Specifications

Escala Tower PL & S, E, T System Hardware
Chapter 1: Family Overview 13/30
9es3s1c1.doc
Rev 5.9
02/12/2003
The approach adopted utilizes a memory bus to carry only simple address tags and to use a non-
blocking crossbar switch for data traffic. This crossbar switch is used to interconnect up to 4 dual-CPU
ports, an I/O port and the memory sub-system.
Following the setup phase of a transaction, e.g. posting an address on the address bus, the data can then
be transferred at full clock speed through the switch. This is possible through a private point to point
link created for each separate transaction. Therefore there is no further contention. It is also possible to
perform several operations in parallel, such as multiple accesses to memory or cache to cache transfers.
The fact that PowerScale addresses both high speed memory interfacing and cache to cache transfers
makes it suitable for managing faster processors and larger caches in the future.
This has enabled Bull to build a range of systems around a single architecture, with the in-built
flexibility to upgrade both horizontally, by adding processors, or vertically, by upgrading through the
generations of PowerPC.
The Escala models have the following major attributes:
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The operating system can schedule and synchronize work across the available processors.
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A high-bandwidth bus is provided for access between cache and memory.
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Cache and memory are efficiently managed to provide cache consistency.
An example of how the design of the Escala servers can maximize performance follows:
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The most recently used or projected to use program elements are kept in L1 cache (fastest access).
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Programs and control objects are kept in L2 cache (next fastest).
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Directories to databases are kept in memory (next fastest to L2 cache).
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Actual databases are stored on disk drives.
Reliability and availability are key concerns for any commercial system. In a widely distributed
environment, this becomes more critical. To address this, the Bull design provides remote as well as
local control.
The Escala servers include features, such as embedded support processors, that enable remote
operation of the system; remote power-on and power-off; running of diagnostics, service, repair and
console support, and processor reconfiguration in case of errors. The support processor is continuously
powered even when system power is off.
The mirrored console support means that remote service actions are visible and controlled by the
customer. This includes control over whether the system can be restarted or not.
An additional feature is that the system can be set to dial a remote service or support point should the
system fail, and a surveillance function allows the system to detect "hang" conditions in the system and
if necessary invoke a rapid restart.
In addition to the support processor, the error checking and correction circuitry protecting memory is
able to detect and correct all single-bit failures. Double-bit errors are also detected and auto-restart
invoked.