPU sockets come in a variety of different sizes and formats, with two primary types being used for consumer PCs:

• Land-grid Array (LGA) sockets are the most common type of socket, featuring pins in the socket that make contact with conductive pads on the underside of the CPU.  While originally more common with Intel® CPUs, newer AMD CPUs such as the AMD Ryzen™ 7000 series and AMD Ryzen™ Threadripper™ series utilize LGA sockets.
• Pin-grid Array (PGA) sockets are a less common socket type which features a series of holes that are filled by pins on the underside of the CPU to connect to the motherboard.  This type of socket is most common with AMD CPUs prior to the introduction of the AM5 socket, including the AM4 socket used by AMD Ryzen™ 5000 series CPUs.

When picking a CPU, it's important to make sure that the socket is an exact match between the motherboard and CPU.  It is incredibly rare for a CPU to be compatible with more than one socket, and you cannot mix and match CPUs and sockets across brands such as AMD and Intel.

Cache

Cache is a form of small, incredibly fast memory built into the CPU itself.  This particular spec is often overlooked, but can have a major impact on your system's performance.  Cache is broken down into several levels (i.e. L1, L2, and L3) which are used by the CPU to store data necessary for quick calculations:

• L1 - The smallest and fastest level of the cache, L1 cache is generally distributed on a per-core basis.
• L2 - Slightly larger and slower than L1, L2 cache is generally distributed on a per-core basis like with L1.
• L3 - The largest and slowest of the standard three cache levels, L3 is usually shared across multiple cores.

Further Reading

• How do I pick a CPU for my PC?
• Installing a CPU