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Plug-in units are powered by the system, but in addition bus PIUs have
their own power regulators. Batteries supply power to the system cabinet
for approximately 11 minutes. Expander cabinets have their own supply.
Plug-in units (PIUs)
Self-contained assemblies that are easily installed in the system cabinet or
expander cabinet. There are PIUs for the XMI bus, the VAXBI bus, disks,
and batteries.
Reset sequence
A process leading to the execution of a copy of the console firmware from
memory. Purpose is to test the machine, establish the console environ-
ment, indicate that the console is executing, and dispatch to entry han-
dling procedures. Power-up testing executes from the backup cache, a boot
processor is determined, which creates the HWRPB and copies the console
image from ROM/cache to memory. Registers are set to their default val-
ues, and internal console data structures are initialized. After power-up
the secondary processors also use the console code from memory.
SCSI (Small Computer System Interface)
An industry-standard interface for connecting disks and other peripheral
devices to computer systems. Requires the KZMSA XMI adapter.
SCSI PIU
Houses SCSI based disks and tapes inside system and expander cabinets
(BA655).
SROM (serial ROM) code
The initialization code that bootstraps the main console/diagnostic firm-
ware.
Symmetric multiprocessing
A multiprocessing system configuration in which all processors have equal
access to operating system code residing in shared memory and can per-
form all, or almost all, system tasks.
Transactions
LSB transactions consist of a command and four data cycles, which follow
some fixed time after an arbitration cycle. All LSB modules monitor the re-
quest lines to see which of them wins the bus. Up to three transactions can
be in progress at one time. Because arbitration occurs on a dedicated set of
control lines, it can overlap with data transfer.
Glossary-8
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