ISO 7298:1985

Overview

ISO 7298:1985 - Information processing: Magnetic disk for data storage devices defines the mechanical, physical and magnetic characteristics for a lubricated magnetic disk of 210 mm outer diameter and 100 mm inner diameter intended to operate reliably at 158 368 flux transitions per track (often referenced as 158 000). Published in 1985, the standard sets environmental, dimensional, surface-finish and magnetic-testing requirements to ensure satisfactory performance at the specified track density. It also notes that other areal densities may require modified characteristics.

Key topics and requirements

• Scope & environment
  • Operating air temperature: 15 °C to 57 °C; relative humidity 8–80% (wet-bulb limits specified).
  • Air cleanliness: Class 100 (Annex A).
  • Ambient stray magnetic field limits to avoid data corruption.
• Dimensions & geometry
  • Inner diameter: 100.00 ±0.05 mm; outer diameter: 210.00 ±0.10 mm.
  • Concentricity, circularity and chamfering requirements to control unbalance and runout.
  • Clamping area and non‑magnetic zones defined for head flight and clamping.
• Physical characteristics
  • Thickness: ~1.905 ±0.025 mm.
  • Moment of inertia and rotational-stress capability (disk capable of withstanding up to 6 000 r/min).
  • Runout and axial limits (e.g., axial runout and velocity/acceleration test conditions).
• Surface and friction
  • Magnetic surface roughness: arithmetic average < 0.025 μm; maximum deviation limits and undulation amplitude (< 0.15 μm).
  • Clamping area finish: ≤ 0.8 μm average roughness.
  • Head/disk friction: average dynamic coefficient μm ≤ 0.200 (peak-to-peak Δμ ≤ 0.035) and static friction μs ≤ 1.0 after 48 h contact.
  • Minimum flying heights specified and discharge path to clamping area required.
• Durability & wear
  • Durability test: 10 000 head take-off/landing cycles with post-test read amplitude and head wear factor requirements (head wear factor < 1).
• Magnetic/testing requirements
  • Test track width: 40 ± 4 μm for test procedures (Annex C describes effective track width measurement).
  • Standard reference surfaces, test head calibration factors, overwrite and resolution specifications.
  • Test conditions for rotational frequency, stray-field limits, and measurement temperatures.

Applications and users

ISO 7298:1985 is primarily useful for:

• Magnetic disk manufacturers specifying disk geometry, coatings and lubrication.
• HDD and data-storage device designers validating head/disk interfaces and mechanical tolerances.
• Test laboratories and QA engineers performing runout, surface roughness, friction and durability testing.
• Procurement and compliance teams who need contract-level specifications for 210 mm media at high track densities.

Adhering to ISO 7298 helps ensure compatibility, reliability and predictable head/disk behavior at high areal densities.

Related standards

• ISO 1302 (surface texture indication) - referenced for surface finish specification.
• ISO/TC 97 (Information processing systems) - technical committee responsible for the standard.
• Annexes in ISO 7298: A (air cleanliness), B (head/disk friction test method), C (effective track width measurement) contain essential test procedures.