...
To see the actual files on disk, open shell:cache\Content.IE5. You’ll see the following view:
You see the index.dat database file, and four randomly named subfolders each of which, if opened, contains cached response files:
The folders are randomly named to mitigate certain types of attacks that involve placing malicious content at predictable file locations and then opening it using a url that uses the file:// protocol scheme. There are four of them to similarly aid in randomness, as well as for legacy reasons (older filesystems had a limit on the number of files contained in a single folder).
The Protected Mode cache files can be viewed in a similar way, by opening shell:cache\Low\Content.IE5 instead:
Again, you’ll see the same layout, with four more randomly named subfolders.