Typically, vector databases store the index in memory, requiring machines with a lot of RAM. There are ways to reduce the memory usage, e.g. with quantization,

Typically, vector databases store the index in memory, requiring machines with a lot of RAM. There are ways to reduce the memory usage, e.g. with quantization, but more recently disk-first databases (LanceDB) and algorithms (DiskANN) are becoming more popular as they scale better and are cheaper.