Computing Fabrics (1998-2003)

On May 19, 2003: Eric Lundquist, Editor-in-Chief of eWeek, recognized that IBM's On-Demand Computing, HP's Adaptive Enterprise, and Sun's N1 are all movements towards Computing Fabrics as we first predicted them in 1998.

On January 7, 2002: eWeek called our 1998 Computing Fabrics Cover Story "Prescient"
and declared The Grid, a subset of Computing Fabrics, "The Next Big Thing".

Riding the
Third Wave

In the News 2002-2004

Computing's Next Wave 1998
(The First Report)

The Next Big Thing 2002
Computing Fabrics & Grids

The Three Waves of Computing


Defined & Compared


Conferences & Workshops

The Bigger Picture


Computing's Next Wave
Computing Fabrics Stories - 1998

Full Text of Selected Infomaniacs' Guides, Analyses, and Reviews
Technologies of Computing Fabrics
By Erick Von Schweber and Linda Von Schweber
PC Week Online
November 1, 1998 4:43 PM ET

+ Computing Fabrics technical description
+ Distributed shared-memory architectures
+ Modularly scalable interconnects
+ Distributed operating systems
+ Hypernetworks

Related Stories
Computing's Next Wave
(in print and on-line)
This is the main story.
Distributed UNIX Soon May Be Woven into the NT Fabric
(in print and on-line)
Computing Fabrics to Refashion Industry
(on-line only)
The Technologies of Computing Fabrics
(on-line only)

A Computing Fabric consists of nodes--packages of processors, memory and peripherals--that are linked together by an interconnect. Within the Fabric are regions of nodes and interconnections that are so tightly coupled they appear to be a single node. These are cells.

Tight coupling within a cell is achieved with hardware, software or both, although the performance of the resulting cell varies significantly with the coupling implementation.

Cells in the Fabric are then loosely coupled with each other--a loose coupling of cells does not appear the same as a single node. The Fabric as a whole--or each cell within--can grow or shrink in a modular fashion, meaning nodes and links can be added and removed. Nodes from the Fabric surrounding a cell may join that cell, and nodes within a cell may leave that cell and join the surrounding Fabric. Cells can divide as well as fuse.

These characteristics can be summed up by saying that the boundaries of a Fabric, and the cells within, are potentially fluid.

Sophisticated software and hardware will be required to support the cellular characteristics of Computing Fabrics. Initially, the combination of a distributed operating system running on a distributed shared-memory architecture implemented using a modularly scalable interconnect will produce the desired results.

In time, as these technologies and a fourth, transparent, automated object distribution make their descent into the commodity space, clusters and networks will take on these cellular characteristics and become Computing Fabrics.

Distributed shared-memory architectures

Each cell of a Computing Fabric must present the image of a single system, even though it can consist of many nodes, because this greatly eases programming and system management. SSI (Single System Image) is the reason that symmetric multiprocessors have become so popular among the many parallel processing architectures.

However, all processors in an SMP (symmetric multiprocessing) system, whether a two-way Pentium Pro desktop or a 64-processor Sun Ultra Enterprise 10000 server, share and have uniform access to centralized system memory and secondary storage, with costs rising rapidly as additional processors are added, each requiring symmetric access.

The largest SMPs have no more than 64 processors because of this, although that number could double within the next two years. By dropping the requirement of uniform access, CC-NUMA (Cache Coherent--Non-Uniform Memory Access) systems, such as the SGI/Cray Origin 2000, can distribute memory throughout a system rather than centralize memory as SMPs do, and they can still provide each processor with access to all the memory in the system, although now nonuniformly.

CC-NUMA is a type of distributed shared memory. Nonuniform access means that, theoretically, memory local to a processor can be addressed far faster than the memory of a remote processor. Reality, however, is not so clear-cut. An SGI Origin's worst-case latency of 800 nanoseconds is significantly better (shorter) than the several-thousand-nanosecond latency of most SMP systems. The net result is greater scalability for CC-NUMA, with current implementations, such as the Origin, reaching 128 processors. That number is expected to climb to 1,024 processors within two years. And CC-NUMA retains the single system image and single address space of an SMP system, easing programming and management.

Although clusters are beginning to offer a single point for system management, they don't support a true single system image and a single address space, as do CC-NUMA and SMP designs. Bottom line: CC-NUMA, as a distributed shared-memory architecture, enables an easily programmed single system image across multiple processors and is compatible with a modularly scalable interconnect, making it an ideal architecture for Computing Fabrics.

Modularly scalable interconnects

A Computing Fabric must support modular growth (and shrinkage). Most multiprocessors lack modularity: A system that's expected to grow to 32 or 64 processors must be ordered equipped to handle its maximum of 32 or 64 processors, even if it's delivered with only eight to begin with.

The culprit is the system bus or crossbar switch that most multiprocessors use to interconnect processors, memory and peripherals. The bus or switch must be sufficiently big and fast to support the maximum number of processors regardless of how few processors the system has when ordered.

In contrast, an SGI Origin can start out with eight processors and grow to 128 without requiring the upfront purchase of the entire infrastructure. The Origin accomplishes this with a modular interconnect, called Craylink, that can be expanded in the field as processors are added to the system. In other words, the Fabric grows with the system, made possible by a proprietary SGI application-specific integrated circuit called the Spider chip, with system cost scaling linearly with system size.

The modularity of the Fabric also means it doesn't present a single point of failure, as do the buses and centralized crossbar switches, and the modified hypercube connectivity automatically routes around failed or saturated links. A current 128-processor Origin 2000 provides 20.5G bps of bandwidth between processors on opposite sides of the system, called bisection bandwidth.

Modular interconnects are not an invention of SGI, however. They've been integral to massively parallel systems for well over a decade--found, for example, in the nCube2, Thinking Machines Corp.'s Connection Machine, the Alpha-based Avalon A12 and others. The news is SGI's forthcoming implementation of rich modular interconnects in Intel space, coupled with CC-NUMA.

Distributed operating systems

The cellular boundaries of a Computing Fabric must be easily reconfigurable. In SGI's Origin 2000, power domains--units of processors, memory and switching components that share a power supply--form a minimal cell and run a copy of Cellular Irix. One or more cells can be taken out of service, repaired or replaced, then returned to service--all while others remain operational.

Assemblies of power domains can similarly be treated as a cell. SGI's Cellular Irix enables massively distributed operation while improving availability and serviceability, giving Unix a dramatic edge over Windows NT.


Cells within Computing Fabrics will also need to be loosely coupled while maintaining high performance. Gigabyte system networks, the next generation of SANs (system area networks), will layer the Scheduled Transfer protocol atop HIPPI-6400 and its successors for VIA (Virtual Interface Architecture) compatibility.

HIPPI-6400 switches will accept network interface cards for Gigabit Ethernet, fiber channel and other protocols, supporting bandwidth aggregation (e.g., 900-port gigabit Ethernet switches). These next-generation SANs may ultimately merge with modularly scalable interconnects to form hypernetworks.

Transparent automated object distribution: Tight coupling, necessary to form cells in a Computing Fabric, can also be achieved in software, where the operating system handles distribution of objects, rather than memory pages, across coupled machines. This frees programmers from low-level details, allowing them to work at a high level of abstraction while optimizing performance under varying conditions.

The Millennium project at Microsoft Research supports transparent distribution of COM (Component Object Model) and COM+ objects. To speed performance across a SAN that is tightly coupled in this fashion, DCOM (Distributed COM) is being layered atop VIA, providing a huge reduction in the time it takes for objects and method invocations to travel between nodes.

Interoperability is critical to this vision if Computing Fabrics are to be fully exploited. Either a standard modular interconnect must be adopted by all--a dubious prospect--or a standardized interface between nonstandard interconnects must be available, which is a more likely scenario.

An example of this is the Scheduled Transfer protocol for supporting heterogeneous VIA clusters, now in the standardization process.

Seamless connectivity is only half the equation. Although support for heterogeneous Fabrics is primarily a political problem, creating heterogeneous cells is a technical issue, likely to require significant R&D. Two or more Fabrics running different distributed operating systems could loosely couple as a cluster, but it would be superior if a variety of distributed operating systems could tightly couple to form a cell, collaborating in support of a single system image and a single object space.

Microsoft's Millennium has the potential to accomplish this with software. Funding such efforts should not be a problem if Computing Fabrics take off, as we anticipate they will.

Erick Von Schweber and Linda Von Schweber are principals of Infomaniacs, a think tank, specializing in technology convergence. They can be reached at or

Copyright © 1998 Ziff-Davis Publishing Company

By Linda Von Schweber
& Erick Von Schweber

Copyright 1996-2004 by Infomaniacs. All Rights Reserved.
Updated May 28, 2003