System and method for emulating disk tracks to maintain data format compatibility

A disk track emulation system in a disk control device, for maintaining compatibility between different data formats, said system comprising:

• said disk control device connected between a host device and a disk device;
• said host device handling data in accordance with a first variable track length data format, and said disk control device and said disk device handling data in accordance with a second variable track length data format, said second data format different from said first data format;
• said first data format including cells each consisting of n bytes, N number of cells being on one circumferential track of said first data format;
• said second data format including cells each consisting of m bytes, M number of cells being on one circumferential track of said second data format;
• wherein N is unequal to M and n is unequal to m;
• the data in accordance with said first data format including, for each track to be emulated, a first home address indicating at least a logical position of the track and a first count area indicating at least a logical position of a record in the track,
• the data in accordance with said second data format including, for each track on said disk device a second home address indicating at least a physical position of the track on said disk device and a second count area indicating at least a physical position of a record in the track,
• wherein:
• said second data format further including a physical cell position data including the physical cell position of a track and a record on said disk device to be accessed, and a logical cell position data used in said host device and indicating the logical cell position of a track and a record on said disk device to be accessed and corresponding to said physical cell position.

A disk track emulation method for maintaining a compatibility of a variable length data format of a new disk track with a conventional variable track length data format, by using a new disk track device having disk tracks with a data format different from that of a conventional disk device, and by means of a disk control device for controlling the new disk device, wherein:

• using the characteristics that said data formats are divided by a unit called a cell, said conventional data format cells and said different data format cells having a constant and unequal number of bytes;
• said conventional data format including cells each consisting of n bytes, N number of cells being on one circumferential track of said conventional data format;
• said different data format including cells each consisting of m bytes, M number of cells being on one circumferential track of said different data format;
• wherein N is unequal to M and n is unequal to m;
• and
• writing, into both a home address area and a count area in the new data format, track and record cell position data with the different data format, and compatible track and record cell position data with respect to the active data format in which the compatibility should be maintained, whereby the compatibility of the data format is maintained.

A disk track emulation system for making a first variable track length data format used by a host device compatible with a second variable track length data format used by a disk device;

• said first data format including cells each consisting of n bytes, N number of cells being on a circumferential track of the first data format;
• said second data format including cells each consisting of m bytes, M number of cells being on one circumferential track of the first data format;
• said m number being different than said n number;
• said system comprising:
• said host device, said disk device, and a disk control device with a physical cell position register in which physical cell position information is stored, and an aligned cell position register in which logical position information is stored connected between said host device and said disk device;
• said disk device including at least one disk track having a plurality of cells, each of said cells having a certain number of bytes;
• said host device handling data in accordance with said first data format, and said disk control device and said disk device handling data in accordance with said second data format;
• said disk control device comprising:
• physical cell position data generating means for generating physical cell position data representing a position of a track and a record of a cell to be accessed in accordance with said second data format using said physical cell position data in said physical cell position register, in response to accessing operations by said host device, said disk control device, and said disk device;
• logical cell position data generating means for generating logical cell position data representing a position of a track and a record of the cell to be accessed in accordance with said first data format using said logical cell position data in said logical cell position register;
• and
• said disk control device storing said physical cell position data and said logical cell position data on said disk track in accordance with said second data format.

A disk track emulation method for maintaining a compatibility of a variable length data format of a new disk track with a variable track length conventional data format, by using a new disk track device having disk tracks with a data format different from that of a conventional disk device, and by means of a disk control device with a physical cell position register in which physical track and record cell position information is stored, and logical cell position register in which logical track and record cell position information is stored for controlling the new disk device,

• said emulation method using the characteristics that said data formats are divided by a unit called a cell, said conventional data format cells and said different data format cells having a constant and unequal number of bytes;
• said conventional data format including cells each consisting of n bytes, N number of cells being on one circumferential track of said conventional data format;
• said different data format including cells consisting of m bytes, M number of cells being on one circumferential track of said different data format;
• wherein N is unequal to M and n is unequal to m;
• and
• writing, into both a home address area and a count area in the different data format, cell position data with the new data format, and compatible cell position data with respect to the active data, whereby the compatibility of the data is maintained.