Windows 3.1

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Definition of Windows 3.1 in Network Encyclopedia.

What is Windows 3.1?

Windows 3.1 is the GUI-based operating system from Microsoft that made personal computers easier and more fun to use.

Microsoft Windows went through several earlier versions, but the first widely used version was Windows 3.0, which was released in 1990 and provided users with a graphical user interface (GUI) environment that was easier to learn and use than the command-line environment of the MS-DOS operating system.

In 1992, Microsoft released Windows 3.1, which included additional enhancements and utilities. Windows 3.1 is now considered a legacy operating system and has largely been replaced by Windows 95, Windows 98, Windows NT, Windows 2000, Windows ME, Windows XP, Windows 7 and Windows 10 in homes and businesses.

Windows 3.1
Windows 3.1

Windows 3.1 unique features

Unique features of Windows 3.1 that distinguished it from earlier operating systems such as MS-DOS include the following:

  • A GUI that displays applications in separate windows that can be resized and arranged in any fashion
  • Virtual memory, a technique for swapping between RAM and disk space that increases the number of applications that can be run simultaneously
  • Customizable user interface elements, including the color scheme, fonts, arrangement of windows, and mouse settings
  • Data sharing by applications using Dynamic Data Exchange (DDE) and object linking and embedding (OLE)
  • TrueType fonts, which are displayed in WYSIWYG fashion and can be scaled to any size
  • Device independence, which makes it easier for manufacturers to write device drivers for their hardware
  • Network-aware File Manager and Print Manager utilities, which enable access to shared network drives and printers
Windows 3.1 User Interface
Windows 3.1 User Interface

How it works

Windows 3.1 is a 16-bit cooperative multitasking graphical operating system that runs on top of MS-DOS and shares some architectural similarities with MS-DOS. Windows 3.1 uses a layered architecture (see the following figure) consisting of three main components:

  • A top-layer Windows application programming interface (API) that allows software developers to write 16-bit Windows programs without needing to understand the details of how the operating system routines work internally or how device drivers are implemented and communicate with underlying hardware.
  • A middle layer consisting of Windows core components and extensions. The core components make up the kernel of the operating system and consist of three subcomponents:
    • Krnl386.exe: Handles basic operating systems such as memory management, process and thread scheduling, and file input/output (I/O) 
    • User.exe: Manages user I/O devices such as the keyboard and mouse, manages communication ports, and keeps track of Windows user interface elements such as windows, dialog boxes, icons, and menus 
    • Gdi.exe: Manages drawing screen graphics and printing The middle layer also includes extensions to the core operating system components that are supplied in the form of dynamic-link libraries (DLLs) that add extra functionality to the Windows environment, such as multimedia support and DDE. Windows DLLs make the Windows operating system environment extensible, allowing software manufacturers to add basic functionality to Windows by creating their own custom DLLs. Windows optimizes memory usage by dynamically loading only the DLLs that it needs at a given time.
Windows 3.1 Architecture
Windows 3.1 Architecture
  • A bottom layer, consisting of Windows drivers, that provides device drivers for different hardware devices managed by Windows, such as the keyboard, mouse, video display, and communication ports.

Windows 3.1 has two modes of operation:

  • Standard Mode: Does not use virtual memory and cannot multitask with MS-DOS applications. In Standard Mode, MS-DOS applications can run only full-screen. 
  • 386 Enhanced Mode: (See the following diagram.) Requires an Intel 386 or higher processor, uses virtual memory, and supports multitasking of MS-DOS applications in separate windows. This mode includes the Virtual Machine Manager (VMM), which creates and manages separate virtual machines (VMs) running on a single CPU. Each VM functions as though it has access to and control over the resources of the entire system. Windows 3.1 and all 16-bit Windows applications run in a single system VM, while each additional MS-DOS application runs in its own separate DOS VM. Virtual device drivers (VxDs) are 32-bit protected-mode DLLs that allow more than one process to share a system resource simultaneously in order to support multitasking. Windows applications are multitasked cooperatively – that is, they must be written to properly relinquish control to other applications to allow them to share system resources. Running at the MS-DOS prompt invokes the 386 Enhanced Mode system loader (win386.exe). 

Windows 3.1 stores its system and operating system configuration information in a series of text files accessed during the boot process. These include the following:

  • Config.sys and autoexec.bat, which have the same function as in MS-DOS
  • Win.ini, which configures the Windows desktop and working environment
  • System.ini, which stores the Windows system configuration, including device drivers and mode settings
  • Other INI files such as progman.ini, protocol.ini, control.ini, and lanman.ini
Windows 3.1 Virtual Memory in 386 Enhanced Mode
Windows 3.1 Virtual Memory in 386 Enhanced Mode


Windows 3.1 includes a 32-bit file system technology called FastDisk, which filters Int 13H calls to the hard disk controller and uses 32-bit protected-mode device drivers or accesses the disk through the system BIOS, depending on how it is configured. However, this feature is disabled by default when Windows 3.1 is installed; you can turn it on by using the 386 Enhanced utility in Control Panel.