James Howard Eaton

Timing-based track-following servo for linear tape systems

Timing-Based Servo (TBS) is a unique servo technology developed specifically for linear tape drives. In TBS systems, recorded servo patterns consist of transitions with two different azimuthal slopes, and head position is derived from the relative timing of pulses generated by a narrow head reading the pattern. Position signals are nearly perfectly linear over multiple track widths, and highly immune to errors caused by head wear, head instability, debris, and media defects. Multitrack TBS servo patterns are written in a single pass using a novel multigap horizontal thin film servo writing head. The design of the pattern and its dimensions are optimized to provide sampling rate, noise level, and error rate suitable for the intended application. An all-digital TBS servo channel provides a speed-invariant position signal. Pattern recognition algorithms detect servo signal errors, providing a highly robust servo signal. Test results show approximately I pm linearity and 0.3 /spl mu/m noise level over a width of 400 /spl mu/m width with 18 kHz sampling rate. The TBS pattern allows flexibility for encoding additional information without affecting the position signal. By shifting transitions as little as 0.1 /spl mu/m from their nominal pattern positions, a low error rate serial bitstream can be encoded in the servo track. This technique allows tape longitudinal position to be encoded with a resolution of about 2 mm, allowing efficient and precise tape transport control based on the servo signal alone.

Six orders of magnitude in linear tape technology: The one-terabyte project

For the last 50 years, tape has persisted as the media of choice when inexpensive data storage is required and speed is not critical. The cost of tape storage normalized per unit capacity (dollars per gigabyte) decreased steadily over this time, driven primarily by advances in areal density and reduction of tape thickness. This paper reports the next advance in tape storage--a demonstration of a tenfold increase in capacity over current-generation Linear Tape-Open® (LTO®) systems. One terabyte (1 TB, or 1000 GB) of uncompressed data was written on half-inch tape using the LTO form factor. This technical breakthrough involves significant advances in nearly every aspect of the recording process: heads, media, channel electronics, and recording platform.

Hard-disk-drive technology flat heads for linear tape recording

IBM thin-film tape heads have evolved from the ferrite-based heads first used in the IBM Model 3480 Tape Drive to the hard-disk-drive (HDD) technology flat-profile heads used in IBM Linear Tape-Open® (LTO®) products. This paper describes that transition and discusses the flat tape head manufacturing processes, drive implementation, performance, and outlook. Thin-film head technology for hard-disk drives was first used in tape heads in the early 1990s, when IBM built quarter-inch cartridge head images on HDD-type wafers. This was a springboard for the next step, flat-lapped tape heads, which use not only HDD wafers, but also HDD post-wafer machining technologies. With the emergence of LTO, flat heads entered mainstream tape head production in IBM. These have proven to have high performance and durability.

Flat profile tape recording head

In conventional recording, tape wraps a cylindrically contoured head. The authors describe an implementation in which tape contacts a flat-profile bidirectional recording head. Magnetic transducers are located away from the air-scraping edges in the region of uniform head-tape spacing. Optical measurements on glass heads confirm intimate contact between head and smooth media below approximately 3 m/s. Wallace spacing losses show an increase with tape speed, but contact is still evidenced by head wear at 6 m/s. Air leakage and tape mechanical effects lift the tape edges. The width of the lost-contact region is controlled by the design. Flat heads are fabricated using hard-disk-drive head materials, methods, and facilities, and are implemented in the IBM TotalStorage 3580 Linear Tape Open Ultrium drive.

Microtrack profiling technique for narrow track tape heads

Microtrack properties of magnetoresistive (MR) tape heads are difficult to measure with conventional microtrack profiling techniques. The authors present a technique for rapid and dynamic measurement of these profiles for tape heads as narrow as 5 mu m using a 5 mu m-wide write head translated on a sinusoidal trajectory. The authors have used this technique on two types of tape heads, one where the only longitudinal bias is due to the shape anisotropy and one where exchange bias elements are used for end stabilization. These profiles give insight into the domain structure of the sensor and can be used as a diagnostic tool to predict head Barkhausen noise levels. >