.theinquirer.net/inquirer/news/2203736/chinese-chip-upstart-aims-to-take-down-intel-with-longson-refresh

Biggest improvement: "The new version of the processor is not only a die shrink, but also includes a new L3 cache. The original version of the Longson 3B chip had a 256KB L2 cache for each core. This was originally thought to be enough for a decent performance, but according to Chen, real life showed that there were too many cache misses that resulted in a performance penalty, as data had to be loaded from main memory.
Therefore the 32nm version includes a shared 8MB L3 cache.

The Inquirer "

That's the cause why they don't sell the original Loongson 3B to customers because the the chip was to hott 50watt TDP and it was to slow to many cache fails.

i checked about a 3b main board in the past after the European seller told me the main-boards are in stock but i get this answer after he checked it in the headquarters :

"After checking with the headquarters, unfortunately the 3B serial main boards are not available for sell, they are wondering if you can take 3A serial main boards?

Best regards,

Eileen Zhang info@tekmote.nl "

Now we know why the 65nm 3B without L3 cache is just a internal sample and the one for customers are the 32nm 3b with 8mb cache.