Can multiple Colab notebooks share the same Runtime?

Question

In Q1 2019, I ran some experiments and I noticed that Colab notebooks with the same Runtime type (None/GPU/TPU) would always share the same Runtime (i.e., the same VM). For example, I could write a file to disk in one Colab notebook and read it in another Colab notebook, as long as both notebooks had the same Runtime type.

However, I tried again today (October 2019) and it now seems that each Colab notebook gets its own dedicated Runtime.

My questions are:

• When did this change happen? Was this change announced anywhere?
• Is this always true now? Will Runtimes sometimes be shared and sometimes not?
• What is the recommended way to communicate between two Colab notebooks? I'm guessing Google Drive?

Thanks

Answer 1

Distinct notebooks are indeed isolated from one another. Isolation isn't configurable.

For file sharing, I think you're right that Drive is the best bet as described in the docs: https://colab.research.google.com/notebooks/io.ipynb#scrollTo=u22w3BFiOveA