From time to time, people ask this question. Computers can use RAM as storage, so why not do the opposite. If M.2 SSDs are already very fast, why not use them as RAM.
At first, this sounds reasonable. But when you look at how computers actually work, it usually does not work well.
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This already happens, but only in a limited way
Most computers already use storage to help RAM. This is called swap or paging.
When RAM is almost full, the system may move data that is not used much onto the SSD. This gives more space to programs that are still active. It works, but the system usually becomes slower when this starts happening.
This is not the same as replacing RAM. It is only a temporary solution when memory is running out.
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The real issue is delay, not transfer speed
Many people focus on speed numbers. Modern M.2 SSDs can transfer a lot of data per second. Older RAM can look slower when you only compare these numbers.
But memory is not about moving large files. It is about how fast data arrives after the CPU asks for it.
RAM responds very quickly. SSDs respond much later, even if they transfer data fast after that. This delay happens every time the CPU needs new data, again and again.
Programs expect memory to respond almost immediately. When it does not, performance drops a lot.
CPUs are designed around how RAM behaves
RAM is directly connected to the CPU’s memory system. CPU caches and scheduling depend on memory being fast and predictable.
SSDs do not behave this way. They are accessed through controllers, queues, and drivers. Even fast SSDs need extra steps before data is ready.
To make SSDs act like RAM, the CPU, operating system, and software would probably need major changes. That is not easy to do.
Wear is another practical concern
RAM can be written to continuously without problems. SSDs are different.
SSDs wear down over time as data is rewritten. Using them like RAM, where data changes constantly, would likely reduce their lifespan. Swap avoids this because most swapped data stays unchanged for long periods.
This may not be the main limitation, but it adds another downside.
Some special cases exist, but they are uncommon
There have been technologies designed to sit between RAM and storage. Intel Optane is one example.
It had much lower delay than normal SSDs and required special hardware support. Even then, it usually worked together with RAM, not as a full replacement. It was also expensive and not widely used.
This shows how difficult the problem is.
The conclusion is...
Using an M.2 SSD as real RAM can exist in limited forms, but it generally does not work well.
Performance often suffers and systems are not designed for this. The disadvantages are larger than the benefits.
SSDs work very well for storage while RAM works very well for active memory. Trying to treat them as the same thing usually leads to worse results.
That is why computers still rely on real RAM first, and only use storage as a fallback when necessary.
Source: Reddit