Why can’t we just use SSDs with 128GB as RAM on our Computers? It seems way better than 8 or 16 GB.
In: Technology
Speed and reliability.
Ssd are a lot slower than ram, so your computer would definitely slow down a lot, also ssds degrade over time if you write to them a lot which will happen if you use them as ram, also ram is volatile memory, meaning it looses all the data if it has no power, this seems bad, but it’s also good: if something goes wrong, you can just turn the computer off and back on again and the ram will be reset, you would either need additional checks so that data that remains on it won’t cause problems if you reboot the computer
Also adding memory doesn’t necessarily make you computer faster, 16 GB is plenty enough for most people, maybe too much for the average user, however there are application where more is needed
We do, kind of. There’s different levels of memory a computer has access too.
Registers: Smallest capacity, fastest memory that the CPU uses to actually manipulate code.
Cache: Small capacity, fast memory located on the CPU itself that is used to store section of code that it’s currently working on.
System DRAM (dynamic random access memory): Medium capacity, medium speed memory that a computer stores the entire programs that are currently running. When the CPU needs some of that code, it fetches it from the RAM then adds it to the cache memory.
Virtual Memory: Large capacity, slowest memory located on a hard disk or SSD, that acts as an extension to RAM should System RAM not be enough.
SSDs, while much faster than hard drives, are still a lot slower than any other type of RAM. And while they’re both made up of integrated circuits of transistors, SSDs and DRAM have a vastly different design from one another.
Due to the way they retain data without being powered, SSDs will actually wear out over repeated write cycles. Which can be anywhere from a few hundred to a few thousand writes depending on the design used. SSD controllers utilize algorithms to spread wear evenly across the entire drive, but they will fail eventually. DRAM, meanwhile, does not wear out with repeated writes. So while you would get more capacity going this route, it would work out to be a lot slower, but much more expensive in the long run as you had to keep replacing drives.
Type | Data transfer rate
—|—
SATA SSD | 0.5GB/s
NVMe SSD (PCIe x3) | ~3GB/S
DDR4 3200 RAM | 25.6GB/s
DDR5 6400 RAM (next gen, in development) | >50GB/s
The issue with that idea is fairly evident from these numbers.
SSD’s are considerably slower than RAM when it comes to data transmission.
The fastest SSD can transfer data at about 2.3gbps, the fastest ram currently transfers data at around 45gbps
Because they’re not fast enough to act as RAM. Also, you can easily fit way more than 8 or 16GB in there. Personally, I’m sitting on 32GB, and have done so since 2013.
Compared to RAM, SSDs are much slower, have much greater latency, and have extremely limited endurance.
A block on a consumer SSD can be erased just a few thousand times (exact number depends on the SSD). RAM contents change constantly, easily millions of times a second. While SSDs can take their normal load that’s just because writes to disk are very rare comparatively speaking. The amount of stuff going on in the RAM is just brutal by comparison, and so at most a SSD can be used as swap space — to offload stuff that doesn’t need to be in RAM right now, but that might be needed later. Even then, one needs to be somewhat careful with that.
Ok so to answer your question: SSDs are alot slower (especially latency) than ram and ssd speeds are just not enough for it to be responsive enough. Plus you don’t really need that much ram. And to address the capacity question: I’ve been using 128GB RAM for 2 years, recently switched to 64GB because I never need more than 50 or so (you’ll never use that much if you just do normal stuff on your pc)
RAM is much faster to access than even solid state flash storage. We are talking like 1000 times faster. But the downside of this speed is that this kind of storage cannot retain its stored data without a constant supply of electricity, which means if that was all we had then your entire computer would be wiped (including the operating system) as soon as you turned it off.
While the capacity of RAM and hard drives are measured in the same units because they both store data, they are fundamentally different in their capabilities which is why they are used for different things.
Others have already mentioned the data transfer speed difference. But that matters only when you are moving largeish amounts of data.
But the processor needs to access data constantly as it does processing. But this data is very small. For example a single number.
So accessing data fast is very important.
On SSD acces time is some millisecond (google says 5-10 ms).
On RAM acces time is some tens of nanoseconds.
One mllisecond is 1000000 nanoseconds. It takes almost million times longer to taccess data on SSD compared to RAM
The name RAM stands for Random Access Memory. Being able to quicly access any part of the memory is important enough property that the thing was named after it.
* they are too slow to be used effectively as primary RAM
* they degrade over time, and RAM just has too much thrashing
* if you have an SSD drive, it is already being used to create virtual memory for your RAM
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