Magnetic Cores - IBM 709 General Information Manual

BINARY OCTAL DECIMAL
0 0 0
1 1 1
10
2 2
11
3 3
100
4 4
101
5
5
110
6 6
III 7 7
At this point a carry to the next higher position of
the number is necessary, since all eight symbols in the
octal system have been used.
1000
1001
1010
1011
10
II
12
13
8
9
10
11
As far as the internal circuitry of the computer is con-
cerned, it only understands binary ones and zeros.
The octal system is used to provide a shorthand
method of reading and writing binary numbers so
that the contents of a register, when shown on the
operator's panel, may be read directly. This is shown
in Figure 4, using a 36-digit binary number.
Reg; ster contents (b; nary)
Octal value
Figure 4. Binary Representation of Register Contents
Magnetic Cores
The main storage medium for many computers is the
magnetic core.
Each magnetic core is a ring or doughnut shaped
piece of ferromagnetic material. The cores "remem-
ber" information indefinitely, and can recall it in a
few millionths of a second. When a wire is inserted
through the hollow center of a core (Figure 5), an
electrical current passed along the wire sets up a mag-
netic field around the wire. This field magnetizes the
core. When the current is removed, the core remains
magnetized. 1£ a current is passed along the wire in
Core Is Set
Figure 5. Magnetic Core Action
the opposite direction, the magnetic field set up
around the wire is reversed. When this occurs, the
core is said to have "flipped" or changed its mag-
netic state. A "sense" wire is inserted through the
core and, when the core flips, a small electrical voltage
is sent along the sense wire. This voltage may then
be amplified and used in the computer (Figure 6).
Computer
Figure 6. Flipping of a Magnetic Core
As with the magnetic core, all computer elements
are able to represent two states. These two distinct
states provide the basis by which these elements hold
information. For this reason, the elements are called
bi-stable elements. For example, one state may be
interpreted as the digit 0; the other, as 1. Similarly,
the elements may be used to represent: plus or minus,
on or off, yes or no, and so on. Several of these ele-
ments are shown in Figure 7.
The
IBM
709 and 7090 Data Processing Systems use
high-speed core storage units. Each unit is divided
into distinct sections called locations. Each location
is uniquely identified by a number assigned to it. This
identifying number is called an address because just
as a street address denotes the precise location of a
particular building on that street, this number de-
liD .. State
Figure 7. Bi·stable Computer Elements
Introduction 7