Commenter Niels wonders when and how the registry was introduced to 16-bit Windows and how much of it carried over to Windows 95.

The 16-bit registry was extremely simple. There were just keys, no values. The only hive was HKEY_CLASSES_ROOT. All it was used for was COM objects and file associations. The registry was stored in the REG.DAT file, and its maximum size was 64KB.

It is my recollection that the registry was introduced in Windows 3.1, but Niels says it's not in a plain vanilla install, so I guess my memory is faulty.

None of the 16-bit registry code was carried over to Windows 95. Windows 95 extended the registry into kernel mode, added support for values and non-string data types, increased the maximum registry size (though if some people are to be believed, not by enough), and added a bunch of other hives, like added the HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, and the HKEY_DYN_DATA, The old 16-bit registry code was woefully inadequate for all these new requirements (especially the kernel mode part), so it was all thrown out and a brand new registry written.

In the early days of the Windows 95 registry, the in-memory signature value to identify the data structures which represent an open registry key were four bytes which corresponded to the ASCII values for the initials of the two programmers who wrote it.