Windows 3.0 - System Requirements - Memory Modes

Memory Modes

Windows 3.0 was the only version of Windows that could be run in three different memory modes:

• Real mode, intended for older computers with a CPU below Intel 80286, and corresponding to its real mode;
• Standard mode, intended for computers with an 80286 processor, and corresponding to its protected mode;
• 386 Enhanced mode, intended for newer computers with an Intel 80386 processor or above, and corresponding to its protected mode and virtual 8086 mode.

Real mode primarily existed as a way to run Windows 2.x applications. It was removed in Windows 3.1x. Almost all applications designed for Windows 3.0 had to be run in standard or 386 enhanced modes (Microsoft Word 1.x however runs in real mode). However, it was necessary to load Windows 3.0 in real mode to run SWAPFILE.EXE, which allowed users to change virtual memory settings. Officially, Microsoft stated that an 8Mhz turbo 8086 was the minimum CPU needed to run Windows 3.0. It can be run on 4.77Mhz 8088 machines, but performance is so slow as to render the OS almost unusable. Up to 4MB of EMS memory is supported in real mode.

Standard mode was used most often as its requirements were more in-line with an average PC of that era – a 286 processor with at least 1MB of memory. Incidentally, not all 286 and 386 computers remapped memory between 640 KB (the upper limit of Conventional memory) and 1 MB as extended memory — some did not show memory between 640 KB and 1 MB at all — so on some systems with 1 MB of RAM, there is no extended memory and memory was limited to 640 KB. On such a system, Windows was limited to real mode. Many 386 computers ran Windows 3.0 in standard mode due to a lack of memory and also for performance reasons.

386 Enhanced mode was a 32-bit virtual machine that ran a copy of 16-bit Standard mode, and multiple copies of MS-DOS in virtual 8086 mode. In 286 mode, the CPU temporarily switches back into real mode when a DOS application is run, thus they cannot be windowed or switched into the background, and all Windows processes are suspended while the DOS application is in use. 386 enhanced mode by comparison uses virtual 8086 mode to allow multiple DOS programs to run (each DOS session takes 1MB of memory) along with being windowed and allowing multitasking to continue. Virtual memory support allows the user to employ the hard disk as a temporary storage space if applications use more memory than exists in the system.