How to choose a CPU: what matters and what fits your PC

A CPU (central processing unit, or processor) runs your programs and your games’ logic. Picking one is less about finding “the best” chip and more about two questions: will it work in your PC, and is it the right size for what you do.

One thing up front: RigFit shows specs and compatibility, from public sources we link on every part page. We don’t run speed tests, so we don’t publish frame rates or “X% faster” claims. Instead, we explain how to read other people’s benchmarks well.

The short answer

Upgrading? Start with your motherboard. The CPU must match its socket, and the board may need a BIOS update first.
Gaming? A modern 6- or 8-core chip suits most people. Your graphics card usually matters more.
Video editing, 3D rendering? More cores pay off, because that software can use them.
Office work, browsing, school? An entry chip with built-in graphics is plenty, and saves buying a graphics card.
Building new? Pick a current platform (AM5 or LGA1851) with DDR5 memory.

Compatibility first

Most CPU buying mistakes aren’t about speed. They’re about a chip that doesn’t fit, doesn’t boot, or needs a new board and memory. Check these four things in order.

1. Socket: the hard rule

The socket is the physical holder on the motherboard. Each CPU fits one socket and no other. There is no adapter. AMD and Intel sockets are never interchangeable.

The four desktop sockets RigFit covers today:

Socket	Brand	CPUs in our data	Boards in our data	Memory	Status
AM4	AMD	100	272	DDR4 only	Older platform, still a good upgrade path
AM5	AMD	61	275	DDR5 only	Current
LGA1700	Intel	82	320	DDR4 or DDR5, set by the board	Previous generation (12th, 13th, 14th gen Core)
LGA1851	Intel	22	108	DDR5 only	Current (Core Ultra 200S)

To find your socket, look up your motherboard model. On Windows, you can see it in System Information (search “msinfo32”, then look at “BaseBoard Product”). Or ask our checker, which finds the socket from the board name.

2. Chipset: what the board can do

The chipset is a second chip on the motherboard. Its name (B650, Z790, B550 and so on) tells you which features the board supports. Two boards with the same socket can behave differently:

Overclocking. On Intel, only Z-series boards (Z690, Z790, Z890) let you overclock an unlocked “K” CPU. On AM5, the A620 and B840 boards don’t allow CPU overclocking; B650, B850, X670 and X870 do.
PCIe speed. PCIe is the connection your graphics card and fast SSDs use. A newer CPU on an older board runs at the board’s speed. For example, an AM4 board with a B450 chipset runs a Ryzen 5000 CPU at PCIe 3.0, even though that CPU supports PCIe 4.0 on a B550 or X570 board.
Power delivery. A top-end CPU on a cheap entry board may work but run below its best.

3. BIOS: the step people miss

The BIOS is the small program on the motherboard that starts the PC. A board only knows the CPUs that existed when its BIOS was written. If your CPU came out after your board, the board may need a BIOS update before it will even start. Common cases:

Ryzen 5000 chips on AM4 boards with 300- or 400-series chipsets.
Ryzen 9000 chips on AM5 boards with 600-series chipsets (A620, B650, X670).
Intel 13th and 14th gen chips on 600-series boards (H610, B660, Z690).

How to handle it:

Find your board on its maker’s website and open the CPU support list. It names the first BIOS version that supports each chip.
Update the BIOS before you swap the CPU, while your old chip still works.
Buying a board for a new chip? Look for BIOS Flashback (names vary by brand). It updates the BIOS from a USB stick with no CPU installed.

BIOS updates also fix problems, not only add chips. In 2024 Intel released microcode fixes for instability in some 13th and 14th gen desktop chips, delivered through BIOS updates. Running a current BIOS is good practice either way.

4. Memory type: DDR4 or DDR5

Memory (RAM) comes in generations, and the slots are shaped differently. DDR4 sticks don’t fit DDR5 slots.

AM4: DDR4 only.
AM5 and LGA1851: DDR5 only.
LGA1700: either, but the board decides, not the CPU. In our data, 126 LGA1700 boards take DDR4 and 194 take DDR5. You can’t switch types without changing boards.

Each CPU also has an official memory speed. Faster kits often work, but only once you turn on the memory profile in the BIOS (called XMP on Intel and EXPO on AMD).

What the specs mean

Cores and threads

A core is one worker inside the CPU. A thread is a stream of work a core handles. Many cores can run two threads at once (Intel calls this Hyper-Threading, AMD calls it SMT).

Two catches:

Not all cores are equal. Recent Intel chips mix big “Performance” cores with smaller “Efficient” cores. A Core i5-14600K has 14 cores (6 big, 8 small) and 20 threads.
Not every core runs two threads. Intel’s Core Ultra 200S chips dropped Hyper-Threading: the Core Ultra 9 285K has 24 cores and 24 threads.

More cores help when software spreads its work out: video export, 3D rendering, compiling code, running many apps at once. Most games lean on a handful of fast cores.

Clock speed

Clock speed, in gigahertz (GHz), is how many cycles a core runs per second; “boost” is the top speed under light load. Compare clocks only within one family and generation. A newer chip at a lower clock can beat an older one, because it does more work per cycle (IPC, instructions per clock).

Cache and X3D

Cache is very fast memory inside the CPU that keeps often-used data close at hand. Games tend to benefit from a large cache.

AMD’s X3D chips stack extra cache on top of the processor. In our data, the 8-core X3D models carry 96 MB of L3 cache, against 32 MB on a regular Ryzen 5 7600. Reviewers generally find this helps in games and matters much less in other work. The trade-off is often a higher price than the non-X3D version of the same chip.

Integrated graphics

Some CPUs include basic graphics, enough for a desktop, video and light games. You can then run a PC without a graphics card, or keep it working while you troubleshoot one. If you always use a card, a chip without graphics can save money.

Intel: models ending in F have no graphics. The Core i5-14600KF launched at $294, against $319 for the 14600K with graphics.
AMD AM4: only the G models have graphics (34 of the 100 AM4 chips in our data).
AMD AM5: most have basic graphics (55 of 61 in our data). G models have stronger graphics.

Power (TDP) and cooling

TDP (thermal design power) is the maker’s guide, in watts, to how much heat the cooler must handle. The CPUs in our data range from 35 W to 200 W. AMD and Intel define it differently, and Intel also lists a higher “Max Turbo Power”, so treat TDP as a rough size, not an exact figure.

Also, coolers mount to sockets. Most AM4 coolers fit AM5, and LGA1700 coolers generally fit LGA1851, but check the cooler maker’s list.

PCIe lanes and generation

PCIe lanes are the CPU’s direct links to the graphics card and fast SSDs. Current desktop chips have enough for one graphics card and one or two fast SSDs; other devices go through the chipset. The useful check: the PCIe generation you get is the lower of the CPU’s and the board’s. Some chips also run lower than their siblings. AMD’s Ryzen 5000G models, for example, use PCIe 3.0.

Matching the CPU to what you do

Everyday use (browsing, office, video calls): a lower-cost chip with built-in graphics, such as a Core i3 or a Ryzen G model. Extra cores sit idle.
Gaming: 6 to 8 modern cores, a high boost clock, and plenty of cache. Put more money into the graphics card than the CPU.
Gaming plus streaming: 8 cores or more help. Modern graphics cards also have a video encoder that takes most of the streaming load off the CPU.
Editing, 3D, coding: core count matters most. Check benchmarks for the exact apps you use.

Tier	AM5 (Ryzen)	LGA1700 (Core)	LGA1851 (Core Ultra)
Entry	n/a	Core i3: median $134	n/a
Mid-range	Ryzen 5: median $229 ($179 to $299)	Core i5: median $223 ($167 to $319)	Core Ultra 5: median $247 ($184 to $309)
Upper mid-range	Ryzen 7: median $359 ($299 to $499)	Core i7: median $384 ($314 to $409)	Core Ultra 7: median $384 ($299 to $394)
High end	Ryzen 9: median $649 ($429 to $899)	Core i9: median $564 ($464 to $739)	Core Ultra 9: median $549 ($549 to $589)

The bottleneck idea, honestly

People say a CPU “bottlenecks” a graphics card. It means one part is waiting on the other. In a game, the CPU prepares each frame and the graphics card draws it. Whichever is slower sets the pace.

What bottleneck calculators skip: it depends on the game, the resolution and the settings. At 4K the graphics card usually sets the pace; at 1080p with a very fast card, the CPU shows more. Every PC has a bottleneck somewhere, and no single percentage can describe a CPU and graphics card pair.

The useful question is: in your games, at your settings, is your CPU holding you back? Reviews that test at your resolution answer that better than any calculator.

How to compare two CPUs

Use this checklist, in this order:

Same socket as your board? If not, add the price of a board (and maybe memory).
Does your board’s BIOS support it? Check the CPU support list.
Cores and threads, counting big and small cores apart.
Boost clock and generation. Compare clocks only within a family.
Cache, especially for gaming.
Integrated graphics: needed or not?
TDP and cooler: included or extra?
Total cost: CPU + any board + any memory + any cooler.

You can put two chips side by side on RigFit’s CPU comparison. It shows the specs, what differs, and which chipsets take each one.

Reading reviews and benchmarks critically

Benchmarks are useful, but only if you read them carefully:

Check the test setup. Gaming CPU tests usually pair each chip with the fastest graphics card at a low resolution, to make CPU differences visible. With your card and settings, the gaps are usually smaller.
Look for your apps. A rendering score says little about a game, and the reverse.
Be wary of one “overall score”. It hides how the tests were weighted. Prefer reviews that show many results and explain their method.
Cross-check. When two careful outlets agree, trust it more. Note the date, too: BIOS and driver updates can change results.
Mind small gaps. A few percent is rarely something you’ll feel.

Upgrade the CPU, or move to a new platform?

A drop-in upgrade (new CPU, same board and memory) is usually the cheapest step. It makes sense when your socket has faster chips than yours, your board supports them (perhaps after a BIOS update), and you mainly want more cores or cache rather than new features. AM4 is the classic case: many older AM4 boards can take a Ryzen 5000 chip after a BIOS update.

A new platform (new CPU and board, often new memory) makes sense when you already have the fastest chip your board supports, when you need newer features such as DDR5 or PCIe 5.0, or when your board gets no BIOS update for the chip you want.

Count the full cost. Moving from AM4 to AM5 means a new board and DDR5 memory as well as the CPU. Moving from LGA1700 to LGA1851 means a new board, and new memory too if yours is DDR4.

Common mistakes

Buying the CPU before checking socket and BIOS support.
Forgetting that a new platform needs new memory.
Buying an F model for a PC with no graphics card.
Forgetting the cooler when none is in the box.
Buying a top CPU for gaming while keeping a weak graphics card.
Trusting one benchmark score or a bottleneck percentage.

FAQ

Will a new CPU work with my motherboard? Only if it uses the same socket and your board’s BIOS supports it. Check the board maker’s CPU support list, or enter your board in our checker.

Do I need to update my BIOS before installing a new CPU? If the CPU came out after your board, probably yes. Update first, using the old CPU, unless your board has BIOS Flashback.

How many cores do I need for gaming? For most people, 6 to 8 modern cores. Newer cores and more cache usually matter more than a higher count.

Is Intel or AMD better? Neither wins across the board, and it changes with every generation. Pick the platform that fits your budget and upgrade plans, then compare chips at your price.

Can I use DDR4 memory with a new CPU? On AM4, yes (DDR4 only). On AM5 and LGA1851, no (DDR5 only). On LGA1700 it depends on the board.

Does the CPU come with a cooler? Some do, many don’t. Unlocked and high-end models are often sold without one. Check the box contents before you buy.

See which CPUs fit your PC

Tell us your motherboard and current CPU, and we’ll show the upgrades that fit, with BIOS and memory notes. Every spec links to its source.

See which CPUs fit your PC

Already have two chips in mind? Compare them side by side.