Storage Addressing; Storage Sharing; Storage Protection; Absolute Addresses - Control Data 3100 Reference Manual

STORAGE ADDRESSING
Table 2-1 gives the absolute addresses for a specific storage capacity.
TABLE 2-1. ABSOLUTE ADDRESSES
Storage
Word Encompassing Addresses
Capacity
4K
00000
~ 07777
(4.096)
8K ALL PRECEDING ADDRESSES AND:
(8.192) 10000 ~17777
16K ALL PRECEDING ADDRESSES AND:
(16.384) 20000 ; 37777
32K ALL PRECEDING ADDRESSES AND:
(32.76~)
40000
~
77777
NOTE
If an address is referenced that exceeds the storage capacity of a system, the uppermost
digit is adjusted to conform to the available storage. No fault indication is given for this case.
Example: Address 67344 referenced.
Actual address referenced: 67344 -32 K system
27344-16K system
07344- 8K system
07344- 4K system
STORAGE SHARING
Two 3100 Computers may share the memory of a 3109 Storage Module. A switch on
each Storage Module Control Panel allows the operator to give exclusive control to the
right or left computer. A middle position on this switch actuates a two-position priority
scanner. Storage Control honors the requests in the order they are received. Neither
computer has priority over the other, and the computer involved in the current storage
cycle relinquishes control to the requesting computer at the end of its cycle. Either
computer can therefore be delayed a maximum of one storage cycle. A similar program
delay may occur within either computer when an internal scanner determines whether
Main Control or Block Control has access to the storage module.
Direct access to 3100 type storage modules is available for certain Installations. The
normal I/O channel route is bypassed and the customer's special equipment interfaces
directly with the storage logic.
STORAGE PROTECTION
It is often desirable to protect the contents of certain storage addresses against altera-
tion during the execution of a program. There are three catagories of addresses: those
that are always protected; those that are protected at the option of the programmer;
and those that are never protected during special sequences.
An attempt to write at a protected address is defined as an Illegal Write. No writing
actually takes place, however, and the attempt to write does not stop or interrupt the
execution of the program. An Illegal Write causes a console indicator to light and the
program may sense an Illegal Write as bit 05 of the internal status response code. An
Illegal Write is cleared by a Master Clear, an Internal Clear, or by sensing.
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Rev. 8