cache: centralize concept explanation in tooltip

content/docs/command-reference/add.md

@@ -76,10 +76,10 @@ A `dvc add` target can be either a file or a directory. In the latter case, a
 `.dvc` file is created for the top of the hierarchy (with default name
 `<dir_name>.dvc`).
 
-Every file inside is stored in the cache (unless the `--no-commit` option is
-used), but DVC does not produce individual `.dvc` files for each file in the
-entire tree. Instead, the single `.dvc` file references a special JSON file in
-the cache (with `.dir` extension), that in turn points to the added files.
+Every file in the dir is cached normally (unless the `--no-commit` option is
+used), but DVC does not produce individual `.dvc` files for each one. Instead,
+the single `.dvc` file references a special JSON file in the cache (with `.dir`
+extension), that in turn points to the added files.
 
 > Refer to
 > [Structure of cache directory](/doc/user-guide/dvc-files-and-directories#structure-of-the-cache-directory)

content/docs/command-reference/cache/index.md

@@ -15,15 +15,12 @@ positional arguments:
 
 ## Description
 
-The DVC Cache is where your data files, models, etc. (anything you want to
-version with DVC) are actually stored. The data files and directories visible in
-the <abbr>workspace</abbr> are links\* to (or copies of) the ones in cache.
-Learn more about it's
-[structure](/doc/user-guide/dvc-files-and-directories#structure-of-the-cache-directory).
+Tracked files and directories visible in the <abbr>workspace</abbr> are links\*
+to the ones in the project's <abbr>cache</abbr>.
 
-> \* Refer to
+> \* Or copies. Refer to
 > [File link types](/doc/user-guide/large-dataset-optimization#file-link-types-for-the-dvc-cache)
-> for more information on file links on different platforms.
+> for more information on supported linking on different platforms.
 
 For cache configuration options, refer to `dvc config cache`.
 

content/docs/command-reference/config.md

@@ -131,11 +131,8 @@ remote. See `dvc remote` for more information.
 
 ### cache
 
-A DVC project <abbr>cache</abbr> is the hidden storage (by default located in
-the `.dvc/cache` directory) for files that are tracked by DVC, and their
-different versions. (See `dvc cache` and
-[DVC Files and Directories](/doc/user-guide/dvc-files-and-directories#structure-of-the-cache-directory)
-for more details.) This section contains the following options:
+This section contains the following options, which affect the project's
+<abbr>cache</abbr>:
 
 - `cache.dir` - set/unset cache directory location. A correct value is either an
   absolute path, or a path **relative to the config file location**. The default

content/docs/user-guide/basic-concepts/dvc-cache.md

@@ -3,7 +3,7 @@ name: 'DVC Cache'
 match: ['DVC cache', cache, caches, cached, 'cache directory']
 ---
 
-The DVC cache is a hidden storage (by default located in the `.dvc/cache`
-directory) for files that are tracked by DVC, and their different versions.
-Learn more about it's
+The DVC cache is a hidden storage (by default in `.dvc/cache`) for files and
+directories tracked by DVC, and their different versions. Data is cached into a
+special flattened
 [structure](/doc/user-guide/dvc-files-and-directories#structure-of-the-cache-directory).

content/docs/user-guide/dvc-files-and-directories.md

@@ -256,7 +256,7 @@ Full <abbr>parameters</abbr> (key and value) are listed separately under
 - `.dvc/cache`: The <abbr>cache</abbr> directory will store your data in a
   special [structure](#structure-of-the-cache-directory). The data files and
   directories in the <abbr>workspace</abbr> will only contain links to the data
-  files in the cache. (Refer to
+  files in the cache (refer to
   [Large Dataset Optimization](/doc/user-guide/large-dataset-optimization). See
   `dvc config cache` for related configuration options.
 
@@ -297,13 +297,17 @@ Full <abbr>parameters</abbr> (key and value) are listed separately under
 
 ## Structure of the cache directory
 
-The DVC cache is a
+The DVC cache is a hidden
 [content-addressable storage](https://en.wikipedia.org/wiki/Content-addressable_storage)
-(by default in `.dvc/cache`), which adds a layer of indirection between code and
+(by default in `.dvc/cache`). It adds a layer of indirection between code and
 data.
 
-There are two ways in which the data is <abbr>cached</abbr>: As a single file
-(eg. `data.csv`), or as a directory.
+There are two ways in which the data is <abbr>cached</abbr>, depending on
+whether it's a single file, or a directory (which may contain multiple files).
+
+Note files are renamed, reorganized, and directory trees are flattened in the
+cache, which always has exactly one depth level with 2-character directories
+(based on hashes of the data contents, as explained next).
 
 ### Files
 
@@ -331,9 +335,7 @@ data/images/
 $ dvc add data/images
 ```
 
-The directory is cached as a JSON file with `.dir` extension. The files it
-contains are stored in the cache regularly, as explained earlier. It looks like
-this:
+The resulting cache dir looks like this:
 
 ```dvc
 .dvc/cache/
@@ -345,13 +347,14 @@ this:
     └── 0b40427ee0998e9802335d98f08cd98f
 ```
 
-The `.dir` file contains the mapping of files in `data/images` (as a JSON
-array), including their hash values:
+The files in the directory are cached normally. The directory itself gets a
+similar entry, which with the `.dir` extension. It contains the mapping of files
+inside (as a JSON array), identified by their hash values:
 
 ```dvc
 $ cat .dvc/cache/19/6a322c107c2572335158503c64bfba.dir
 [{"md5": "dff70c0392d7d386c39a23c64fcc0376", "relpath": "cat.jpeg"},
 {"md5": "29a6c8271c0c8fbf75d3b97aecee589f", "relpath": "index.jpeg"}]
 ```
 
-That's how DVC knows that the other two cached files belong in the directory.
+That's how DVC knows that those two cached files belong in the directory.

content/docs/user-guide/large-dataset-optimization.md

@@ -1,12 +1,7 @@
 # Large Dataset Optimization
 
-In order to track the data files and directories added with `dvc add` or
-`dvc run`, DVC moves all these files to the <abbr>cache</abbr>. A
-<abbr>project</abbr>'s cache is the hidden storage (by default located in
-`.dvc/cache`) for files that are tracked by DVC, and their different versions.
-(See `dvc cache` and
-[DVC Files and Directories](/doc/user-guide/dvc-files-and-directories) for more
-details.)
+In order to track the data files and directories added with `dvc add`,
+`dvc repro`, etc. DVC moves all these files to the project's <abbr>cache</abbr>.
 
 However, the versions of the tracked files that
 [match the current code](/doc/tutorials/get-started/data-pipelines) are also