Meta reuses old RAM in new servers with custom bridge chip

With the cost of new RAM soaring, Meta has found a thrifty way to reuse older memory in newer servers.

The performance of about 40% of Meta’s millions of servers is limited by a lack of memory, the company said — but it has a surplus of older DIMMs from decommissioned servers, because RAM chips can last about twice as long as the rest of the machine.

To profit from this imbalance, it developed a custom Computer Express Link (CXL) chip it calls Vistara, and associated software, to decouple older memory from server memory channels, enabling its reuse in new machines alongside their native memory. Using the older RAM with the CXL interface doesn’t significantly affect performance — although it would have done if the older DIMMs were plugged straight into newer servers.