Power, Cooling – IBM 990 User Manual

Page 37

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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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