Many informal blog articles are on the "memory capacity of the human brain" in bytes. but this question is flawed because people forget things all the time.

A more well-defined question is, what is a reasonable lower bound on the number of bytes necessary to describe the state of a normal human brain?

Describing the connectome might be enough. the connectome is 100-1000 trillion synapses, but it's unclear how many bytes would be needed to describe the state of each synapse, since synapses have different configurations of things like "calcium channels". Chemical and electircal synampses, etc.

If we assume that each synapse can be full described by 10 64-bit floating point numbers, that's 80 bytes per synapse. And to represent the exact x-y-z position of each synapse precise to a single nanometre would require about 30 bits x 3 = 90 bits = about 11 bytes. So perhaps 100 bytes per synapse.

So that's 10k-100k trillion bytes, or 10-100 petabytes of data.

Another way to look at this is 30 years of 8K video takes up 36 GB / hour x 8760 hours / year x 30 years = 10 million gigabytes = 10 petabytes, which actually matches up quite nicely.

However, since we forget so so much, surely we remember far, far, less than this, by orders of magnitude. Perhaps it could be compressed down to 10-500 TB.

This is addressed in qntm's short story, Lena, which claims the first upload required 900,000 terabytes, which was later improved to just 6 terabytes lossless and ~1 terabyte lossy. This seems basically correct to me, but the compressed versions might be a bit too ambitious. Maybe more like 60-600 terabytes.