Digital Magnetic Recording

Next to integrated circuits, magnetic recording represents one of the most important technological developments in modern times. The rise of low cost computing and the widespread availability of computers is directly linked to advances in recording technology. On this page are software tools related to magnetic recording in general, and links to related pages on this web site.

Data Storage and Retrieval

An overview of the sequence of events which occur in a digital magnetic recording device is shown in the figure below.

Overview of Digital Recording

The pages accessible in this part of the site are mainly concerned with those process steps which involve encoding, writing, reading, detection and decoding. Please note that the above diagram involves MFM encoding which has been supplanted by more efficient coding methods in modern drive. 

Actuator Analyzer

Screen Shot of Actuator Analyzer

This is a screen shot of an analyzer for 3.5in disk drive actuator assemblies. The user can provide the radius and skew angle at any two valid points and the software will calculate the radius vs skew for any o>ther valid radius. A closed form expression relating the radius and skew is used internally. A paper deriving the relevant geometric relations is available here. This application is useful in verifying actuator geometries and in determining skew angles for recording performance studies.

Heads and Media

Some useful tools for dealing with heads and media can be found  under Fields and Models. Here is a paper which examines the differences between models by Williams & Comstock and Neal Bertram. These models pertain to head/media optimization in general and the 'Q' function and transition length parameter 'a' in particular. An exact formula for the W&C 'Q' function and limiting values are also given.

Here are plots of the two functions.

Williams and Comstock Q Function

Bertrams' Q Function

Note that Bertram's Q function defines a family of curves, rather than a single plot.

Digital Recording Channels

On the channels page are a number of software tools and graphic signal simulations.


Several magnetic recording processes are modeled with animated graphics on the animation page.