WO1987000959A1

WO1987000959A1 - Data storage apparatus for digital data processing system

Info

Publication number: WO1987000959A1
Application number: PCT/US1986/001631
Authority: WO
Inventors: David Cope; Gary Spletter
Original assignee: David Cope; Gary Spletter
Priority date: 1985-08-08
Filing date: 1986-08-06
Publication date: 1987-02-12
Also published as: CA1278861C; JPS63500904A; EP0233254A4; EP0233254A1

Abstract

A data storage device (10) for use in a digital data processing system that stores digital data in addressable storage locations on a stationary planar magnetic medium (14). The storage device includes a magnetic head module (13) that, in turn, includes a plurality of individually energizable read/write heads (20) forming an array across one surface of the module, the individual heads corresponding to the addresses. The magnetic medium is placed in juxtaposition with the surface of the module that includes the array. When a head is energized it generates a magnetic field to magnaetize a region of the magnetic medium proximate the head thereby to store data on the medium. To read data from the medium, the head is energized to generate a magnetic field in a selected direction. An electrical voltage is generated in the head winding, the amplitude of which indicates the value of the stored data. After the location is read, the data is re-written in the location.

Description

_DATA STORAGE APPARATUS FOR DIGITAL DATA PROCESSING SYSTEM

Background of the Invention

1. Field of the Invention

The invention relates generally to the field of digital data processing systems, and more specifically to data storage apparatus for use in such systems. The invention provides a low cost, high speed and high capacity data storage system that uses removable magnetic media on which to store data.

2. Description of the Prior Art A digital data processing system generally includes three basic elements; namely a memory element, an input/output element, and a processor element, all interconnected by one or more buses. The memory element stores data in addressable storage locations. This data includes both operands and instructions for processing the operands. The processor element causes data to be transferred, or fetched, to it from the memory element, interprets the incoming data as either instructions or operands, and processes the operands in accordance with the instructions. The results are then stored in addressed locations in the memory element. An input/output element also communicates with the memory element in order to transfer data into the system and to obtain the processed data from it. The units comprising the input/output element normally operate in accordance with control information supplied to it by the processor element. The units comprising the input/output element may include, for example, printers, teletypewriters, or keyboards and video display terminals, and may also include secondary data storage devices such as disk drives or tape drives.

The data storage devices that are used in a digital data processing system and its disk and tape drives essentially forms a hierarchy based on cost per unit storage (typically a bit), access speed, that is, the speed that data can be written (stored) in or read (fetched) from the device, and capacity, with the electronic storage used in main memory typically being relatively high speed and high cost but low capacity, and the magnetic storage used in disk and tape drives being relatively higher capacity but. lower speed and lower cost. In addition, a processor itself may also include a private electronic storage such as a cache. memory, which has higher access speed to the processor than does the main memory, with higher cost per storage element, but with typically far lower capacity than the main memory.

In recent years, significant efforts have been made to improve the access speed and the capacity of the magnetic storage units and also reduce the costs. Using disk drives as an example, data is stored on one or mo.re rotating disks whose surfaces are coated with a magnetic . material. A radially-movable read/write head suspended above the disk surface reads data from and writes data onto the magnetic coating on the disk surface. The head is maintained a uniform distance from the disk surface by the air that is entrained with the rotating disk; essentially the head "flies" over the disk surface. Efforts at increasing disk capacity have required the heads to fly closer and closer to the disk surface. This results in problems, however, as the head is susceptible to "crashing" into the disk surface in the event of power interruptions or mechanical vibration. In addition, irregularities in the disk surface and also dust particles on the surface that are attracted by the magnetic fields representing the stored data can create problems with uniform flying. In some low-performance disk drives, such as is characteristic of floppy disks, the heads rest on the disk surface. This alleviates problems of head crashing, but since the head contacts the moving disk surface, the head and recording medium tend to abrade each other.

In modern disk drives, the read/write head moves radially with respect to the disk, and so data is stored on the disk in concentric rings, or tracks, each representing one radial position of the head. The tracks are divided into a plurality of equi-angular sectors, with each sector storing a selected amount of data. typically five hundred and twelve eight-bit bytes or a multiple thereof. When the disk drive is requested to access, that is, read data from or write data onto a specific sector or sectors, the drive must first perform a search operation, that is, move the head to the appropriate track and then a seek operation, or wait for the disk to rotate until the sector is under the head, before data can be transferred. The search and seek operations can take a significant amount of time, on the order of at least ten milliseconds in current high- performance drives to several hundred milliseconds for floppy disk drives. In even the fastest drives the search and seek operations take significantly longer than the actual time required to perform the data transfer. In an effort to reduce the search and seek times, some manufacturers have added additional heads around the periphery of the disk. However, this adds to the cost of the drive and does not appreciably reduce the search and seek times or increase data transfer rates. " Since the access time for the disk drives is so long, high performance processors could execute thousands of instructions during this time, and so modern operating systems are configured to permit interrupting a program which requires a disk access and begin processing another program which has sufficient data already in main memory to facilitate execution. These context switches. however, require processing overhead to store the current program's context and call in a new one, during which time no useful operations are being performed on user programs. In addition, some operating systems provide scheduling arrangements in which a number of disk transfers may be queued and initiated as the head steps across the various tracks in each direction, that is, as the head steps toward the center moving in one direction and toward the rim moving in the other direction, rather than in the order in which they are generated, which may result in transfers that are randomly distributed across the disk. This tends to reduce the access time, but the scheduling programs also comprise overhead on the processor that reduces the computing that the processor could be performing on user applications.

Furthermore, as with most electromechanical portions of digital data processing systems, the disk's rotational mechanism and the head movement mechanism are the parts that are most highly prone to failure. This tends to limit or reduce the reliability of the entire system, as the disk and tape drives are required for high capacity storage in modern systems.

As has been noted, the electronic main random access memory alleviates many of these problems, but it is significantly more expensive, on a cost per bit basis,- than is magnetic storage. Furthermore, electronic storage is volatile, that is, the stored charge dissipates when the power is turned off, and the memory, unlike magnetic storage, does not have a removable medium. Thus, unlike the magnetic storage, the random access memory cannot be used for loading programs or data into the computer system.

Summary of the Invention

The invention provides a new and improved data storage device for use in a digital data processing system that uses a magnetic medium for storing the data which, as in some disk and tape storage devices, may be removable, but which eliminates many -deficiencies in current magnetic storage devices, including head crashing or head and media wear, electromechanical failures and the lengthy search and seek times that are required to access data in other storage devices which use magnetic storage media.

In brief, the invention provides a new and improved data storage device in which data is stored in a planar magnetic medium. A plurality of small, individually energizable read/write heads, one head per bit of data, are supported and maintained in a matrix arrangement adjacent to the magnetic medium. Circuitry is provided to individually enable each head to read data from or write data onto the medium. To write data onto the medium, circuitry energizes the head to impress a magnetic field onto the medium in a selected direction, with the impressed field in one direction representing a binary "1", and a field in the opposite direction representing a binary "0". To read data that has previously been written, circuitry enables the head to generate magnetic flux in a selected direction. If the field that had previously been impressed on the medium is in the opposite direction as the field then generated by the head, a relatively large electrical pulse is generated which is sensed by the circuitry which energizes the head; If the previously-impressed field was in the same direction as the field generated by the head, a reduced electrical pu-lse is generated, which also is sensed. The amplitude of the pulse indicates the value of the stored data, which is transmitted to other units in the system. Since the previously-written data is destroyed by the reading operation , the circuitry energizes the heads to re-write the data. The medium and heads do not move in the new data storage device and since each read/write head is continuously adjacent to its data stored on the medium, no time is required to move the head to the data, and so the search and seek times are zero. Eliminating head movement also eliminates the possibility of head crashing and wear of the head and medium. In addition, eliminating moving parts enhances reliability of the data storage device and of the entire computer system.

The data storage device, including the read/write heads may be manufactured using thin film techniques that are used in the semiconductor industry. That is, the heads may be formed in layers to form the U-shaped heads and the energizing windings which surround them, as well as the conducting wires that connect them to the energizing and sense circuitry. The invention also provides a new circuit for selectively energizing the individual heads.

In an alternate embodiment, the medium may be formed directly over the lead matrix of the data storage device using a thin film technique. The medium may cover the entire surface in juxtaposition with the heads, or alternatively, it may be patterned so as to provide magnetic material only across the head gaps. Brief Description of the Drawings The invention will be pointed out with particularity in the appended claims. The above and other advantages of the invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: Fig. 1 is an exploded perspective view of a data storage device constructed in accordance with this invention;

Fig. 2 is a diagram, in perspective view, of a detail of a magnetic head module comprising a portion of the storage device depicted in Fig. 1;

Fig. 3, comprising Figs. 3A and 3B, are side and top schematic sectional views, respectively of a single read/write head used in the magnetic head module depicted in Fig. 2;

Fig. 4 is a schematic diagram of energizing and switching circuitry used with the storage device depicted in Fig. 1; and

Fig. 5, comprising Figs. 5 and 5B, depict alternative embodiments of read/write heads useful in the data storage device depicted in Fig. 1.

Detailed Description of an Illustative Embodiment

With reference to Fig. 1, a magnetic storage device 10 constructed in accordance with the invention includes a substrate supporting, body 11 which supports a plurality of switching chips 12 on its upper surface and electrically connects to chips 12 through pins on the underside of the chips (not shown) that mate with a socket 16. The substrate 11 also supports a plurality of magnetic head modules 13 on its lower surface that connect through pins 17 to the substrate 11 through sockets (not shown). The magnetic head modules which" are described in more detail in connection with Figs. 3, 3A and 3B, contain the actual read/write heads, are maintained in close contact with a planar recording medium 14 by a sp ing-loaded , retractable plate 18. The recording medium 14 has magnetic coating 15 on its upper surface which contacts the magnetic head modules and provides the actual magnetic recording medium for storing data. The switching chips 12 contain circuitry which will be described below in connection with Fig. 4 which selects the individual ones of the read/write- heads which will be described in connection with Fig. 2.

In brief, a digital data processing system (not shown) , when it desires to obtain data from a mass storage device such as a disk drive or data storage device 10, transmits a data transfer command identifying a read or write operation and an address over a bus (also not shown) which is received and decoded by control circuitry external to device 10. The address identifies, for a disk drive, a block of data by its track and sector number and, for storage device 10, a block of data by its magnetic head module and a group of read/write heads. The external circuitry operates in a conventional manner to energize switching modules 12. The switching modules couple signals through substrate 11, which includes conductors which couple signals from switching chips 12 through pins 17 to magnetic head modules 13 and allow the heads identified by the address from the system to be energized in a selected manner to permit data to be written onto, or read from, medium 14. The data is represented by magnetic flux in the magnetic coating in a selected direction adjacent to the read/write head.

With reference to Fig. 2, a magnetic head module 13 includes a plurality of U-shaped heads 20 that are arrayed in a regular matrix pattern in a non-conductive and non-magnetic binder 19, with the open -ends of the U- shaped heads facing towards the lower surface 21 of the head module. Encircling a portion of each ^'head is an individuallyenergizable electrically conductive winding 22. The conductor forming its associated winding is spaced slightly apart from its associated head to prevent it from being electrically shorted to the head, which may be conductive. When current passes through a winding, a magnetic field is induced in the head, with the direction of the field depending upon the direction of current flow through the winding.

Figs. 3A and 3B depict in schematic form side and top sectional views of one of the magnetic heads 20 and its respective winding 22 in magnetic head module. Although not illustrated in Figure 2, the magnetic head module also includes a plurality of -energizing wires including an input line 30 and an ou.tput line 31 which are connected to respective ends of winding 22. As will be shown below in connection with Fig. 4, windings associated with several heads may be connected to a single set of input and output lines 30 and 31. As is depicted in Fig. 3A and 3B, in one embodiment the magnetic head comprises an elongated cross member 40 of a magnetizable material that is formed parallel to the lower surface 42 of the magnetic head module against which magnetic medium 14 is maintained by plate 18. From the cross member 40, two legs 41 extend toward the lower surface 42. ^•

In the embodiment depicted in Figs. 3A and 3B, the winding 22 surrounds cross member 40. Thus, when switching modules 12-enable current to flow from input line 30 to output line 31, a magnetic field is induced in head 20 in the direction depicted by the arrows in the figure. In addition, a magnetic field is induced through the magnetic coating 15 on medium 14. When the current is removed, the magnetization that was impressed on medium 14 remains. ^■ The direction of magnetization is interpreted as a binary value and may be read by the switching chip transmitting a current in a selected direction through winding 22. If the magnetization previously impressed in the coating is in the opposite direction, the magnetization changes direction when the current pulse is transmitted, and, as it does, a relatively large voltage pulse occurs between input line 30 and output line 31. Alternatively, if the previously- impressed magnetization is in the same direction, only a 5 relatively small voltage pulse is generated. The pulse that is generated is sensed by circuitry in the switching chips. The voltage of the generated pulse indicates the value of the stored data. The switching chip then performs a writing operation to restore the magnetization

10 to its condition prior to the reading operation.

In one embodiment, the magnetic head modules 13 are formed using conventional thin film techniques that are similar to techniques used in fabricating integrated circuit chips. For example, the head module depicted in

15. Figs. 3A and 3B can be fabricated in a number of steps if lines 30 and 31 are formed at different vertical levels in the module, or in several fewer steps if they are formed at the same level. In the first step, if the fabrication begins at the lower surface 41, the portion

20 of the module including the binder 19 and the lower portion of legs 41 are formed from the lower surface 42 of module 13 up to the level of the lower surface 44 of winding 22. In the second step, the lower horizontal" portion of winding 22 from surface 44 up to surface 45,

25 as well as the corresponding level of legs 41 and binder 19. In the third step the portion of module 13 is fabricated from the surface 45 of winding 22 up to the lower surface- 46 of horizontal member 40, including portions of legs 41, binder 19, and the lower section of vertical portions 47 of winding 22. In the fourth step of the fabrication procedure, the portion of the module from the lower surface 46 to the upper surface 48 of cross member 40 are formed, including the horizontal member 40 and the mid-section of the vertical portions 47 of winding 22. In the fifth step the portion of the magnetic head module 13 from the upper surface 48 of cross member 40 to the lower surface 50 of winding 22, is fabricated, including the upper section of the vertical portion 47 of winding 22 and the associated binder 19. In the sixth step the portion of head module 13 is fabricated from the lower surface 50 to the upper surface 51 of the winding, including the upper horizontal portion of the winding and a vertical portion at the two ends of the winding which are to be connected to input and output leads 30 and 31. In the seventh step the portion of the magnetic head module 13 is fabricated from the upper surface 51 of the winding 22 to the lower surface 52 of output line 31, including the vertical portion connecting winding 22 to the input and output lines 30 and 31. In the subsequent steps portions of the magnetic head module are fabricated to the top surface 53 of wire 31, the bottom surface 54 of wire 30, and the upper surface 55 of wire 30 and portion of the module above the upper surface 55.

In all of the fabrication steps, thin film technology using conventional techniques of selective material deposition and removal, using masking operations that are well known in the art of integrated circuit fabrication technology, can be used to fabricate the magnetic head module 13.

Fig. 4 depicts a schematic diagram of circuitry that can be used to selectively energize the windings 22 in the- magnetic head modules. The input and output ends of windings 22 are connected through input and output lines 30 and 31 to input and output control switches 60 and 61. The input terminals of windings 22 are also connected through a plurality of load resistors 62 to a set of control lines 63 which are, in turn, connected through control switches 64 to a current source and sense circuitry generally represented by reference numeral 65. Circuitry 65 supplies current in one direction that is required to perform the appropriate writing or reading operation, and also senses the presence or absence of a pulse during a reading operation. In addition, circuitry 65 enables the data to be re-written after a reading operation. In addition, a second circuit 65A supplies current in the opposite direction through switches 64A, resistors 62A and control lines 63A. The operation of the circuit depicted in Fig. 4 is similar as between the operation using circuit 65 and the operation using circuit 65A, and so the operation will be described in connection with the use of circuit 65. As depicted in Fig. 4, the windings 22 and associated circuitry are divided into five groups, identified as groups A through E. Each of the windings 22 in a group is connected to the same input line 30 and to different output lines 31. The load resistors 62 and 62A that are connected to the different windings in each group are connected to different ones of the control lines 63 and 63A such that one winding from each of the ' groups A through E is connected through load resistors 62 and 62A, to each of the control lines 63 and 63A. In operation, to energize one of the windings 22 using circuit 65, the switching module 12 that decodes the address from the data processing system and identifies the winding associated to the addressed storage location, closes one of the switches 64 and one of the switches 61. The switching module 12 is enabled to close all of the switches 60 except for the switch corresponding to the closed one of switch 61. Thus, all of switches 60 are closed except for one, and only one of switches 64 and one of switches 61 are closed. This effectively isolates from the current source and sense circuitry all of the windings 22 except the one associated with the head corresponding to the addressed location.

As an example, if the winding to be energized is winding 22', the address decoding circuitry closes switch 64' and 61* and leaves open all of the rest of the switches in output switches 61 and control switches 64. ^• The address decoding circuitry also closes all of the switches 60 except for switch 60'. This ensures that current is not permitted to be coupled throug.h any of the other ones of windings 22 that may also be connected to the control line 63 that is connected to switch 64', since other current paths can exist through multiple windings from that control line to the output line 31 controlled by switch 61'. Thus, closing all of the switches 60 except for switch 60' ensures that only winding 22' receives any of the current from circuit 65. In addition, all of switches 64A are open to ensure that circuit 65A does not provide current to any of the windings. If circuit 65A is to be used to provide current to windings 22 in the opposite direction, switches 64A are used in the same manner as switches 64 described above, and the operation of switches 60 and 61 are interchanged. Thus, to energize one winding using circuit 65A, one of switches 64A is closed, one of switches 60 is closed, all but one of switches 61 are closed, and all of switches 64 are open.

Figs. 5A and 5B depict alternative embodiments of heads 20. Rather than being spaced apart, the heads can be essentially formed from a single cross member with adjacent heads sharing depending legs 41. In the embodiment depicted in Fig. 5A, the windings 22 are wound around the cross member 40, whereas in the embodiment depicted in Fig. 5B, the windings 22 are wound around the legs 41. To energize one head in the embodiment depicted in Fig. 5B, the switching modules must energize windings on adjacent ones of the legs 41 in opposite directions so that, for example,, the flux in one leg is up, the flux in the adjacent leg must be downward to complete a magnetic circuit through medium 14.

It will be appreciated that an alternate embodiment of the invention may provide a second set of head modules 13 opposing the modules depicted in Fig. 1, and in place of plate 18. In this embodiment, a suitable double-sided medium may be used, that is,-a medium comprising a planar carrier the sides of which carry the magnetic material. In use, the medium would be placed between the opposing head modules.

In addition, if the head modules are formed by thin film techniques as described above in connection with

Figs. 3A and 3B, if the medium need not be removable, it - may be deposited over lower surface 42. After being deposited, the medium may be patterned so as to provide magnetic material only between the legs 41.

It will also be appreciated that the invention provides a new data storage device that stores data on a removable magnetic medium but which reduces or eliminates many of the problems inherent in current magnetic storage devices which use moving magnetic medium. The invention makes possible much higher data densities than are possible with current disks, for example, as in disks only a limited annulus on the disk is available for storage and then only on widely-separated tracks, whereas data can be stored over»the entire medium surface in the invention. In addition, the medium used with the invention may be any shape; it is not limited to a circular shape characteristic of rotating disks.

Since with the new storage- device, the medium is stationary, expensive and failure-prone electro¬ mechanical rotational hardware is not required, nor is hardware required to move any heads. In some embodiments of the invention it may be desirable to provide mechanisms for adjusting the alignment of the medium slightly with respect to the heads, but that need only be done once when the medium is inserted into the device. Furthermore, problems of head an media wear and head crashes are eliminated with the invention. The foregoing description is limited to a specific embodiment of this invention. It will be apparent, however, that this invention can be practiced in systems having diverse basic construction or that use different internal circuitry than is described in the specification with the attainment of some or all of the advantages of this invention. Therefore, it is the object of the appended claims to cover all such variations as come within the true spirit and scope of this invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

Claims

1. A data storage device for use in a digital data processing system for storing digital data on a planar magnetic medium comprising magnetic head module means that includes a plurality of individually energizable read/write head means, each when energized generating a magnetic field, forming an array across one surface of said module means, the magnetic medium being adapted to be placed in juxtaposition with said surface of said module means such that when any head is energized a magnetic field is generated and a region of the magnetic medium proximate the head means is magnetized, said data storage device further comprising circuit means for selectively energizing selected ones of said head means to selectively magnetize the corresponding region of the medium with the direction of magnetization representing stored data.

2. A data storage device for use in a digital data processing system for storing digital data on a planar magnetic medium comprising opposing magnetic head module means and planar means having a retracted position to define a slot for receiving a planar magnetic medium, said planar means being biased towards a surface of said head module means to hold the magnetic medium in" juxtaposition with said surface of said head module means, said head module means comprising a plurality of individually energizable read/write head means, each when energized generating a magnetic field, forming an array across said surface of said module means such that when any head is energized a magnetic field is generated and a region of the magnetic medium proximate, the head means is magnetized, said data storage device further comprising circuit means for selectively energizing selected ones, of said head means to selectively magnetize the corresponding region of the medium with the direction of magnetization representing stored data.

3. A data storage device for use in a digital data processing system for storing digital data in a plurality of addressed storage locations on a planar magnetic medium comprising magnetic head module means that includes a plurality of individually energizable read/write head means, each associated- with an addressable location and comprising a head of magnetic . material surrounded by a winding of conductive material such that when an electric current is applied to the winding a magnetic field is generated in said head, said head means forming an array across one surface of said module means, the magnetic medium being adapted to be placed in juxtaposition with- said- surface of said module means such that when any head is energizad a magnetic field is generated and a region of the magnetic medium proximate the head means is magnetized thereby to store data in the addressed location, said data storage device further comprising circuit means for selectively energizing selected ones of said head means to magnetize the corresponding region of the medium with the direction of magnetization representing stored data, said circuit means including current source means for providing electric current in a selected direction, switch array means connected to said current source means and all of said winding means for selecting one of said head means for energization, and sense means connected to said current source means for sensing variations in the voltage during a read operation representing the value of data stored in the storage location associated^>with the address.

4. A data storage device as defined in any of claims 1 through 3 wherein each of said head means comprise a U- shaped head of magnetic material having an open end disposed toward the surface of said head module means in juxtaposition with the magnetic material and conductive winding means surrounding at least a portion of said head.

5. A data storage dev ice as def ined in claim 4 wherein said head compr ises a cross member hav ing depend ing legs to form a U-shape , sa id wi nd ing sur round ing the cross member.

6. A data storage device as defined in claim 4 wherein said head comprises a cross member having depending legs to form a U-shape, said winding comprising plural winding means each surrounding one of said legs,- and said circuit means providing energizing each of said winding means in opposing directions.

7. A data storage device as defined in claim 4 wherein a plurality of said head means are formed from an integral cross member means having depending therefrom a plurality of leg means, with pairs of leg means defining said head means.

8. A data storage device as defined in claim 7 wherein each said winding comprises a winding means around said cross member between each adjacent pair of leg means.

9. A data storage device as defined in claim 7 wherein each said winding comprises a winding means around each leg means, said circuit means energizing adjacent pair_, of winding means in opposing directions thereby to energize said head means.

10. A data storage device as defined in either of claims 1 or 3 in which said head means are supported on a surface of said magnetic module head means and said magnetic medium comprises a magnetic material formed over said surface and bound thereto.

11. A data storage device, as defined in claim 10 in which said magnetic medium is patterned to provide magnetic material only in juxtaposition to said head means.

12. A data storage device including a magnetic head module comprising a plurality of magnetic head means arrayed over a major" surface thereof and each head means having an energizable winding, the magnetic head module fabricated using a sequence of steps each using thin-film lithographic techniques to form a selected portion of the module and a further step of applying a layer of magnetic material over said major surface.

13. A data storage device as defined in claim 12 fabricated using the further step of patterning the magnetic material layer to leave magnetic material only in the regions of said major surface in juxtaposition to the head means.