This document summarizes a patent for an apparatus that stores digital data on a moving magnetic medium. It allows for simultaneously reading stored data from a cell on the medium and overriding it by writing new data to the same cell. This is accomplished by using timing impulses to select cells for reading and writing, with the reading gate occurring slightly before the writing gate. This allows time to determine if the cell contents need to be changed based on the read data and other inputs, before overriding the data during the writing gate. The document describes the technical details and diagrams of how this works.

1. * GB780030 (A)
Description: GB780030 (A) ? 1957-07-31
Apparatus for storing digital data on a moving magnetic medium
Description of GB780030 (A)
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The EPO does not accept any responsibility for the accuracy of data
and information originating from other authorities than the EPO; in
particular, the EPO does not guarantee that they are complete,
up-to-date or fit for specific purposes.
PATENT SPECiIFCATION
Date of Application and filing Complete
Specification: Dec. 15, 1953.
709030 No. 34940/53.
Application made in Netherlands on Dec. 29, 1952.
Complete Specification Published: July 31, 1957.
Index at aceptance:- geiss 106(), 0 1I A I nternaftnnaD
CRassaficaun:-GO8", The inventor of this invention in the sense of
being the actual deviser thereof within the meaning of Section 16 of
the Patents Act, 1949, is Leendert Kosten, a subject of the Queen of
the Netherlands, of 16, Duchattelstraat, The Hague, the Netherlands.
COMPLETE SPECIFICATION
Apparatus for Storing Digital Data on a Moving Magnetic Medium We,
STAATSBEDRIJF DER POSTERIJEN, TELEGRAFIE EN TELEFONIE, a Public
Department of the Netherlands, of Kortenaerkade 12, The Hague, the
Netherlands, do hereby declare the invention, for which we pray that a

2. patent may be granted to us, and the method by which it is to be
performed, to be particularly described in and by the following
statement: For recording large quantities of coded information, use is
often made of a movable magnetic wire, tape, disk or drum as the
information storage medium. The information is often recorded in a
binary form in fixed spots on this medium (the information cells) by
means of differences in magnetization.
For the purpose of electromagnetic writing on and reading from the
medium, the position of a given information cell is determined 20by
the selection of a specified recorder or reproducer, or by time
selection.
When information has once been recorded on the medium, it is preserved
for an arbitrarily long time. Other types of recording systems
(mercury tube memory, electrostatic memory) do not possess this
quality.
In said other types of recording system the information stored in each
cell must be read within a rather short time to be re80written. Thus
each element of information is constantly refreshed.
It is possible at any refreshing moment in these systems to read the
old information contained in a cell and to record at the same time new
information in its place. This possibility is inherent of the
regenerative character of the recording system.
In an ordinary non-regenerative magnetic recording system it is
possible to change at suitable moments the information contained in
specified cells. Because of the large writing signal, however, it is
not possible, in that case, to read the old information at the same
time. The invention provides means for reading the information
contained in a cell [Price 3/6] and overriding it by writing other
information in its place simultaneously (or practically
simultaneously) at the same selection moment.
The invention will be described in connection with the example
(illustrated in Fig.
1 of the accompanying drawings) of a magnetic drum, on which only one
magnetic head will be used for writing upon, and for reading from the
drum, and consequently, involv- s5 ing only one track on the drum. The
drum has a second track on which a series of equidistant impulses has
been stored. The signal extracted from this track, when passed through
the amplifier KV and the impulse 60 regenerator IR results in a series
of impulses (the timing impulses), which mark on the information track
a number of spots equal to the number of impulses of the timing
impulse track. The neighbourhoods of these 65 spots are the
information cells. Gating impulses pi, and pi, for the selection of
cells with a view to writing into and reading from these cells,
respectively, are derived from the timing impulses ki. 70 It is

3. supposed, though this is not essential, that the magnetic medium is
originally neutral and that the binary digits " 1 " and "0" are
written into a given cell by the transmission of short current
impulses of different directions through the magnetic head.
Fig. 2 shows at a and d the curves of these impulses plotted against
time, in this figure the time scale must be taken in relation to the
equidistant timing impulses mentioned 80 above. If in the cell under
review a " 1 " has been recorded and if this " 1 " is overridden in a
next revolution at the correct instant by a " 0," the medium will
assume practically the same condition as if a " 0" had been 85 written
directly. Thus the after-effect of former recordings is negligible.
If in a revolution in which no writing occurs, the voltages appearing
at the terminals of the magnetic head are plotted 90 -- - A 'S.-S
780,030 against time, the curve obtained will have a character as
shown in Fig. 2 at c or f according as the last digit recorded has
been a " 1" or a "0." By sufficient amplification and by the use of
the gate operating in the hatched interval a definite determination of
the last recorded digit can be obtained. The reading pulse operates on
the reading gate during the interval represented by the right-hand
hatched period and the writing pulse during the interval represented
by the left-hand hatched period.
Curves b and e show the magnetisation of the drum after its passage
under a head excited with either a 1 (curve a) or a 0 (curve d). This
magnetisation corresponds with that (curves a or d) of the head and
takes into account the diffusion effect due to the finite size of the
head and the finite air-gap between the head and drum. During a
succeeding drum revolution, the voltages induced in the head, as
represented by curves c and f, are obtained by differentiation from
curves b and e, with a similar diffusion.
If the air-gap or slot of the magnetic head were infinitely narrow and
the clearance between the head and the medium were infinitely small,
the recording of one element would cause the magnetization of an area
called herein area A equal to air-gap width in the direction of travel
times the distance covered tangentially by the drum in an interval
equal to the recording gate impulse.
As the said air-gap-width and distance are 35not infinitely small,
there will be a certain diffusion of the magnetic field. As a result
of this the actually magnetized area per cell will be larger than the
said defined area A.
Further, during the reading operation a magnetic dipole lying on the
medium will already have an appreciable influence on the magnetic head
before this dipole has arrived right under the air-gap. The diffusion
effects occurring during writing and reading add up, so that in the
case of reading, a notable signal can be obtained at a moment (in

4. relation to the timing impulse) lying before the interval in which the
writing impulse for recording occurs (see Fig. 2).
Consequently, it is possible to place the reading gate impulses a
short time before the recording gate impulses. In carrying out the
present invention, this effect is made use of for scanning during a
revolution the information from a cell during a reading gate impulse
and changing. if necessary, the content of this cell during the
immediately following writing gate impulse. The time between the
reading and writing gate impulses is available for determining, if
necessary from the information read together with information supplied
from another source, any new information to be stored in the cell.
Fig. 3 gives the diagram of such an instal651ation. The timing
impulses picked up by the magnetic head KI, are amplified by KV and
regenerated by IR. These impulses are directly applied, as impulses
pi2, to the reading gate P2, through which the signals coming from the
information head K, as amplifled by AV can pass.
The signal passed by P.) at a certain moment arrives at a device RO,
which may be a computing device and in which it is determined from the
information carried by this 75 signal and from other information
present in RO or supplied from the outside, whether, and in the
affirmative case. which new information must be recorded in the
relevant cell.
The term " computing " in computing device is used in this case in the
broad sense of forming new coded information by the application of
logical operations on given information. This information may be
passed from RO to Ki as a writing signal, a 85 suitable part of this
signal being passed by gate P. The gate impulse pi. applied to P, is
obtained from the timing impulse ki, suitably delayed by the impulse
delay circuit IV.
The circuit described exhibits another difficulty, in that during the
recording of new information a large current impulse is sent through
Ki; this current impulse causes also a large voltage impulse at the
input of AV.
This voltage impulse may be as much as 80 95 db above the level of the
reading signal normally to be handled by AV.
If, as is normal, AV is an a.c. amplifier, it becomes so overloaded
during the writing operation that it is for some time irresponsive to
reading. The time during which this irresponsiveness exits is long
relatively to the periods of the lowest frequency components of the
reading signal.
As the amplifier AV must be able to 105 handle the information
recorded in the next cell, a serious limitation as regards the number
of cells per unit length in a tangential direction is imposed on the
system.

5. In order to avoid this difficulty AV may 110 be arranged as a d.c.
amplifier, the anode and screen grid voltages being obtained from
batteries or from electronically stabilized voltage sources (so having
no inertia). In that case over-control does not entail
irresponsiveness. This solution. however, is not very attractive.
According to this invention a data processing arrangement comprising a
processing device for deriving bv means of logical operations new
coded information from given information, a device for recording coded
information on a movable ferromagnetic medium by means of a magnetic
head and for reading as determined by a reading gate 125 recorded
information from this medium by means of the same head. recording into
and reading from the information cells on this medium being effected
by time selection, the information read being fed to the said device
13 780,030 and the information to be recorded originating from this
device, in which arrangement during one passage of the medium each
time selection impulse for reading from a cell arrives at the reading
gate a little earlier than that for recording information in the same
cell and in which arrangement, moreover, the said device determines
from the information extracted under control of a given reading
selecting impulse and from any information available in another way,
whether, and, in the affirmative case, which information shall be
substituted for the extracted information in the said cell during the
recording selecting impulse immediately following the said given
reading selecting impulse, is characterized in that the signals read
by the magnetic head are modulated on a carrier current having a
frequency which is large with respect to the frequency of reading
successive information cells and in that the modulated signals are
subsequently amplified and detector and then led to the gate
controlling the reading operation.
In practising the present invention instead of the direct current
amplifier AV, use is made of a combination of a carrier oscillator 0,
a modulator M, a high frequency amplifier V and a detector D. An
embodiment of the invention is illustrated in Fig. 4 of the
accompanying drawings.
In Fig. 4, 0 is a carrier oscillator, the frequency of which is large
with respect to the highest frequency essentially present in the
reading signal from Ki. M is a ring modulator to which the carrier
current is applied and in which it is modulated with the signal from
Ki. The modulated carrier is then amplified in V. D is a detector in
which the signal is detected. The detected signal is applied to P2
(see Fig. 3). In order to obtain different states of P2 for 1 or 0 as
read, M must be adjusted to be " out of balance."
For this purpose use can be made of the variable resistor Rd shown, or
of a polarizing voltage inserted in the cross connection.

6. The gate P, of Fig. 3 is represented in Fig.
4 by the double triode. As a result of the connection, by means of
rectifiers, between the grids of this tube and the conductors coming
from RO and point pi, which are all normally at a potential of e.g.,
-20 V, neither triode normally carries any current.
The series connection of the cathode resistors R7, and R1.0 produces
an attenuation of only a few dB during the reading operation.
If a " 1" has to be recorded, potential of e.g., + 10 V is applied by
left-hand conductor RO. As soon as the gate impulse appears, the grid
potential of the left-hand triode rises to +10 V and anode current
begins to flow. The cathode current flows partially through resistor
R,1, partially through the series connection KX and R7u,.
The resistors are so dimensioned that the latter current flowing
through Ki and R7, is large enough for writing a " 1 " on the drum.
The recording of a " 0 " is done in an analogous way by means of the
right-hand triode.
In this case the current flow through Ki is 70 in the Opposite
direction.
During the writing operation a large voltage is applied to Ki and also
reaches V, which is rendered irresponsive in consequence. This is due
to changes in energy 75 content of various reactive coupling and
decoupling elements also under the influence of detection phenomena
attendant upon the large voltage aforesaid. Actually V needs only to
amplify frequencies in the neighbourhood of the carrier frequency.
Consequently, the relaxation times of coupling and decoupling circuits
need only to be a little larger than the carrier period. Decay times
of circuits may be chosen somewhat larger. The 85 abnormal state of V
passes to the normal one practically in a time of the order of a few
times the said intervals, that is in a few carrier periods. As this
period is small with respect to the high frequency practically 90
occurring in the reading signal, and consequently, still more with
respect to the interval between two timing impulses, the amplifier V
can have reached, after a recording impulse, its normal state again
before the 95 arrival of the next reading gate impulse.
The detector D can work at such a high energy level that overcontrol
during writing can be avoided by simple means, such as limiting
rectifiers. 100
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