QD1

Queue depth is how many requests a program has waiting on the drive at once. At QD1 it sends one, waits for the answer, then sends the next, so the result is set by latency: how long a single request takes. At high queue depths, such as the QD32 figures spec sheets often print, the drive works on many requests in parallel and reports a far larger number of operations per second.

That is why headline random read figures overstate what most people feel. Opening an application, loading a game level or reading small files is mostly a short chain of dependent requests, closer to QD1 than to QD32. Two drives with very different high-queue-depth ratings can be close at QD1, and a drive with a good QD1 random read tends to feel quick in daily use. Few makers print a QD1 figure at all.

A browser reads a file one request at a time, so the browser storage test's random read is nearest in kind to a QD1 figure, though still with a file system and a browser in the way. It is not a raw-drive number and should not be compared to a spec sheet as if it were. The SSD spec sheet page shows which makers print QD1 random reads.