What this measures
The average of a read pass and a copy pass at the size you choose. Calling it bandwidth is an estimate of those two loops, not a measured memory-bus width.
How to read it
Rates use decimal megabytes (1,000,000 bytes) per second. Change the buffer size if you want a longer loop. A number that swings between runs belongs on the stability page.
What it cannot do
A successful allocation is not a clean bill of health for the RAM sticks. The browser can refuse a large buffer while plenty of memory is installed. Nothing here walks the full address space.
Questions
Is this a RAM fault test?
No. It never walks the whole memory looking for bad bits. A failure to allocate is a browser limit.
Why is deviceMemory only 8?
The API returns coarse buckets. 8 means about 8 GB or more, and many browsers hide the field.
Why do read and copy disagree?
They are different loops. A bulk copy can use a faster path than adding up every element.