Chapter 2 • Computer Systems 33Mainframe Computers
Mainframesare the heart of the computing systems for
many, perhaps most, major corporations and government
agencies. The early history of computing is the story of the
various generations of mainframe computers. The range of
mainframe power and cost is wide, with MFLOPS varying
from 2,500 to 1,000,000 and cost from $500,000 to
$20,000,000. The strength of mainframes is the versatility
of the applications they can handle: online and batch pro-
cessing, standard business applications, engineering and
scientific applications, network control, systems develop-
ment, Web serving, and more. Mainframes also operate as
very large servers in a client/server environment. Because
of the continuing importance of mainframes in corporate
computing, a wide variety of applications and systems
software has been developed for these machines.
Historically, competition was fierce in the main-
frame arena because of its central role in computing. The
dominant vendor has been IBM since the late 1950s. The
current generation of IBM mainframes is the System z
family (formerly the zSeries, and before that the
System/390). The newest models are the System z10
machines (see Figure 2.7), introduced in 2008, and they
vary from a single-processor model to a 64-processor
model. All these machines are built around the IBM multi-
chip module (MCM) and quad-core processor chips (four
processors on one chip). The System z10 is a symmetric
multiprocessor (SMP) machine, so each processor can be
handling a different application. The high-end (Enterprise
Class) machines are built using a modular multibook
design that supports one to four books per machine. Each
book contains an MCM, which hosts the processor chips
(up to five processor chips per book), storage control chips,
and high-speed interfaces for input/output.
The top-of-the-line, 64-processor System z10
Enterprise Class employs 4 such MCMs and can have up to
1,520 gigabytes (million bytes) of main memory. Even more
impressive, the System z10 Enterprise Class provides a 50 to
100 percent performance improvement over its predecessor.
IBM argues that the z10 is the equivalent of nearly 1,500
Intel- or AMD-based servers and that it can support
hundreds of millions of users. In addition to more speed and
capacity, the System z10 incorporates stronger security
features than other computers, higher availability, and
greater management control over the use of IT resources.
Furthermore, multiple systems can be combined in a
Parallel Sysplex, a multisystem environment that acts like a
single system. Through a combination of hardware and
software, especially the z/OS operating system, a System
z10 Parallel Sysplex can incorporate up to 32 individual
machines, each of which can have up to 64 processors
(Gonsalves, 2008; IBM Web site, 2010b). IBM has main-
tained its preeminent position in the mainframe arena
through solid technical products, excellent and extensive
software, extremely reliable machines, and unmatched serv-
ice (Hamm, 2009b).
Direct competition in the mainframe arena is less
fierce than it used to be. Two vendors, Amdahl and
Hitachi (Japan), dropped out of the mainframe market in- Amdahl was purchased by Fujitsu (Japan), and
Hitachi bowed out of the mainframe market to concen-
trate on other market segments. Amdahl and Hitachi are
particularly interesting cases because they succeeded for
many years by building machines that were virtually
identical to IBM’s, often with slightly newer technology,
and then by selling them for a lower price. The only
remaining major players in the mainframe market (in
addition to IBM) are Fujitsu and Unisys. Unisys was
formed years ago as the merger of Burroughs and Sperry
(Sperry built the very first production-line computer), so
Unisys has been in the mainframe business a long time.
However, there is plenty of indirect competition in the
mainframe arena, as vendors like Hewlett-Packard and
Sun Microsystems try to get customers to migrate their
mainframe systems to high-end servers.
FIGURE 2.7 IBM System z10 (Courtesy of IBM Corporation)