24 IBM ^ zSeries 990 Technical Guide
2.1 System structure
The z990 structure and design are the result of the continuous evolution of S/390 and zSeries
since CMOS servers were introduced in 1994. The structure and design have been
continuously improved, adding more capacity, performance, functionality, and connectivity.
The objective of z990 system structure and design is to offer a flexible infrastructure to
accommodate a wide range of operating systems and applications, whether they be
traditional or emerging e-business applications based on WebSphere, Java, and Linux, for
integration and deployment in heterogeneous business solutions.
For that purpose, the z990 introduces a superscalar microprocessor architecture, improving
uniprocessor performance, and providing an increase in the number of usable processors per
system. In order to keep a balanced system, the I/O bandwidth and available memory sizes
have been increased accordingly.
2.1.1 Book concept
The z990 Central Processor Complex (CPC) introduces a packaging concept based on
books. A book contains processors (PUs), memory, and connectors to I/O cages and ICB-4
links. Books are located in the CEC cage in Frame A. A z990 server (CPC) has at least one
book, but may have up to four books installed.
A book and its components is shown in Figure 2-1. Each book contains:
򐂰 12 Processor Units (PUs). The PUs reside on microprocessor chips located on a
Multi-Chip Module (MCM).
򐂰 16 GB to 64 GB physical memory. There are always two memory cards, each containing
8, 16, or 32 GB.
򐂰 Three Memory Bus Adapters (MBAs), supporting up to 12 Self-Timed Interconnects
(STIs) to the I/O cages and/or ICB-4 channels.
Figure 2-1 Book structure and components
Up to four books can reside in the CEC cage. Books plug into cards, which plug into slots of
the CEC cage board.
STI Slots
MCM
Memory cards
Chapter 2. System structure and design 25
Power
Each book get its power from two Distributed Converter Assemblies (DCA) that reside on the
opposite side of the CEC board. The DCAs provide the required power for the book. Each
book is supported by two DCAs. The N+1 power supply design means that there is more DCA
capacity than is required for the book. If one DCA fails, the power requirement for a book can
still be satisfied from the remaining DCA. The DCAs can be concurrently maintained, which
means that replacement of one DCA can be done without taking the book down.
Between two sets of DCAs you find the location of the oscillator cards (OSC) and the optional
external time reference cards (ETR). If installed, there are two ETR ports to which an optional
Sysplex Timer® can be connected. Seen from the top, the packaging of a four-book system
appears as shown (schematically) in Figure 2-2.
Figure 2-2 Book and power packaging (top view)
Located within each book is a card on which the Memory Bus Adapters (MBAs) are located.
The card has three MBAs, each driving four STIs (see Figure 2-8 on page 32).
Figure 2-2 also illustrates the order of book installation:
򐂰 In a one-book model, only book 0 is present.
򐂰 A two-book model has books 0 and 1.
򐂰 A three-book model has books 0, 1, and 2.
򐂰 A four-book model has books 0, 1, 2, and 3.
Book installation to up to four books can be concurrent.
Cooling
The z990 is an air-cooled system assisted by refrigeration. Refrigeration is provided by a
closed-loop liquid cooling subsystem. The entire cooling subsystem has a modular
construction. Its components and functions are found throughout the cages, and are made up
of three subsystems:
1. The Modular Refrigeration Units (MRU)
One or two MRUs (MRU0 and MRU1), located in the front of the A-cage above the
books, provide refrigeration to the content of the books together with Motor Drive
Assemblies in (MDAs) in the rear.
A one-book system has MRU0 installed. Upgrading to a two-book system causes
MRU1 to be installed, providing all refrigeration needs for a four-book system.
Concurrent repair of an MRU is possible by taking advantage of the hybrid cooling
implementation described in the next section.
DCA00
DCA01
DCA11
DCA10
DCA21
DCA20
DCA31
DCA30
DCA01
2xOSC 00/01 2xETR 00/01
Book3
Book0
Book1
Book2
Memory Cards
Memory Cards
Memory Cards
Memory Cards
MCM
MCM
MCM
MCM

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