GUESS - The Network Is The Message

Author: Chet Heath, IBM Corporation, Boca Raton, Florida
Source: Personal Systems, 1991 Issue 2 (pages 23-30 physical)

This description of a concept called "workgroup computing" is reprinted from the recently published book The Micro Channel Architecture Handbook by Chet Heath and Winn L. Rosch. Information about the book follows the article (together with some other contextual snippets from the editor).

A Busmaster Example
About The Author
Editor's Note

A Busmaster Example

Not unlike the manner in which television allowed thought to be transmitted and converted rapidly into popular understanding as entertainment, a new medium has invaded the workplace - this time to efficiently allow us to coordinate our effort and direction when groups work toward common goals. Not insidiously, but silently, we absorbed the new philosophy by an evolutionary adaptation of our daily work habits. This "Trojan horse" of technology is the workgroup system. Its soldiers are made of software and silicon, and more than ever, they will free men to think rather than work.

When personal computers were first accepted in the workplace, they were perceived and promoted as individual tools (sometimes toys) of productivity. They followed "dumb" terminals that were dependent upon the vitality of distant resources, by providing the individual means required to accomplish routine desktop drudgery fully under the control, and sight, of the user. Beyond that, they did not imply large investment and could be justified by the improved productivity of the individual working alone. Simple individual tasks, such as composition of a letter, filing, or income tax preparation, justified the systems in the workplace and occasionally in the home. Perhaps most of all, the ability to reduce complex, numerically based decisions by way of the spreadsheet program cemented the PC into the workplace.

The isolated desktop could be made to exchange information within a group or office by physically exchanging the storage medium, the diskette. The inexpensive incorporation of the hard disk, with an initial capacity of 30 diskettes, led to local manipulation of information larger than the capacity of a single diskette. Further, the desire to control information located in the distant systems and to interact with that data led to a need to communicate in real time. The first connection was to the very same distant resources from which the desktop had earlier declared independence. But then, more slowly, it spread between the desktops, as workers became more dependent upon the output of their peers than on the distant resource.

The workers needed to network locally, much as medieval knights had in "round tables" centuries before them, or, as in more recent times, workers had convened around the water cooler. The success of the local area network, or LAN connectivity, between the electronic desktop systems is, therefore, a strong statement about the need of the modem knights of the desktop to band together to achieve common goals.

Figure 1. The GUESS Card

Why, if humans tend to herd together, are not personal systems initially designed as integrated workgroup systems rather than standalone boxes? It is because, like many inventions before it, the personal computer had to develop an individual following before it could be integrated into society. Airplanes preceded airports and airlines, electric lights glowed from batteries before power stations were established, and Bell spoke one-on-one with Watson long before the switchboard came along. Of course today air travel, electric light, and the telephone are integrated into vast standardized networks, and the design of the instrument at the user interface assumes that.

Until now, no personal system had been designed specifically to allow the desktops to collectively assemble into one force. The connectivity that allows users to congregate in a common network has so far been added as an "afterthought" peripheral attachment to stand-alone designs. The attachment was either through a bus-attached card, or similar logic on a system board, or outboard of the system entirely, through a peripheral port. It is now time for the personal system to integrate the interconnectivity of the network into its basic design. PS/2 systems with Micro Channel architecture have done exactly that.

When Micro Channel personal systems were first announced, it was stated that much of the new concept was very subtle in nature. One component, peer-to-peer bus master communication, was an element of that subtlety. Ironically, peer-to-peer implies interaction between individuals, like Bell and Watson, yet it is the building block of intercommunication.

Consider the following design concept, first publicly shown by IBM at the Computer Dealers Exposition (COMDEX) in Las Vegas, in the fall of 1989. It is not a product, but it could be, and it depends heavily on the foundation laid in place within PS/2 systems that implement standardized Micro Channel interfaces. It should not be inferred that IBM has any plans to market such a system; it is shown here merely as the author's example of the flexibility of Micro Channel architecture.

During the initial definition of the Micro Channel interface, the author had envisioned six conceptual tests of the extendability of the personal system. In one, the basic computer and its associated subsystem support components (such as interrupt controller, time-of-day clock, and system timer) would be assembled along with sufficient memory to contain an operating system and applications on a single card (Figure 1). Also resident on the card is the basic user interface of keyboard, mouse, VGA (or better) display, and compatible diagnostic ports, to make the "system on a card" serviceable.

The basic user interface is available from standard connectors on the rear bracket to the existing VGA, keyboard and pointing devices. It has been shown elsewhere that these interfaces can be propagated hundreds of feet.

As a bus master, this card could form the compatible heart of a system, requiring only the addition of disk, diskette, connectivity and printer interface on a system "Combo" board with power supply and cabinet for completion as in Figure 2.

Figure 2. A Small "Entry" System Based on a GUESS Card

This, in itself, is an exciting concept, but only begins the possibilities of such a design point. In a sense, the card is a system, less all the previously mentioned elements. To software, it forms a Generic User Environment of a Small System (GUESS).

Now plug a number of such GUESS cards into any PS/2 system with Micro Channel architecture to form a cluster of users in close proximity, as in Figure 3.

Figure 3. Cluster Host with Four GUESS cards

Because the cards are bus masters, and because the Micro Channel defines public memory on the bus or peripheral, each GUESS card can read from or write to memory located in the system or on other cards, even on other GUESS cards. The last property is called peer-to-peer bus master operation on the Micro Channel.

The concept could be made to work in a limited way for AT-based systems without peer-to-peer bus master communication. In such a system, a common system resource is assigned all data transfer responsibility, and the number of peripherally attached users becomes limited by the performance of that element. The central system resource is often the processor, and it already has enough to do. Dependence on a central resource is "designed-in" obsolescence, as the performance and number of users is limited by the collective load on the central resource, which is fixed in capacity at time of purchase.

The cluster host LAN does not have this defect. The GUESS card need only support its own data transfer requirements.As each GUESS card is added, the processor power to support its user is added to the system, and the connectivity to communicate is added as well. Micro Channel architecture and GUESS work together to maintain the user's asset in system unit and peripherals.

In theory, an operating system could be defined to coordinate access to common system elements, such as disk, printer, communication connectivity, and even bridge to external LAN. Such an operating system is a monumental task if taken as an isolated effort. Fortunately, there is an existing foundation to build on. Because Micro Channel multimaster arbitration uniquely grants the bus to one owner at a time, and because that owner is "publicly" declared on the arbitration bus, and again because of the public addressing of I/O, the Micro Channel interface can emulate a token ring LAN where the bus grant is the "token" and the bus address is the client or server address.

Further, peer-to-peer communication is a principal advantage of token ring over host connectivity because only one block transfer on the bus is required per message. Peer-to-peer communication and coordination of multiple processors and subsystems is the domain of a control block architecture, such as Micro Channel's Subsystem Control Block (SCB) architecture. Provision for resource allocation, error detection and recovery, and diagnostic isolation of the processors is the domain of Micro Channel Program Option Select (POS), Parity, and Channel Check protocols. Net: This concept "needs" PS/2's Micro Channel architecture.

The cluster host-attached peripherals, disk, diskette, LAN bridge, connectivity, and print adapters are then "served" to the GUESS card's attached users by modifications of standard local-area-network control programs. The cluster host "sees" each GUESS card as a user on a network, and each GUESS card "sees" the cluster host as the server. GUESS cards relate to each other as peer clients in the network. The resulting system is not diskless, because a portion of the system disk can be allocated to each user; however, the user interface is disketteless. The placement of the disk and diskette at a point physically removed from the user has security and environmental advantages and is actually desirable in many applications.

The utilization of the peripherals is no higher than that of a small LAN of eight users or less. The bus traffic may be reduced over a comparable LAN as the cards could use one transfer to communicate peer-to-peer with SCB-designated peripherals. A conventional server system would need at least two, and perhaps four, transfers with system memory and the microprocessor in order to move the same data. The network control program is helped by the SCB architecture by delegating part of its function out to the cards.

The Micro Channel interface has a default burst data transfer rate of 20 million bytes per second. As a local area network serial interface, that is equivalent to 160 megabits per second or 10 times present token ring network speeds. Net: Actual performance should exceed that of a comparable small LAN.

Consider the impact on the user and system owner of such a configuration. In a conventional LAN topology, as in Figure 4, the server and clients each have many duplicated functions. Many of these functions do not contribute to data movement or, like the diskette or client LAN card, have very low utilization in normal operation.

Figure 4. Conventional LAN Topology

In a cluster of GUESS cards, each user is supported by a card rather than a system unit. In effect, the card plugs into a server, as in Figure 5.

Figure 5. Cluster Host LAN Topology

Because all of the basic I/O functions are provided by the "cluster host" system, the user has the basic function of the desktop system less the cost of frames, covers, local disk and diskette, local area network card, and much of the system board logic required to build a conventional system. These elements can be a majority of the cost in a system. Net: The per-user cost of attachment should be less than a comparable conventional LAN design.

Furthermore, because the GUESS connected users share the system peripherals, the cost of those peripherals is "amortized" over all the users, and the cost of the system is thereby reduced additionally. Therefore, a centralized SCSI file system can outperform the lower-cost file systems of small desktop systems, yet the cost per user "seat" in the system is less than eight such small disk systems.

An optical "FDDI" LAN, as in Figure 6, may be prohibitively expensive if connected to each client in a conventional LAN topology. It would cost as little as one seventh as much per user if added as part of the cluster host system. A similar scenario exists for the incorporation of a centralized numeric processor, like IBM's i860-based Wizard card in the cluster host.

Figure 6. Fourteen-User System with FDDI LAN and Dual SCSI File Systems

The concept is flexible. It is believed that the GUESS card can emulate an "X-Window" with a real processor instead of a virtual one. The real processor stores applications in slower, less expensive RAM on the GUESS card, rather than the high-speed RAM of the central AIX system. In the configuration shown at COMDEX, a 7437 small, 370-based Micro Channel product ran VM (SP5). It provided PROFS mainframe host 3279-like attachment across the Micro Channel via a "virtual" 3274 control unit emulated in software, with virtual TCA and DCA cards as mailbox windows in the system RAM of a cluster host PS/2 Model 80. The interface to users was the familiar "hot key" between host VM applications and DOS on the GUESS card. No external dependency on a mainframe was required for basic operation (however, such connectivity was not designed out, either). Net: The per-user cost of entire systems may be further reduced over a conventional LAN or host attachment configurations.

The client's power supply, LAN attach card, LAN wiring, the multiplexing address units of conventional LANs, and the mechanical disk and diskette systems are major contributors to the failure rate of LAN-connected personal computers of any bus design. The elimination of these elements from the GUESS card improves the reliability of the user interface several fold. The availability of each server to the conventional network is dependent on the server's power supply and file system. The same is true for the cluster host design. An uninterruptible power supply will protect the server in a conventional LAN; with cluster host, it protects the clustered clients as well. Because the clients draw the power of a card rather than that of a system, up to 90 percent of the electric power per client can be conserved. It is therefore economical to provide such protection. Net: The reliability of a cluster host-based LAN can, in theory, exceed that of a conventional LAN topology.

In a conventional LAN, a client can be brought off-line for service without interrupting the availability of the system to other clients. One shortcoming of the cluster host LAN is that the entire cluster must be powered down to service a GUESS card, interrupting a system in continuous operation. Modern component reliability can reduce the probability of such an interruption of availability to a rare occurrence. This loss of availability during service operations is not a concern when service can be scheduled for idle periods. Inoperative stations can be cycled off-line by POS while awaiting service.

The potential exists for the GUESS card to assume the system's duties and control peripheral adapters and memory much as the system would, albeit at degraded performance levels, because the GUESS card is a master and a system on the bus as well. Such operation could conceivably be invoked manually or perhaps with very complex software automatically. Net: Availability can be made equivalent to conventional LANs in most scenarios.

Another consideration with the cluster host LAN is the cost of wiring. Where a facility has been wired for token ring, that wiring can be used to interconnect clusters rather than individual users in the conventional LAN. This provides up to an eight-to-one cost effectiveness for existing wiring with the cluster host LAN. Due to the limitation in cable length from the cluster host, if users are spaced at a distance greater than a few hundred feet from the cluster, it may be advantageous to bridge to token ring for that set of users. Where users are clustered in close proximity, like in many service industries, the cluster host LAN topology is advantageous. One hybrid configuration is achieved when a desktop system is shared between two adjacent workspaces, as in Figure 7.

Figure 7. Hybrid Two-User System

The system, with diskette and peripheral devices, is at the left hand of one user and the right hand of another. The same hybrid might appear as a two-user transportable system with a GUESS card installed in a P70 system.

Potentially, bridging to conventional LAN has other advantages. Only the transfers that "escape" the cluster appear on the LAN. Local departmental traffic need not occupy or burden the network. Only one token ring address may need to be consumed per cluster, potentially raising the total number of stations on the LAN to 1024, rather than the normal limit of 256. When systems initially load programs to the diskless stations on power-up, the cluster host LAN can transfer a full 16-megabyte system memory load theoretically in a fraction of the time of conventional token ring LAN.

The concept is highly dependent upon characteristics of the Micro Channel interface. Fully 85 percent of the system can be purchased today in the form of high-end PS/2 systems, with the advantages of the approach being derived from the dual use of the Micro Channel interface as an ultra-high-speed data transmission path, as well as the peripheral attachment means. Yet, much work lies between concept and reality with this new approach to workgroup systems. New LAN control programs, new hardware packaging, BIOS, diagnostics and Power On Self-Test procedures must be designed. New means of bridging to conventional LANs must be defined. It is even possible that an insurmountable obstacle may be discovered that prevents implementation of the concept altogether. Yet with IBM's open disclosure of the concept to the industry, there will be many who are attracted to the challenge.

Where the conventional LAN is still implemented with stand-alone system designs, the external connectivity adds to both the cost and failure rate of the system. The serial LAN data throughput acts as a limiter to performance of the distributed intelligence.

Alternately, the integration of the workgroup computer designs out the limitations of conventional LANs, and does for the group what the PC did for individuals: it gives them autonomy. The next logical step is the integrated workgroup computer, where "the network is the Micro Channel."

About The Author

Chet Heath is a Senior Member of Technical Staff at IBM's Entry Systems Laboratory in his 21st year with IBM. He holds B.S. and M.S. degrees in electrical engineering. Chet was lead engineer for the definition of Micro Channel architecture and gave the architecture its name. He has published many articles explaining architecture and workgroup computing in technical journals and the trade press. He has received IBM Quality and Author awards.

He has earned IBM's eighth-level invention award, Outstanding Technical Achievement, Outstanding Innovation, and Corporate Technical Achievement awards for his work on Micro Channel architecture and other inventions.

The Micro Channel Architecture Handbook was written to accommodate the needs of both beginning and advanced users. It is a guide to the Micro Channel, from the basic overview to a detailed look at every discrete function found in IBM PS/2 Model 50 through the new RISC System/6000 workstations, and beyond. It includes ideas and insights for system design applications. The introduction was written by Dr. Robert L. Carberry, IBM Vice President.

The Micro Channel Architecture Handbook, written and copyrighted by Chet Heath and Winn L. Rosch, is published by Brady Division of Simon & Schuster, Inc. The ISBN number is 0-13-583493-7.


GUESS (Generic User Environment of a Small System) was Chet Heath's idea for a cluster computer built from multiple peer-to-peer busmaster MCA adapters. Each card was essentially a single-board computer with its own CPU, memory, and user I/O.

IBM wasn't interested in making an actual product out of it. When Chet left IBM in 2000 he took the idea with him (with IBM's blessing) and founded OmniCluster - read HERE.

The product they shipped was for the PCI bus, but the idea remained the same...

Editor's Note

I was forced off the internet for three weeks, and only had the MCAH, MCA-Revolution, Model 80 Tech Ref (-041/-071) and a few sections from the '90 HITR. The moment of revelation is Chet Heath referring to MCA as an Expansion Bus, one where individual busmasters could operate, communicating with each other and the system CPU if they needed to.

The significant part was if they needed to. There is nothing in MCA saying the "associate processor" has to use any specific system resource.

I see now that the AOX MicroMaster 486 with the video port was edging towards this. It was never to be since AOX sold the MicroMaster to Kingston.

Today's System on a Chip (SoC) have CPU, ethernet, video, HD/memory controller, and USB integrated into a chip. Why not a Single Board Computer (SBC) to fit a 32-bit MCA slot? Imagine a Win7 compatible MCA SBC. All the cries of disbelief... Think of the ROMP Crossbow. The 68K YARC. The i860 Wizard. The whatever P/390... Just a few of the MAD ideas in my head. -LFO

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