What this measures
One pass each of a sequential read, a sequential write, and a typed-array copy, using the buffer size you pick. Rates are decimal megabytes per second inside this heap.
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.