An example of a four-wire core with all windings is
shown in figure 6-9.
. Drive lines —Each drive line provides 1/2 of the
current necessary to change the state of the core. In
other words, current must flow in the same direction in
both drive lines to change the direction of magnetic flux
in the core (zero to one or one to zero).
. Sense line —The sense line is used when reading
data from cores. The sense line detects the change in
state of the core from one to zero.
. Inhibit line —The inhibit line is used during the
write or restoring process. Current flow in the inhibit
line opposes or inhibits the drive line currents
attempting to change a core from zero to one. Simply
put, the inhibit line inhibits writing ones.
THREE-WIRE CORES.— A three-wire core
uses a digit line, a word line, and a sense line. The
digit and word lines combine to perform the functions
of the X and Y drive lines and the inhibit line. The sense
line performs the same function as in the four-wire
cores.
CORE STORAGE LAYOUT.— As each core can
store but one binary bit of data, large numbers of cores
are required for effective storage of large amounts of
data. Core storage or core memory is designed to store
a fixed number of memory words. Each core stores
Figure 6-9.—Four-wire magnetic core.
one bit position of one of the memory words. The
length of a memory word (number of bit positions)
varies from system to system, but common lengths
include 8, 16,32, and 64 bits. The size of core storage,
or its memory capacity, is determined by the number
of memory words that can be used or addressed to store
and retrieve data.
To accommodate the memory
capacity of any size, the memory words are organized
into matrices.
Matrices.— Magnetic cores are arranged into
matrices to simplify addressing, reading, and writing
operations. An example of a basic four-wire magnetic
core matrix is shown in figure 6-10. Each core in the
matrix must have 2 drive lines (X and Y), an inhibit line,
and a sense line intersecting through the center of the
core. The most common four-wire core matrix is the
64 by 64 array. We base our discussion of matrices on
this size.
Arrays — A 64 by 64 array contains 64 X drive
lines and 64 Y drive lines. By selecting one X drive line
and one Y drive line, read and write current can be
applied to any one of the 4096 (64 × 64 = 4096) cores
in the array. As each drive line contains 1/2 of the read
or write current, only the core with full read or write
current passing through it will be switched. The inhibit
line is threaded in parallel with the X or Y drive lines.
Figure 6-10.—Four-wire magnetic core matrix.
6-10
