CUTTING CORNERS: Faced with rising memory costs, Meta says it is reusing old DDR4 RAM in its servers rather than buying new hardware. The company revealed this week that it is repurposing DDR4 memory from decommissioned servers into its new DDR5-only machines, using a custom CXL ASIC that avoids the compatibility issues and major latency penalties that typically come with mixing memory generations. The design reportedly cuts AI inference server count by up to 25% and reduces job-restart and fragmentation overhead by 33%.
Documents presented by Meta at ISCA 2026 this week reveal that its new "MemServers" are powered by AMD's Epyc Turin CPUs, featuring 158 cores and 316 threads.
The Turin chips technically support only DDR5 RAM, but Meta got around that limitation with a custom CXL 2.0 ASIC called "Vistara," designed to let legacy DDR4 DIMMs work seamlessly alongside DDR5 platforms.
Each MemServer packs 1 TB of combined memory, including 768 GB of DDR5-6400 local RAM and 256 GB of DDR4-2400 CXL-attached RAM connected via Vistara. Meta explained that Vistara's software stack treats the DDR4 memory as a "distinct, CPU-less NUMA node," separate from the local DDR5 DRAM nodes attached directly to the processor.
