{'fraction_non_alphanumeric': 0.041478653245400905, 'fraction_numerical': 0.016140229087122527, 'mean_word_length': 4.421448730009407, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Hard Disk Drive as a Magnetomechanical Logic Device

We consider the conditions how two binary numbers can be superimposed on the same track with the use of different recording magnetic fields. As a result the average magnetization of longitudinal medium along the track can have three states: -M, 0 and +M. Possibility to perform logic operations with these states is considered. We demonstrate OR, AND, XOR and NOT operations and discuss a modification of a recording device.


I. INTRODUCTION
ARD DISK drive is usually used as just a storage device in personal computers. Here we consider a possibility to perform logic operations on a hard disk drive. This can be done on a magnetic recording medium in which there is a possibility to superimpose binary information. Such media consist of magnetic particles with i) different anisotropy fields and/or with ii) different anisotropy axes orientations. The first is, for example, an oriented (e.g., perpendicular) medium with a distribution of anisotropy fields. The second is typical for a longitudinal medium where the anisotropy axes of particles are distributed randomly.
The elementary logic operation consists of three steps: 1) Applying a strong magnetic field, one writes the first binary number A as the transitions between different average magnetization states (-M and +M, all previous information is erased). 2) Using smaller magnetic field that reverses just a part of magnetic particles, we write the second binary number B. Doing so we obtain transitions between 0 and M, -M and 0, and -M and M. 3) The reading sensor detects the peaks of magnetization variation between the uniformly magnetized regions on the recording magnetic surface and gives result of the logic operation OR, AND, XOR or NOT. Using the results of XOR and AND operations, we can construct an adder.

II. SUPERIMPOSITION OF THE BINARY INFORMATION
Let us demonstrate how the binary information can be superimposed on the recording track. We shall consider a longitudinal medium containing identical particles with the uni-axial anisotropy field K H and randomly distributed anisotropy axes in the disk plane. If the external magnetic field The resulting magnetization is a sum of magnetizations of "type 1" and "type 2" particles. It is equal to zero if 2 3 / 2 0.87 The binary information is written on the type 2 particles in this case (see, Fig. 2b

III. LOGIC OPERATIONS
In order to develop logic operations, we need to represent the binary numbers in a doubled form changing 0 by 00 and 1 by 11. For example, the binary number 11010 should be represented in the following form (11)(11)(00)(11)(00). Here the parentheses are shown for simplicity of representation. Technically this representation can be made with the doubling of the clock frequency.

B. XOR operation
We can introduce a concept of a "negative" (-I) pulse. In this case the pulse is considered down relative to M or M/2 states. In Fig. 3b we see an example how the binary number B=I00I is shown in a negative form -B=-I00-I. In other words, -B is a reversed magnetization profile of B relative to horizontal axis M=0. It is easy to check that (B)OR(-B)=0000. Figure 3 illustrates the XOR operation. Superimposing the first number A = I0I0 and the second number B (in the form of -B = -I00-I), we obtain the resulting magnetization profile C = 00I-I. So far as the sign of the pulse in C does not matter for a peak detector, C = 00II = (I0I0)XOR(I00I) = (A)XOR(B).
Actually, XOR logic operation can also be obtained from Fig. 2c if one assumes that a peak detector can separate signals with 2M and M variations. As it was mentioned above, for 2M variation (left peak in Fig. 2c) we have AND operation (all other signals are zeros). For M variation (two smaller peaks in the right side of Fig. 2c) we have XOR operation (with the assumption that for 2M variation signal is zero for this specific peak detector).

C. NOT operation
Consider the following operation: (0)OR(-I) = -I. We can neglect the sign (a peak detector detects just the magnetization variation) and write (0)OR(-I) =I. In addition, as it was pointed out above, we have (I)OR(-I)=0. Thus, OR operation with -I inverts the initial binary number, and NOT operation is just OR operation for any binary number and corresponding sequence of -I.

E. Block diagram
A block diagram of the logic device is similar to hard disk drive conventional block diagram (see, e.g., [1]) with some modifications.
The input sequentially gives binary numbers and the instruction to perform logic operations OR, XOR, AND or NOT. For example, A=1010 and B=1001.
Modulation creates the voltage signal corresponding to A (and then B) for the recording head.
Recording system consists of recording head, recording medium and reading sensor. Changing the current of the recording head, we apply the magnetic fields 1 H ± and 2 H ± to the recording medium. The reading sensor detects the magnetization transitions.
The peak detector reads the signal of the reading sensor and detects the peaks of magnetization variation. A simple peak detector does not distinguish the small variations (the transitions between -M/2 and M/2, -M and 0, or 0 and M) and large variations (the transitions between -M and M). An advanced peak detector can detect the only large transitions (between -M and M) and makes it possible to perform AND operation (see, Fig. 2c).
Finally, a decoder transforms I=11 to 1 and 0=00 to 0 and sends it to output.

IV. DISCUSSION
All the above description regarding the superimposed binary information and logic operations is applicable also for an oriented (perpendicular) recording media. For example, one can use the perpendicular medium with two types of particles with the uniaxial anisotropy fields