MESS currently supports for the Mega STe both cart dumps and disk images. The former are accepted in .stc format and use the “cartridge” (cart) device; the latter are accepted in .st format and use one of the two floppy drives, “floppydisk1” (flop1) and “floppydisk2” (flop2).
Also notice that the “printer” (prin) and the two serial ports, “serial1” (serl1) and “serial2” (serl2), are emulated as well.
This system requires full keyboard emulation to work correctly. At startup, full keyboard emulation mode is enabled by default. Whilst in full keyboard emulation mode, some key associated functionality may be disabled (like the ESC key for EXIT). The keyboard emulation mode is toggled using the “Scroll Lock” key (by default).
Different RAM configurations are possible for the megaste in MESS. You can switch between them, changing the -ramsize parameter. At command line, you simply have to add -ramsize ram_value, where ram_value can assume one of the following values
1m - to emulate a Mega STe 1 2m - to emulate a Mega STe 2 4m (default) - to emulate a Mega STe 4
The emulation of this system is Preliminary.
The Atari Mega STe is the successor of the Atari Mega ST. It is an Atari STe with some features of the TT (the case, the VME bus) and has a new version of TOS (2.05 and 2.06).
It has (like the Mega STf) a battery-backed up clock. The user can choose in the configuration panel the speed of the CPU (8 or 16 MHz) and can switch on or off a small memory cache. Thanks to these two features, the Mega STe was really faster than the STf.
Some companies developed VME graphic cards for the Mega STe. This computer had less success than the Mega STf and was used as a publishing station or in music studios.
A minor note: the Mega and TT gave a nod to the earlier integrated-keyboard ST series by adding a tongue-and-groove design element for loosely connecting the keyboard to the base of the CPU.
The Mega STe ended production in 1993. This was also the only Atari product every to have an Appletalk networking port built-in. Some models included hard drives, and some did not. The drives were usually shipped separately to the the dealers, and installed in the store. The hard drive, a regular IDE drive (instead of the earlier ST models which used a SCSI-to-DMA interface board in the drive casing).
(info from old-computers.com)