The internal Memory System for PDP-3 consists of modules of 4096 words
of coincident current magnetic core storage. Each word has 36 bits. The
memory modules operate with a read-rewrite cycle time of 5 microseconds.
The driving currents of the memory are automatically adjusted to
compensate for normal room temperature variations.
Each core memory module consists of the memory stack, the required X and
Y switches, the X and Y current sources and sense amplifiers for that
stack.
The Memory Address Register, the Memory Buffer Register, and the Memory
Timing Controls are considered to be part of the Central Processor. The
standard PDP-3 Memory Address Register configuration is built to allow
up to 8 modules of core memory (32,768 words). There is a space in the
addressing section of the machine to allow expansion of the addressing
by a factor of eight for a total addressing capacity of 262,144 memory
registers.
The Core Memory may be supplemented by Magnetic Tape Storage. This is
described under Input-Output.