Uncovering Windows’ Hidden moricons.dll: A Journey into Early Icon Archives

Background

In every Windows installation, from the original Windows 3.0 release to the current Windows 11, the system directory contains a 12 KB DLL named moricons.dll . The file was intended to store a collection of icons used by the Program Manager, the graphical shell that preceded the modern Start menu. The original name “moreicons.dll” was truncated to “moricons.dll” to satisfy the DOS 8.3 filename limitation.

Contents of the DLL

Each icon stored in moricons.dll has a corresponding textual description in the APPS.INF file that shipped with Windows 3.0. The INF entries specify the icon resource identifier, the associated program name, and the intended use within the Program Manager.

Discovery and extraction

Engineer Stephen Kitt examined the Windows 3.0 distribution and identified the one‑to‑one relationship between the icons in moricons.dll and the entries in APPS.INF. Motivated by his findings, an anonymous contributor wrote a Python script that performs the following steps:

Loads moricons.dll as a resource library.

Enumerates all icon resources and extracts each as a separate image file (typically .ico or .png).

Parses APPS.INF to obtain the textual description for each icon identifier.

Generates a combined visual‑text table that pairs each extracted icon with its description.

The script can be invoked from a command prompt, for example:

python extract_moricons.py --dll "%SystemRoot%\System32\moricons.dll" --inf "APPS.INF" --out icons_table.html

Running the script produces an HTML document that lists every legacy icon alongside the program name and purpose recorded in the INF file.

Compatibility rationale

Microsoft senior developer Raymond Chen has explained that retaining moricons.dll costs only about 12 KB of disk space while eliminating any risk of breaking legacy applications that still reference the file. Consequently, the DLL has been shipped unchanged in every Windows release.

Significance for computer archaeology

Although the low‑resolution icons are of little practical use today, moricons.dll provides a concrete snapshot of the software ecosystem that existed during the transition from pure DOS programs to the first graphical Windows environment. By extracting and examining the icons, researchers can gain insight into the visual language, naming conventions, and program distribution of the early 1990s PC era.