In-core algorithms require the entire array(s) in main memory to perform some computation. Out-of-core algorithms are typically block-based and stream the array

In-core algorithms require the entire array(s) in main memory to perform some computation. Out-of-core algorithms are typically block-based and stream the array blocks from persistent storage to main memory on demand, working on parts of the array(s) at a time, thus minimizing the memory requirements. If this is done asynchronously and carefully, for some CPU-bound algorithms you may be able to completely hide the storage-to-memory cost, thus saving memory without losing performance.