WO1999018570A1

WO1999018570A1 - A method and apparatus for providing enhanced transfer rate for a constant angular velocity storage disc

Info

Publication number: WO1999018570A1
Application number: PCT/IB1998/001417
Authority: WO
Inventors: Ronald Wilhelm Johan Saeijs
Original assignee: Koninklijke Philips Electronics N.V.; Philips Ab
Priority date: 1997-10-03
Filing date: 1998-09-14
Publication date: 1999-04-15

Abstract

For exchanging information with a constant angular velocity and trackwise organized storage disc, the invention provides an enhanced transfer rate in an external transfer stream. Segments are recurrently interleaved that are arranged at more than one radial track position at a relatively larger and at a relatively smaller than average radius value, respectively.

Description

A method and apparatus for providing enhanced transfer rate for a constant angular velocity storage disc.

BACKGROUND OF THE INVENTION

The invention relates to a method as recited in the preamble of Claim 1. Certain storage discs are operated with constant linear velocity (CLV), which allows for maximum storage density. Other storage discs are operated with constant angular velocity (CAV), which allows for immediate jumping between various radial positions without having to wait for adaptation of the rotary velocity. It has been found that both properties are advantageous from a user point of view.

SUMMARY TO THE INVENTION In consequence, amongst other things, it is an object of the present invention to provide a method as claimed in the preamble, wherein constant angular velocity can be combined with a maximum sustainable data rate. Now therefore, according to one of its aspects the invention is characterized according to the characterizing part of Claim 1. The invention also relates to an apparatus arranged for practising a method as recited, and to a storage disc arranged to be accessed according to such method. Further advantageous aspects of the invention are recited in dependent Claims.

BRIEF DESCRIPTION OF THE DRAWING

These and further aspects and advantages of the invention will be discussed more in detail hereinafter with reference to the disclosure of preferred embodiments, and in particular with reference to the appended Figures that show: Figures 1A, IB, the general layout diagram of a CLV disc; Figure 2, an apparatus for use with such a disc; Figure 3, a multi-head player according to the invention; Figure 4, a preferred interleave diagram.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Traditional disc storage systems such as standard Compact Disc and its derivatives have used rotation with constant linear velocity inasmuch as they were generally oriented to linear recording and playback. Here, the rotary speed of the disc will be adapted to the radial position of the access unit, so as to obtain a uniform linear velocity on the disc. Newer applications, such as in the field of multimedia, and more in particular, in a read- write environment, would use multiple jumps between track positions without loosing time by adapting the rotary speed of the disc. Here, the rotary speed will remain the same, so that linear velocity at the access unit is substantially proportional to the actual radius value. If the tangential data density per unit of track length is uniform, this would imply a transfer rate that is a linear function of the radius.

Figures 1A, IB, show the general layout diagram of a storage disc in two versions. In Figure 1A the track is organized as a single spiral. The standard access direction may be clockwise, in which case the start of the track is at the innermost radius, and the disc itself will rotate counter-clockwise. The inverse situation is equally useful. Further, the storage could be organized according to more than one spiral. In Figure IB, the track is organized as a sequence of circles. Both directions of the rotation, with starting at the largest as well as at the smallest diameter are feasible; generally at the end of each rotation, a jump to a new track is executed. According to the CD standard, the smallest radius is 24 millimetres and the largest is 58 millimetres, which have a ratio of 1:2.4, so that minimum to average has a ratio of 1: 1.7. Now a somewhat conservative prognosis foresees a data rate in the order of 10⁷ bits per second related to a single head that continuously accesses the track. For optical access, the storage mechanism may be phase-change, wherein the disc material may change reversibly between crystalline and amorphous states. In particular, this mechanism causes an upper bound for the access velocity, because the transition cannot be arbitrarily fast. Another feasible access procedure is through the magneto-optical effect, wherein the optical access actually detects a local micro-magnetic field. Now, if the user data in such system is recorded in contiguous locations, the sketched organization implies that the sustainable data rate depends on the radius: on a systems level this maximum rate then corresponds with the smallest value for the radius. According to the invention, the maximum sustainable data rate is determined by the average value of the radius, which is realized in a near optimal manner, so that the maximum user data rate will theoretically be increased by a factor of 1.7. Alternatively, the rotary speed of the disc may be decreased by this same factor, while furthermore, various trade-offs are feasible. The idea of the invention is to recurrently interleave data segments that are arranged at more than one radial track position at a relatively larger and at a relatively smaller than average radius value, respectively. Together they will be substantially equal to the average radius. In this way segments with more than average transfer speed will be interleaved with segments that have less than average transfer speed. In between segments, a read-write unit will physically jump from one radius value to another. In practice, a disc may be driven at 10-100 revolutions per second, so that a single revolution will take 10-100 millisecs. The time to jump is variable, in that it depends on the jump distance, and may lie between a small value if the jump is a few track-to-track distances only, and may have a worst case value in thew order of some 500 milliseconds. If the dead time should account only to 10%, the jumps may occur no more often than every few revolutions. Further dimensioning may be set according to actual needs. A simple and effective manner to realize the above principle is by a priori dividing the disc into pairs of segments in such a way that:

- the total amount of data in a pair of segments is substantially uniform over the pairs;

- the average radius of the two segments of a pair is substantially equal to the average disc radius; - the relative sizes of the segments in a pair is such that their relative transfer times are substantially equal.

Both the recording and the playback of the data will now be done pair after pair, with the two segments of each pair following each other contiguously. A simple organization is to set the segment size on an integer number of revolutions, pairing the outermost n revolutions with the innermost n revolutions, and so on. Of course, the storage segments may combine with further organizations of the data that relate to the actual content, or for example to an error correction (ECC) organization. The granularity caused by the latter features may be finer as well as coarser than the storage segments. Furthermore, the organization may be optimized, so that the first of the three above conditions will be satisfied exactly, and the other two only to an acceptable degree. In roughly similar manner, groups of larger numbers of segments may be formed, that effect about the same advantages. In order to reduce the average amount of jump time, the ordering of segments within a pair may be optimized as follows. First divide the total set of pairs into two equal-sized subsets called even pairs and odd pairs, respectively. Define the recording/playback order of the two segments in a pair depending on whether the actual pair is odd or even. For example, in an odd pair the innermost segment will lead, whereas in an even segment the outermost segment will lead. In this case a general strategy may be to generally alternate between odd pairs and even pairs during either recording or playback. As a result of this rule, two consecutive pairs will together cause at worst one complete movement from the inner radius to the outer radius in a sequence of one to three jumps in the same direction, followed by one complete reverse movement in three to one jumps, all in the opposite direction. The total number of jumps for accessing an arbitrary pair is of course equal to four. It may be shown that this will reduce the worst-case average jump time as compared to the general case where each single pair may cause a complete movement from inside to outside and back. The assigning as even or odd pairs may be done on a contingency basis. Figure 4 shows a preferred interleave diagram relating to such pair. Furthermore, in Figure IB capital A indicates the locations of a first pair of segments, whereas capital B indicates the locations of a second pair of segments. In principle, the strategy discussed will be advantageous in magnetic disc storage technology, in particular, for use in multimedia applications.

Figure 2 shows an apparatus for use with a disc according to the invention. As shown, there are two head positions 20, 22, that may represent the two actual access positions of a single head assigned to a particular segment pair as discussed supra, or according to a solution on another level of sophistication. As will be described hereinafter, there may alternatively be two physically distinct heads. Data interconnection to the head(s) is represented by numerals 32, 34, and positioning control(s) by numerals 21, 23. Block 24 represents the access timing and data (de) multiplexing as far as applicable. Block 26 represents a storage buffer that may be used as intermediate between internal and external requirements. Block 28 represents an external interface means that may comprise various further processing facilities such as error protection, data compression-expansion and reformatting. Overall control is represented by block 30 that may effect data synchronizing on bit, byte, segment or other level, execute storage management, and control the access head position(s). For this purpose it further communicates with blocks 24, 26 and 28. Figure 3 shows a multi-head player according to the invention. Disc 40 is accessed through heads 42, 44 shown as dots. The idea of this embodiment is to record user data by two heads that are respectively assigned to the inner parts and outer parts of the disc, respectively. Inner segments and outer segments are recorded simultaneously, where pairs are located in such manner that the average radius for the pair is substantially constant, and substantially equal to the average radius of the available disc part. Hence, during accessing, a segment with less-than-average transfer rate (smaller than average radius) is combined with a segment with more-than-average transfer rate (larger than average radius). The total transfer rate then will be substantially uniform and constant, and will be reached through effective (de) multiplexing. In the Figure, the arrow indicates the direction of the head(s) motion. It is possible to effect this in the set-up of Figure 2 with two fully independent heads. Alternatively, the two heads may share a single mechanical slider for coarse positioning, and have separate electromechanical actuators for finer positioning and for track-following. By itself, such slider-and-actuator mechanism applied to a single head is standard. In particular when using a spiral track, the radius variation along a single revolution may differ between the two heads. Radial differences in the order of magnitude of the inter- track distance are however ignored for determining average radius values. Also, the plural-head facility may be used with magnetic disc storage, in particular for use in a multimedia environment.

Claims

CLAIMS:

1. A method for exchanging information with a constant angular velocity and trackwise organized storage disc, said method being characterized by for providing an enhanced transfer rate in an external transfer stream, recurrently interleaving segments that are arranged at more than one radial track position at a relatively larger value and at a relatively smaller value than average radius value, respectively, and the average value of said larger and smaller values being uniform and substantially equal to an average radius value of an available disc area.

2. A method as claimed in Claim 1 , wherein said interleaving is at least effected in part through physical head jumping between outer and inner track positions.

3. A method as claimed in Claim 2, wherein storage is organized in groups of a uniform and even number of segments, wherein the various groups have a substantially uniform amount of data, and the segments within a group are transferred contiguously in time.

4. A method as claimed in Claim 3, wherein said groups are pairs.

5. A method as claimed in Claim 4, wherein of a sequence of pairs, alternate pairs have their low-radius segment and their high-radius segment accessed first, respectively.

6. A method as claimed in Claim 1, wherein said interleaving is effected through logical (de)multiplexing among at least a first access head at an outer position and a second access head at an inner position.

7. A method as claimed in Claim 6, wherein said first and second heads are mechanically interlinked for gross positioning and mechanically separate for fine positioning.

8. A method as claimed in Claim 6, wherein the number of heads is exactly two per disc surface.

9. A method as claimed in Claim 1 for use with an optical disc.

10. A method as claimed in Claim 9 for use with a read -write disc.

11. A method as claimed in Claim 1 for use with bidirectional access.

12. An apparatus arranged for practising a method as claimed in Claim 1.

13. A storage disc containing stored information and being characterized by for providing an enhanced transfer rate in an external transfer stream, having recurrently interleaved segments that are arranged at more than one radial track position at a relatively larger and at a relatively smaller than average radius value, respectively, and the average value of said larger and smaller values being uniform and substantially equal to an average radius value of an available disc area.