by Atari Explorer Technical Staff
Atari Explorer Magazine
© 1991 Atari Corp.

• A Bit of History
• The TT030
• The All-American TT
• Fast RAM, and Faster!
• TT Video
• I/O and Networking
• SCSI Support
• Other System Facilities
• System Software
• The TT Upshot

    Currently selling well in European markets, the TT represents a big step forward in Atari's race to stay on the leading edge of affordable personal computer and workstation technology. Four years in the planning, it represents the present culmination of Atari's desire to present business and the mass-market with a complete, vertically-integrated line of computing systems for every application. Sam Tramiel, Atari's President, has spoken of the TT in this context. "Atari equipment now covers the whole spectrum, providing platforms for home computing and entertainment, to small-business word-processing and basic productivity, through single-user executive workstation and DTP, and now, with the TT, into high-end desktop-publishing, CAD/CAE, presentation and video graphics, multiuser applications, and networking."

    Atari Explorer's Technical Staff has recently been permitted to go hands-on with the latest, greatest revision of the proposed American TT. Helping us with our research have been Leonard Tramiel, Atari's V.P. of Software Development, and Terrea Thompson, arguably one of the most knowledgeable people in the world on the subject of the Atari TT from the user's perspective, and author of major sections of the TT's English-language manual.

A Bit of History

The name of the Atari ST derives from the nature of its microprocessor, the 68000 -- a so-called "sixteen/thirty-two bit" processor (hence "ST"), by virtue of its 16-bit-wide data bus and 32-bit-wide internal registers. Though capable of exceptional performance and sporting a rich instruction set, the 68000's 16-bit-wide data path imposes certain restrictions. Most important among these, the chip cannot read a 32-bit quantity from memory in fewer than two bus cycles. Thus, although the chip's internal data registers and operations accommodate 32-bit numbers, filling them with such numbers requires twice the time it should. Moreover, most 68000 assembly-language instructions are four bytes (32 bits) in length, meaning that the processor requires two bus cycles to read the majority of steps in its own software. The 68000 also suffers somewhat from the fact that although its address registers and program counter are theoretically 32 bits wide, only 24 of these 32 bits are actually used. The chip is thus limited to addressing a total of "only" 16MB of memory.

    As early as 1986, therefore, Atari realized that it would have to begin taking steps to exploit the added power offered by successor chips in the 68000 series. At the time, the most important of these was the 68020 -- the first "thirty-two/thirty-two bit" chip -- capable of fetching a 32-bit quantity in one cycle, and of addressing four gigabytes of RAM. The first TT (from "thirty-two/thirty-two") was prototyped around this chip.

    As time went on, however, Atari realized that the 68020 was not an ideal stopping-point for the TT technology it was developing. Though powerful, the 68020 still lacked certain important features offered by the next successor in the 68000 line, the 68030. This chip features full 32/32-bit address/data bus and internal registers; separate Supervisor, User, Program, and Data virtual memory spaces; built-in memory-management hardware; and 256-byte, on-chip instruction and data caches.

    What does all this mean? In layman's terms, the 68030 can run like a bat out of hell and can directly address a huge amount of RAM: theoretically up to 4 gigabytes. Though no affordable current machine architecture would ever include this much physical memory, the 68030's memory-management hardware is capable of using hard disk space to create a usable "virtual" memory map that is indeed this large; simply by swapping program code and data "pages" in and out from disk, as required. The on-chip instruction cache allows the chip to store up to 256 bytes worth of instructions ahead of the current program counter address, decoding and executing these instructions from chip RAM instead of from main memory. Pre-fetch functions semi-concurrently with other on-chip operations, further streamlining the 68030's performance.

    Atari knew it had a winner with the 68030 architecture: a chip capable of running not only optimized versions of the ST operating system, TOS, but of cooperating with the demands of popular multitasking/multiuser operating systems such as UNIX. A machine based on the 68030 would be able to serve a wide variety of needs -- serving as an ultra-high-performance ST, while offering business, industrial, and academic users access to one of the world's most popular and best-supported operating systems. Realizing this, they decided to gamble bravely; scrapping the 68020-based TT1 architecture in favor of one more powerful, on the surmise that by the time the design was ready for production, 68030 chips would be available in quantity, at reasonable prices. The gamble, as we'll see, paid off.

The TT030

Over the next three years, several revisions of the TT architecture surfaced in Atari's R&D labs, designed around chips spec'ed between 8 and 16MHz. At the same time, Atari's Industrial Design Division, under the direction of lra Velinsky, began developing the aesthetic that would mark Atari's new top-of-the-line flagship system as unique. From the beginning, Velinsky steered away from the "gray wedge" and "gray box" aesthetics that dominate the ST line. Even very early case designs suggest the glimmerings of a more sophisticated sensibility, drawn from classical architecture.

    Over time, Velinsky's vision for the TT -- now referred to as the "TT030" -- grew more complete, informed by the demands of the Technical Division to provide space and ergonomic conveniences that had never found their way into the earlier ST designs. Space for an internal hard drive was added, expanding the case laterally by several inches. Edges were sharpened and sloped more aggressively -- ornamentation reduced to a minimum.

    Velinsky's final production designs show an ST vastly transformed: a bipartite housing (CPU/hard disk) that functions as a single desktop unit, set upon a pedestal and colored marble-white. The keyboard, an ST-compatible 94-key detachable unit with mouse connector, can be rested on the pedestal, creating the appearance of a one-piece system. The image is one of substance and cool elegance, equally at home in the design studio or the executive suite. TT monitors, currently in the final design stages, will rest on tilt-swivel pedestals that integrate with the upper surface of the TT030 housing, creating a seamless system for the desktop. A 14-inch diagonal color monitor, among other options, is planned.

    Velinsky states: "The design of the TT was driven by the desire to have each part of the system express the form of what it contains. The hard disk enclosure expresses the form of the hard drive; the floppy section the form of the floppy drive; the "connectors section," -- or pedestal slab -- isolating and emphasizing the I/O connectors it contains, and acting as a keyboard support. We wanted, and I think succeeded, in making something unique."

The All-American TT

The Atari TT030 is essentially an ST, fully back-compatible both in hardware and systems software with current ST designs. Jim Tittsler, one of Atari's lead engineers, explains that Atari went to great lengths to preserve ST compatibility in the TT. "We bent over backward, in fact." He relates. "The biggest hardware-related problem we anticipated was with current ST software, written for the 68000, that didn't handle the high bytes of addresses correctly. The manuals for the 68000 clearly state that all software that hopes to run on later versions of the chip should be sure to set the high byte of a 32-bit address to zero. But a lot of compilers and assemblers set this byte to $FF. The result was that we had to add circuitry to the TT, capable of intelligently decoding addresses, and sending them to the proper places in memory."

    The result is that a TT030 will run most ST software without modification, the exception being programs that use the high bytes of address fields in illegal ways (for example, as a type field for a pointer). Other problems may result from the use of the 68030's instruction cache, particularly with self-modifying 68000 code that doesn't know it's been read into an on-chip buffer. For this reason, the TT boots with the 68030 caches turned off, though they can be turned on, much like the Blitter on a Mega ST, with a desktop control.

    Other minor problems may result from a slight difference between 68000 and 68030 architecture: the fact that the "move from Status Register" instruction is accessible from user mode on the 68000, but privileged on the multiuser 68030. Certain compilers use this instruction, which will cause a privilege violation exception if executed from user mode on the 68030.

    To solve the hitch, Atari has incorporated a customized exception-handler in the BIOS that traps this error, replaces the offending instruction with a "move from Condition Code Register" instruction, and executes the passage again. This is said to reliably solve most problems of this kind, without significantly affecting software performance.

    The main difference between the TT030 and an ST, of course, is speed. Running flat out, a 32MHz TT030 is potentially better than eight times faster than an ST! (The developer's documentation laconically points out that ST software that employs software timing loops will not run correctly.)

    By and large, however (and Atari has spent months testing software to prove the point), the TT030 will run every major piece of ST software on the market. Moreover, software that properly follows GEM standards in addressing such facilities as the screen, will immediately be able to make use of the TT's improved graphics resolution and color palette. Software written to exploit STe-quality sound-generation hardware will find similar facilities in the TT platform. Software currently under development, of course, will be designed with the capacity to exploit all of the TT's advanced capabilities.

Fast RAM, and Faster!

There are three kinds of memory in a TT030. ST RAM is dual-purpose, shared (as in a standard ST) between the CPU and all ST devices, including video, ACSI DMA, and DMA digital sound (see below). Present versions of the TT come with 2MB of ST RAM, expandable to 4MB total, just like a Mega 4, though the final installed/expanded numbers remain a marketing decision. We note that no German TT is presently being sold with less than 4MB of RAM installed. Programs executing in ST RAM force the TT CPU to share clock cycles with video and other devices, somewhat slowing the central processor; though execution will remain significantly faster than is possible on a standard ST.

    TT RAM, by contrast, is single-purpose RAM, not shared among ST-compatible devices. TT RAM is not visible to ST devices. It is, however, visible to the TT's SCSI (Small Computer System Interface) DMA subsystem, meaning that it can be employed directly as a source or destination for hard disk (or other SCSI device) data transfers. The TT030 presently has room for one TT RAM board containing 4MB of RAM in 1Mbit chips, expandable to 16MB with 4Mbit chips, when these become available. Again, final configuration is as yet in the hands of Atari's Marketing Division.

    A third type of RAM may be installed on a board plugged into the TT's VME socket. VME-interfaced RAM is visible only to the CPU. However, use of it incurs a single wait-state per bus cycle, meaning that this RAM is somewhat faster than ST RAM, but somewhat slower than TT RAM.

    New software, written expressly for the TT, will naturally take advantage of the distinction between ST RAM and TT RAM, likely doing much of its high performance calculating in the latter, where it can enjoy full processor speed, while leaving screen data, sound data, and other I/O-bound components in the former. However, although the present generation of ST software, written before there was any concept of "slow" (ST) or "fast" (TT) RAM, is not inherently designed to take advantage of the distinction, there is a way in which much of it may be made to do so immediately without significant revision.

    Depending on what a current program is designed to do, it tends to fall into one of two categories: 1) programs that must run entirely from ST RAM, 2) programs that can execute from TT RAM but must satisfy mass data-space requests (Malloc() calls) from ST RAM. Much entertainment software, dependent as it tends to be on display and sound, falls into the former category, while a portion of productivity and other less graphics-dependent software falls into the latter. The TT's revised operating system is capable of treating programs in either way, depending on the setting of bits in the header of the program's executable disk file. There is thus hope that by changing a single byte in the program header -- something that may be done by the user with a simple utility program -- certain present-generation software may be able to take full advantage of the TT hardware, without further modification.

TT Video

The TT030 supports all of the ST's normal graphics modes (low resolution, 320 x 200, 16-colors; medium resolution, 640 x 200, 4-colors; and high resolution, 640 x 400, 2-colors), while enhancing ST monochrome so that it can employ any two colors -- not just black and white. In addition, the TT adds three new graphics modes of its own: TT low, 320 x 480, offering 256 colors (significantly exceeding the capabilities of standard IBM VGA); TT medium, 640 x 480, with 16 colors; and TT high -- a special black and white mode offering stunning 1280 x 960 resolution. This latter resolution is available only on special monitors. All the TT's color modes draw from a palette of 4,096 possible colors, as on the STe. Because of the new graphics modes, the TT's video RAM requirements have increased from the ST-standard 32K to 150K.

    New XBIOS calls have been implemented to give access to the TT's larger color-tables, while back-compatibility has been maintained with ST norms for ST video modes. In addition, AES and VDI, the Application Environment Services and Virtual Device Interface software packages that make up the bulk of GEM from the programmer's perspective, have been enhanced and will work transparently with the TT's new graphic modes. Currently-available software that has adhered rigorously to GEM programming standards (and that has used only calls to GEM (VDI) to determine system configuration) will work in the new graphics modes.

I/O and Networking

The TT030 has hardware to support a total of four serial ports. Port 1 is ST-compatible, obtained from the 68901 Multi-Function Peripheral chip. That chip also supports Port 2, which works like the ST-compatible port, except that it has only transmit, receive, and ground signals. The remaining two ports are drawn from the TT's new 8530 Serial Communications Controller, and support full handshaking. One of these ports shares hardware with the Localtalk-compatible 8-pin female mini-DIN (Deutsche Industrie Normung) LAN connector on the TT's side (see below). Thus if one elects to employ the LAN, serial Port 4 is unavailable. The BIOS has been enhanced to provide support for all these ports, including flow control. Physical serial ports themselves are of the AT-style 9-pin variety.

    This proliferation of serial ports means that it will be easy to use the TT in a variety of network-based and single-user telecommunications contexts. Hooked to modems, the serial ports can be employed to support multiple telecommunications sessions, either under the control of UNIX or special TOS-based multitasking software. The TT might be used as the telcom server on a LAN. Under UNIX, terminals can be attached to these ports, and the TT employed as a multiuser server.

    The TT's network interface facilities are impressive. As noted above, the TT comes with a Localtalk connector installed. This medium-speed, industry-standard LAN protocol is designed for file and peripheral sharing in small networks. High-speed network interfacing is provided via two routes. The TT's industry-standard VME Bus slot offers room for a single-Eurocard-sized (3U) VME-based Ethernet board; and SCSI-interfaced Ethernet units can be added via the TT's external SCSI port or internal SCSI ribbon-cable connector.

SCSI Support

The TT030 will support the industry-standard Small Computer System Interface (SCSI) completely. In hardware, the TT will ship with both a motherboard-mounted 50-pin internal SCSI connector (plus space for mounting an internal SCSI hard drive); and a 25-pin, external, Mac-compatible SCSI connector, to which up to seven SCSI devices can be daisy-chained. Atari hard disk utilities can recognize, format, partition, and render bootable, almost any standard SCSI drive. The TT's SCSI direct-memory-access subsystem can send and receive information equally well, both from ST RAM and faster TT RAM, meaning that present and future software will be able to exploit SCSI peripherals efficiently.

    The result of this level of support is that TT owners will be able to buy almost any SCSI hard drive "off the shelf," and attach it to their TT with a minimum of trouble. Other SCSI peripherals, such as streaming tape drives, 9-track tape, etc., are also "plug compatible," though device drivers for these units must be provided by a value-added-reseller or by the user.

Other System Facilities

Adding to the power of the TT030 as an engine for number-crunching, CAD/CAE, videographics, and other math-intensive applications; the machine will ship with a 68882 floating-point math coprocessor installed. The interface between the TT's 68030 CPU and the 68882 is via the 68030's "direct" routing, rather than the slower and clumsier method of peripheral I/O, such as was used in the Atari Mega ST-compatible floating-point peripheral daughterboard. The result, says Atari's Jim Tittsler, is "a vast increase in speed and simplicity of programming."

    Sound on the TT030 is via stereo DMA, just as in the STe. Left and Right audio RCA jacks are provided on the TT backplane for output to stereo amplifier. An internal speaker is also provided. Additional standard ports will include most of the hardware found on STs, including MIDI IN and OUT, a port for attaching an external floppy disk, ST-compatible mouse and joystick ports, and a cartridge port. The TT's internal floppy drive is a 720K ST-standard unit. At press time, it was also decided that TT030's would initially ship with both floppy and internal hard drives installed, though the size of these units was still an open question.

System Software

The TT030's native operating system is Atari's ST-standard TOS/GEM, an enhanced version of which is burned into the TT's ROM. According to Leonard Tramiel, Atari's V.P. of Software, the specified TT enhancements to TOS, GEM (AES/VDI), and -- in many ways most impressively and visibly -- to the desktop, took several man-years to implement. So striking are the changes to the desktop that we've elected to describe them in a separate hands-on article.

    To summarize them, briefly, the TT's windowing system has been completely, if compatibly, redesigned, being rendered faster, more colorful, and more informative. A method for adding extensions to the Control Panel has been standardized. The Control Panel itself has been updated to handle the TT's new video modes and STe-compatible audio hardware. Finally, the system by which applications are installed on the system at start-up has been completely revised.

    As an alternative to TT TOS, the TT030 is capable of running UNIX, the popular multitasking/multiuser operating system. Atari's initial UNIX product offering will be UNIX V.4, which is fully compatible with POSIX, and the X/Open Portability Guidelines. The X/Window System, one of the most popular UNIX Graphical User Interface packages, will also be provided, as will an actual graphic user interface, running on top of X/Window.

    Unlike TOS, UNIX is truly a multitasking operating system, capable of supporting numerous simultaneous processes. Single-users can employ multitasking in a variety of ways to improve productivity: ranging from maintaining multiple simultaneous telecommunications sessions, to working and printing in parallel. Task-to-task communication facilities available under UNIX make relatively simple the task of sharing information between programs. UNIX is also multiuser, meaning that the TT will potentially be capable of acting as server to several independent workstations, each with multitasking capability. UNIX offers a wide variety of facilities for insuring the safety and security of data in multiuser installations. Moreover, unlike TOS, UNIX can exploit the 68030's built-in memory-management subsystems to create large "virtual" computing environments.

    The availability of UNIX -- particularly in such a complete form -- is a significant development that may well affect the impact of the TT on business, in research, and in the academic sector. To start with, UNIX is a mature operating system that is exceptionally well-supported with software (several thousand packages are available, covering every conceivable category of application). TT UNIX adopters will thus immediately have a large library of applications on which to draw, many of which are available at low or no cost through academic and shareware distribution channels. UNIX is OS/2's major competitor for the office multitasking market, and is established as the operating system of choice in programmer training and computer science curricula, worldwide. As a UNIX platform, the affordable TT030 may leapfrog machines from IBM, Apple, NeXT, and Sun, as the best choice for mass installation of UNIX systems in these environments.

The TT Upshot

As the TT nears American release, Atari Explorer will be staying on top of developments, bringing you the first word on final production configurations and other details of the system. At the moment, however, certain things are already abundantly clear.

    First, the Atari TT constitutes a step forward in affordable, high-performance computing that is nothing short of revolutionary. Though final system prices have not yet been established, it is certain that the cost of a TT with power approximately equal to that of a Macintosh IIC or fully-loaded high-speed 80386 PC clone with VGA will cost several thousand dollars less than the former, and on the street, perhaps a thousand dollars less than the latter.

    Second, judging from the TT's architecture, which is optimized for throughput in math-intensive applications, the machine is an ideal platform for high-end desktop-publishing, computer-aided design, and computer-aided engineering applications. As such, it constitutes an ideal "top end" for the upward-compatible suite of hardware platforms Atari has fielded to serve these important vertical markets.

    Third, the availability of industry-standard network interfacing, SCSI support, and UNIX compatibility suggest that the TT may be an ideal platform for business, software development, and education, all markets that place a strong emphasis on low cost, connectivity, and standardization of resources. These, indeed, are what the TT offers in abundance.