- - Decision Resources, Inc. Bay Colony Corporate Center Information Systems Industry 1100 Winter Street Waltham, Massachusetts 02154 Telephone 617.487.3700 Future Computing Environments: Telefax 617.487.5750 The Commodity Mainframe Era Gordon Bell Consultant to Decision Resources, Inc. The success of large-scale, multimilliondollar main- frames built from ECL technology and running pre Business Implications prietary operating systems from IBM and other The structure of mainframes renders them un- hardware vendors (e.g., Fujitsu, Hitachi, NEC, and competitive against micrebased multiprocessor Unisys) has clearly peaked. While some analysts fore- computers. These micro-based systems also cast the overall mainframe market to increase at 24% have cost advantages in manufacturing, software (less than half that of personal computers and work- volumes, interactivity, and a base of trained us- stations), others forecast a shrinking market for main- ers and programmers. frames. We believe that the mainframe hardware market will be eaten away by alternative technologies, The industry is transitioning from servercentric but large-scale transaction-oriented applications will and clientcentric environments to client-server, client-multipleserver, and network computing grow moderately. with multiple clients and multiple servers. This Mainframes operate as a central facility for batch transition will take another decade because mis- processing, large transaction processing workloads, sion-critical legacy applications cannot readily and general-purpose computing. Mainframes require be migrated to other environments. a large, specialized staff to maintain both hardware Resizing will continue to draw applications off and software. Created in the 1950s as the central mainframes onto networked PCs, workstations, computer for large enterprises, the mainframe now and small servers; simple multiprocessors; large is following the same fateful path as proprietary mini- scalable multiprocessors; and massively parallel computers, which, ironically, were created in the processing multicomputers. This trend will ac- 1970s for departmental applications and thrived on celerate as network cost, performance, and replacing mainframe functions. Minicomputer maintainability improve. growth is even more anemic than that of mainframes Simple multiprocessors will be the mainline of because the minicomputer failed to attract enough computing throughout this decade, to be re- missioncritical applications, which slow the migration placed eventually by various forms of highly to PCs and workstations. parallel processing computers. This environ- With the advent of open systems 1 based on Unix, ment will be based on standards, making com- DOS, and industry standards, proprietary systems ponents more commodity-like and the market (particularly mainframes and traditional minicom- more competitive. If this future environment is based on a few communications and com- puting standards, the market for computers will 1. The IEEE defines an open system as "a comprehensive and con- become vastly larger than it is today. sistent set of international information technology standards and functional standards profiles that specify interfaces, services, and supporting formats to accomplish interoperability and port- ability of applications, data, and people." Press Date: December 20,1993 puters) are out of favor. Unix became widely used in ported and to which additional computers can be U.S. universities beginning in the early 1910s, result- added incrementally. ing in a significant base of trained Unix programmers and users. Similarly, the wide-scale adoption of PCs Why Today's IBM Mainframes Are has established the largest base of computer users. Obsolete The mainframe has no such loyal following, except, perhaps, in MIS departments. Even mainframe pro- To make the assertion that, like the dinosaur, the grammers are dwindling as older programmers retire water-cooled ECL-technology mainframe is obsolete, and new trainees gravitate toward Unix and DOS we must first dissect it to examine the arcane struc- environments. ture required to support its software. Figure 1 shows the structure of the largest mainframe based on the Beginning a little over 10 years ago, workstations be- IBM 360 architecture, the IBM ES 9000, which dictates came a natural choice for users hampered by over- the structure of IBM-compatible mainframes such as loaded minicomputers and mainframes. Enabled the Arndahl5000 Series. by fast, inexpensive, CMOS microprocessors, a bit- mapped graphic workstation provided high interac- The mainframe's performance relies on two inde- tivity. Soon workstations and workstation servers pendent (but tightly connected) parts sharing a connected to a local area network (LAN) replaced single operating system and clusters that have shared minicomputers for departmental and interactive input/output (I/O) . The ES 9000 has two quasi- computing. In the late 1980s, a LAN-based PC envi- independent subsystems, each having shared mem- ronment based on Novel1 NetWare servers came into ory, up to four central processors (that may be added prominence, connecting Microsoft DOS and incrementally), and a switch to interconnect the parts. Windows-based PCs. While this structure is essential for fault-tolerance, it may not meet the performance requirements for very Today there are a multitude of computing alterna- large applications. Clustering technology is required tives to the original IBM 360 architecture-the basis to scale beyond a single computer with eight proces- for the majority of mainframes installed. (Mainframes sors. The complexity of processor/memory intercon- from NEC and Unisys have architectures similar to nections limits mainframes to eight processors per the IBM 360.) Most of these mainframe alternatives computer; clustering is limited as well. For all practi- fall into one of the following categories: cal purposes, about six mainframes can be clustered Multipocasor. A computer architecture in which when they also have multiple processors. two or more processors share common memory. The combination of multiprocessing and clustering (Most mainframes and supercomputers are also creates additional complexity that increases the soft- multiprocessors.) ware burden of every large application. The IBM Multi. A microprocessor-based multiprocessor that 360's complex operating system and arcane architec- typically supports fewer than 20 processors, where ture are maintained by an ever-dwindling base of the microprocessors are organized around a single programmers who tend to resist new computing archi- bus. tectures. In this predictable scenario, the fewer the mainframe programmers, the less likely companies Computer Cluster. A collection of independent com- will commit to new mainframe purchases; and the puters (i.e., each computer runs its own copy of the fewer the mainframes purchased, the less likely new operating system) that are interconnected to sup port a single application. The maximum number programmers will be trained on its architecture. of computers supported is typically fewer than 16. The duplexed mainframe comprises pairs of comput- (Most mainframes can be clustered.) ers and software programs. The following describes some of their specialized control functions. Scalable Multi. A multi that has no theoretical limit on the number of microprocessors supported and The 1/0 control portion of the main computer to which additional microprocessors can be added operating system (including MVS, VM, AIX) exe- incrementally. cutes channel commands. This structure is not suited to Unix, which is inherently small-file- and Scalable Cluster. A computer cluster that has no character I/O-based. theoretical limit on the number of computers sup- SPECTRUM Information Systems Industry Future Computing Environments Decision Resources, Inc. Press Date: December 20, 1993 Figure 1 Duplexed IBM Mainframe Structure Console computer (connected to all processors/ controllers) Source: Gordon Bell. The Storage Management Subsystem (SMS) con- memory. (Some data transmission delays can be offset trols disks and archival storage. In addition to the by increasing throughput.) main control computer, controllers and disks in- Multis, however, have a simple 1/0 structure whereby clude computers not visible to users. a disk (with a track buffer) reads directly into main The access interface (VTAM) allows the operating memory under the control of an ordinary processor. system to access the 3274 or 3745 communications Disk caches are located in main memory and can be computers and their operating systems. traded off with other memory demands. Because all resources are available and interchangeable, any The console computer monitors the main computer processor or memory can be used for application, and corrects errors. control of communication, disk, and caching at any Computers within 1/0 devices and controllers that level. Compared with duplexed mainframe disks, are not visible to users. redundant arrays of independent (or inexpensive) disks (RAID) reduces overhead and can increase per- Computers and operating systems increase software formance by up to a factor of 4. size and complexity, automatically increase total mem- ory, and cause data transmission delays. For example, Whereas the relatively high cost of mainframes limits disk caching and buffering occur within the disk, disk the number that are built, multis sell in an order-of- controller, storage computer, 1/0 channels, and main magnitude-higher