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Motivation

When using npm or Yarn, if you have 100 projects using a dependency, you will have 100 copies of that dependency saved on disk. This is caused by the use of a flat node_modules structure. However, with pnpm, the dependency will be stored in a content-addressable store, so:

1. If you depend on different versions of the dependency, only the files that differ are added to the store. For instance, if it has 100 files, and a new version has a change in only one of those files, pnpm update will only add 1 new file to the store, instead of cloning the entire dependency just for the singular change.
2. All the files are saved in a single place on the disk. When packages are installed, their files are hard-linked from that single place, consuming no additional disk space. This allows you to share dependencies of the same version across projects.

As a result, you save a lot of space on your disk proportional to the number of projects and dependencies, 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, and our corresponding documentation about the content-addressable store:

• Flat node_modules is not the only way
• Symlinked node_modules structure