An analytical estimation of the date replacement method for optical disk media is discussed. A modified Gilbert model is introduced to describe the bit-error occurrence in the reproduction process. This model deduces the defect-relief probability required to estimate the efficiency of a date replacement method.

A new positioning method for higher track density hard disk using embossed-servo-mark magnetic disks is proposed. An embossed-servo-mark medium with grooved-guard-band data tracks for 208 TPMM was developed using molded plastic substrate. The marks were magnetized so that conventional magnetic head can reproduce position signals. Simple analogy from optical disk track following to magnetic disk track following was taken and examined. A DSP controlled feed-forward servo was introduced to resolve the inherent eccentricity caused by mounting preformed tracks onto an independent spindle axis. The prototype drives with a form factor of 2.5 inches were designed introducing the disks, the servo scheme and the newly developed orthogonal MR head. As a result, an areal density of 650 kbits/mm2 (about 420 Mbits/in2) recording was successfully demonstrated on the media using 2.5-inch form factor prototype drives.

A dynamic measurement method of static R/W skew caused by MR-Inductive element alignment error is discussed. A geometrical model for the displacement between a write gap and a read gap on a swing arm is formulated. A measurement method wthich employs read-after-write procedure on disk surfaces in a drive is proposed. A simulation results is reported. It contributes to increase the track densities of HDDs using MR/Inductive heads in the region of more than 200 TPMM (5000 TPI).

A method of quick displaying documents stored in electrical filing systems is discussed. The index codes generated automatically when the pictures of an original page are stored, can be decoded to full-page-size rough pictures on the CRT display. The pages are reconstructed at a maximum speed of nearly 20 pages per second. This method makes it possible to quick look over the pages in the image-coded document filing system.

A new 90-mm magneto-optical disk subsystem has been developed. It features a rewritable 100-Mbyte disk, a half-height drive and a highly reliable controller. Its effective data transfer rate is 330 kbytes/second, its average access time is 100 ms, and its data error rate is less than 10-12 events/bit. This subsystem uses a novel design method based on the media's physical characteristics. This method employs a statistical model to describe error occurrences. It considers the dimensional characteristics of media defects by analyzing the reproduced signal. Using this design method, the error control strategy, which consists of a defect management scheme and an error-correcting procedure, is determined. Furthermore, this subsystem uses a new physical media format called Discrete Block Format. Optical read-only madia compatibility can be obtained quite easily with this format. The subsystem can be used with personal computers, communication terminals and measuring instruments.

A performance evaluation of various sector alternation methods for optical disks is discussed. The alternation frequency and defect-proof effects are described quantitatively for alternation methods. This evaluation makes it clear that the group alternation method of the on-the-fly alternation methods is suitable for high speed data processing operations.

A method of domain attribute identification for automated document storage devices is discussed. Only run-length parameters are used to identify the attribute of a domain on a page. This method makes it possible to obtain indexes of every page automatically and to reconstruct an abbreviated picture quickly in the image-coded document filing system.

An experimental relationship between byte-organizations and byte-error characteristics for optical disks is discussed. A two-dimensional byte-organization is proposed to decrease byte-errors, based on measured results. This byte-organization is effective in parallel-track recording.