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1.2.1.1 Central Processing Unit (CPU)
The central processing unit (CPU) controls the execution of all instructions
and processes. The CPU circuits contain the logic, arithmetic, and control
functions used by the system. DECsystem 5500 systems use the RISC-
based KN220 CPU module set.
1.2.1.2 Console Serial Line Unit (SLU)
Each system has a serial line unit connecting the console terminal to the
system. The SLU connector (a modified modular jack) is located on the CPU
cover panel. The console serial line provides a means of communicating
with the CPU.
1.2.1.3 Main Memory
Main memory provides the electrical storage area for data and instructions
used by the CPU. When you start your system, the operating system is
loaded into main memory. Application programs must also be loaded into
memory.
When the system cannot load everything into memory at once, it reads
in units of data called pages (512 bytes of data) from disk. A large main
memory increases the efficiency of processing, since fewer pages must be
copied to and from the disk. Each configuration comes with a standard
memory option and capacity for up to four memory modules. By adding
more main memory, you can increase efficiency.
The contents of memory are volatile.
This means they are lost when
you turn off power to the system. Use mass storage devices, such as
integrated storage elements and tape cartridges, to store software and data
permanently.
1.2.1.4 Network Controller
Network communications controllers allow you to connect to an Ethernet
network. With a network connection and appropriate network software, you
can use network services, such as mail; access data stored on other systems;
perform operations, such as editing and printing on remote systems; and
share resources, such as laser printers.
Your system comes with an
on-board Ethernet controller that is part of the CPU module set. The
system can be connected to either a standard Ethernet cable or a ThinWire
Ethernet cable. Connectors for both types of cables are on the CPU cover
panel.
System Overview
1–19
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