Why can’t you buy external ram that plugs into a usb like you can for an ssd?


Why can’t you buy external ram that plugs into a usb like you can for an ssd?

In: Engineering

No, USB isn’t fast enough to make viable RAM access technology.

You can always just hook up a SSD and tell the OS to place a page file on it.

Problem is that even the fastest internal SSDs are FAR slower than RAM. The OS knows this and strategically handles moving data to/from a page file in what it thinks will be the most optimal way.

USB just adds even more steps between the drive and RAM, so I don’t think Windows even allows this anymore.

The whole purpose of ram is to have a verry fast storage to temporarily store data that’s currently needed. Usb does not have anywhere near the transfer speeds needed to serve as ram

RAM has to be very fast to access. This is why it is mounted directly on the motherboard. Any of the external ports are inherently slower because they are dynamic.

No port on your computer is fast enough to make that work well.

The point of RAM is that it is extremely fast even though it is low density, it is orders of magnitude faster than an SSD and several orders of magnitude faster than a hard drive.

RAM can be accessed in tens of nanoseconds, SSDs take up to 100 us (~1000x longer), and HDDs take 10 ms (100x longer than SSDs)

Then you’ve got to deal with bandwidth. A DDR4-3200 RAM stick can transfer 25.6 GB/s, while the maximum bandwidth for DisplayPort using all 4 lanes is just 9.6 GB/s. That’s the fastest external port you have on a computer and it has only half the bandwidth of your CPU’s connection to a single RAM stick, plus a lot of overhead in the process so it’d raise your access times to the tens of microseconds range making it a very expensive and low density SSD.

RAM only works because it is right next to the CPU with a couple hundred little signal wires running right to it, you simply cannot get the performance required over a longer range.