Atari TT030
The Atari TT030 is a member of the Atari ST family, released in 1990. It was originally intended to be a high-end Unix workstation, but Atari took two years to release a port of Unix SVR4 for the TT, which prevented the TT from ever being seriously considered in its intended market. In 1992, the TT was replaced by the Atari Falcon, a low-cost consumer-oriented machine with greatly improved graphics and sound capability, but with a slower and severely bottle-necked CPU. The Falcon possesses only a fraction of the TT's raw CPU performance. Though well priced for a workstation machine, the TT's high cost kept it mostly out of reach of the existing Atari ST market until after the TT was discontinued and sold at discount. The nascent open source movement eventually filled the void. Thanks to open hardware documentation, the Atari TT, along with the Amiga and Atari Falcon, were the first non-Intel machines to have Linux ported to them, though this work did not stabilize until after the TT had already been discontinued by Atari. By 1995 NetBSD had also been ported to the Atari TT. History

Atari Corporation realized that to remain competitive as a computer manufacturer, they needed to begin taking steps to exploit the power offered by more advanced processors in the Motorola 68000 series. At that time, the highest performance member was the 68020. It is the first true "thirty-two bit bus/thirty-two bit instruction" chip from Motorola. Unlike the 68000 used in the original STs, the 68020 is capable of fetching a 32-bit value in one memory cycle, while the older STs need two cycles. The TT was initially designed around the 68020 CPU, but as the project progressed, Atari Corp. realized that the 68020 was not the best option for the TT. The 68020 still lacked some features offered by the next successor in the 68000 line, the new 68030. The new 68030 features built-in memory-management hardware that provide separate Supervisor, User, Program, and Data virtual memory spaces, and provides a 256-byte on-chip data cache. When the decision was made to switch from a 68020 to a 68030 CPU, it presented a whole new set of problems. The original specifications for the TT's clock speed was 16 MHz, which was selected to maintain backward compatibility. The existing ST chips used in the TT (DMA and video chips for example) cannot handle anything over 16 MHz. Some software also has problems running at faster speeds. To make the system work with a 32 MHz 68030, Atari Corp. had to scale back their plans somewhat, and add a large amount of cache to the system. As a result, the processor runs at 32 MHz, while the system bus runs at 16 MHz. This is similar to the tactic employed by Apple with the ill-fated Macintosh IIvx and later employed by makers of PCs with an Intel 80486DX2 CPU which runs at double that of the system bus speed. TOS 3.01 is the operating system that Atari bundled with the TT. It is a 512 KB ROM specifically designed for the TT. However, it does not feature pre-emptive multitasking. Another variant, known as TT/X, uses Unix System V R4 and WISH (Motif extension). The TT030 was first introduced at CeBIT in Hannover, Germany and launched in 1990. It retailed for $2995 with 2 MB RAM and a 50 MB hard drive. The US release came the following year. In 1993, Atari Corp.'s exit from the computer business marked the end of the TT, as well as the entire ST family. A number of TT machines were built as developer systems for the Jaguar. Details
The TT features a number of devices that had previously been unavailable for Atari Corp. systems. For example, an AppleTalk network port (there never was a driver for it, possibly due to license problems), VME expansion bus, new VGA video graphics modes, and a true SCSI port. Existing ST features such as MIDI ports, a cartridge port, and the ASCI/DMA port are retained in this system. One device that is left out is the BLiTTER graphics chip, which first appeared in the Atari Mega ST systems four to five years earlier. Using the existing 8MHz chip would have only served to bottleneck the TT's performance. To be useful, a new 32MHz blitter chip would have had to have been designed for the TT, however Atari chose not to do so. An Atari Corp. version of Unix System V was not released until mid-1992. By the end of that year, Atari Corp. dropped all Unix development. A special version of the TT, the TT/X, was supplied with UNIX System V R4 and WISH (an extension of OSF Motif), as well as a collection of free software utilities including GCC. In the boot screen for "Atari System V", as the manual calls it, the operating system's kernel identifies itself as "UniSoft UNIX (R) System V Release 4.0. Technical specifications 
All TTs are made up of both custom and commercial chips:

Custom chips
TT Shifter "TT Video shift register chip" — Enables bitmap graphics. Features a 64-bit wide bus with interleaved access to ("dual purpose") system memory and on-chip buffers for high bandwidths. Contiguous 32 KB memory for ST modes, 154 KB for TT modes. TT GLU "Generalized Logic Unit" — Control logic for the system used to connect the STs chips. Not part of the data path, but needed to bridge chips with each other. Used in TT and MEGA STE. DMA "Direct Memory Access" — Three independent channels, one for floppy and hard drive data transfers, one for the SCSI port and one for 85C30 SCC network port. Direct access to ("dual purpose") system memory in the ST. 2 chips used. MCU "Memory Control Unit" — For system RAM. Support chips
MC6850P ACIA "Asynchronous Common Interface Adapter" — Enables the ST to directly communicate with MIDI devices and keyboard (2 chips used). 31.25 kilobaud for MIDI, 7812.5 bit/s for keyboard. MC68901 MFP "Multi Function Peripheral" — Used as an interrupt controller, timers and RS232C ports (2 chips used). NCR 5380 "SCSI Controller" — 8-bit asynchronous transfers up to 4 MB/s. WD-1772-PH "Western Digital Floppy Disk Controller" — Floppy controller chip. Zilog 85C30 SCC "Zilog Serial Communications Controller" — Two high-speed SDLC serial ports. YM2149F PSG "Programmable Sound Generator" — Provides 3-voice sound synthesis, also used for floppy signalling and printer port. HD6301V1 "Hitachi keyboard processor" — Used for keyboard scanning and mouse/joystick ports. MC146818A "Motorola Real Time Clock"
CPU: Motorola 68030 @ 32 MHz (system bus @ 16 MHz)
FPU: Motorola 68882 @ 32 MHz
RAM:
System RAM ("dual purpose") 2 MB ST RAM expandable to 10 MB
TT RAM ("single purpose") expandable to 256 MB TT RAM on daughter board using either 30-pin or 72-pin SIMMs
Sound: Yamaha YM2149 + Stereo DMA 8-bit PCM, same as in the STe
Drive: 1.44 MB (later version) or 720 KB (first TT version) 3½" floppy disk drive
Ports:
 MIDI In/Out
3 x RS-232
 Serial LAN RS-422
 Printer
 VGA Monitor (analog RGB and Mono)
 Extra Disk drive port
 ACSI and SCSI port
 VMEbus inside case
 Cartridge (128 KB)
 Keyboard (detachable)
 Joystick and Mouse ports (on keyboard)
Operating System:
 Atari's TOS with the Graphics Environment Manager (GEM) graphical user interface (GUI) TOS versions: 3.01, 3.05 or 3.06 in ROM. Four socketed 1 Mb ROMs providing 512 KB of ROM space. MiNT
 MagiC
 Atari System V
 NetBSD
Display modes:
Color: 320×200 (16 color), 320×480 (256 colors or 256 greyscales), 640×200 (4 colors), 640×480 (16 colors), palette of 4096 colors
Duochrome: 640×400 (2 colors)
Monochrome: 1280×960 mono TT high with ECL 19 in (483 mm) TTM195 monitor
Character set: Atari ST character set, based on codepage 437. Case: Two-piece desktop-style. Release Date: 1990-1991

The (at least) two versions of the TT can be distinguished by:

Internal sheet plate (old) or coating (new) for electromagnetic compatibility
CPU and FPU on daughter board (old) or directly on main board (new)
1.44 MB HD floppy drive (720 KB DD floppy drive on older models)

Emulation 

Hatari is able to emulate an Atari TT on a variety of different OS's using the SDL library. Atari Coldfire Project - Atari computer clone

References

External links
Guillaume Tello's WEB page What to do with a TT? Some hardware expansions detailed
Download page Programs for Atari, mostly for the TT. ASV Archive page Atari System V unofficial webpage. 68k-based computers
68000-based home computers
Atari ST
Computer workstations