Load DOS Command Processor into High Memory (Windows 95/98/Me)
DOS is limited to 640kb low memory, as more device drivers are loaded that space is used up leaving less available memory for applications. This setting loads the DOS command processor into high memory, freeing some low memory for other applications.

Increase the Number Disk Buffers (Windows 3.1/DOS)
This setting can be used to increase the number of disk buffers available to DOS.

Load Device Drivers into Memory (Windows 3.1/DOS)
This setting is used to load specified device drivers into memory (or high memory).

Control the Number of File Control Blocks (FCBs) (Windows 3.1/DOS)
This setting specifies the number of file control blocks (FCBs) that the operating system can have open at the same time.

Controls the Number of Simultaneous Files (Windows 3.1/DOS)
This setting specifies the number of files that the operating system can access at one time.

Specify the Maximum Number of Drive Letters (Windows 3.1/DOS)
This setting control the maximum number of drivers accessible by a drive letter.

Control the Number of Data Stacks (Windows 3.1/DOS)
Support the dynamic use of data stacks to handle hardware interrupts.

Use Extended Memory (Windows 3.1/DOS)
Himem, an extended-memory manager, is a program that coordinates the use of your computer's extended memory, including the high memory area (HMA). It must be loaded before any application or device drivers can use extended memory.

Enable the Ability to Load Devices into Upper Memory (Windows 3.1/DOS)
Originally EMM386 was required to provide EMS memory, an alternate form of extended memory. Now with the sparse use of EMS, it's primary purpose is to provide support for loading real-mode device drivers in the upper memory area.