Modern computers especially desktop PCs nowadays have many CPU cores, even for an entry level CPU like Intel i3 or Ryzen 3 where these days they are 4-cores designs.
Back in the day, mid tier CPUs were typically 4 cores, while the high end ones were often 8 cores. Today, most mid-range CPUs are usually 6 or 8 cores, while high-end ones often have 10 or more cores, though for gaming some of the fastest CPUs are still 8-core models with extra cache.
But when playing games, people using monitoring tools like RTSS may notice only a few cores are busy while the rest look almost idle. If games aren't using all the cores, what's the point of having all that, are these extra cores 'useless'?
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1. Some work must happen in order
Many parts of a game depend on steps being done in a specific order. The game needs to know what happened before it can decide what happens next. For example, enemy movement may depend on player position, and physics updates may depend on earlier calculations.
Because of this, some work cannot be split safely across many cores. Extra cores may just wait until the main task finishes.
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2. The cost of splitting work
This is about adding extra work behind the scenes, like coordinating tasks and making sure results arrive at the right time. The game has to be written in a way that supports it, not something a CPU does automatically by itself.
That coordination itself uses CPU time. In some cases, using more cores can actually slow things down instead of speeding things up. This can happen when the overhead becomes larger than the benefit.
└─ Programming with many cores is difficult
Writing code for one core is much simpler. Writing code that runs correctly across many cores is harder and more risky. Bugs can appear only sometimes, depending on timing, which makes them difficult to find and fix.
Because games must run smoothly every frame, developers often choose safer designs instead of pushing extreme CPU parallel usage.
3. There may not be enough independent tasks
For many games, there are not many separate CPU jobs that can run at the same time every frame. Some tasks like AI updates or physics calculations can be shared across cores, but they usually need to be combined again before the frame is finished.
That combining step can become a limit, even if parts of the work were done in parallel.
4. GPUs already do the parallel work
The most parallel part of games is graphics rendering which is usually done by the GPU.
The CPU mostly handles coordination, logic, and decisions. Those tasks are often more sequential by nature.
5. More cores does not always mean better performance
Using more CPU cores takes more development time and testing. Games also need to run well on common systems, not just high-end ones. Because of this, developers often focus on performance that works well for most players.
In many cases, faster individual cores matter more than having many unused ones.
6. It depends on the type of game
Some games may benefit more from multiple CPU cores, like strategy games, simulations, or games with many independent units which can sometimes use more parallel processing.
On the other hand, fast action games often rely more on quick, ordered updates and GPU power, so extra CPU cores may not help much.
In short, the issue is that not all game work can be split easily, safely, or cheaply. Extra cores often sit idle because using them would add complexity with limited benefit, not because they are useless. More cores can help in just some situations.
Source: Reddit