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Motivation

pnpm uses a content-addressable filesystem to store all files from all module directories on a disk. When using npm or Yarn, if you have 100 projects using lodash, you will have 100 copies of lodash on disk. With pnpm, lodash will be stored in a content-addressable storage, so:

1. If you depend on different versions of lodash, only the files that differ are added to the store. If lodash has 100 files, and a new version has a change only in one of those files, pnpm update will only add 1 new file to the storage.
2. All the files are saved in a single place on the disk. When packages are installed, their files are linked from that single place consuming no additional disk space. Linking is performed using either hard-links or reflinks (copy-on-write).

As a result, you save gigabytes of space on your disk and you have a lot faster installations! If you'd like more details about the unique node_modules structure that pnpm creates and why it works fine with the Node.js ecosystem, read this small article: Flat node_modules is not the only way.