Computer Memories Inc. (CMI) was a manufacturer of hard disks during the early 1980s. They became infamous in 1985 when it was found that they'd shipped a large quantity of defective 20-megabyte hard disks to IBM for the base model of the IBM PC/AT, a result of IBM attempting to low-cost the drive. Later, it was found that the entire CMI 6600 line of drives infringed on a patent owned by Quantum Corporation, related to the servo system the drives used; instead of putting the tracking grating on the head arm and driving the arm directly from a voice coil, like the Quantum designs, CMI made a composite motor that would bolt to the drive in place of the usual stepper motor, with the voice coil on the bottom and the tracking mechanism on top (similar to DC servo motors used in process controls and robotics). CMI connected the motor to the arm with a metal-band pulley, the same mechanism they used on their stepper-motor drives. Since the feedback system was behind the pulley, it had to compensate for slack in the arm, one of several things the CMI firmware didn't take account of. Typical hard drives of the mid-1990s. ... This article is about the year. ... A megabyte is a unit of information or computer storage equal to approximately one million bytes. ... For other uses, see IBM (disambiguation). ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... Quantum Corporation is a manufacturer of tape drive products, based in San Jose, California. ... Voice coil originally described the coil of copper wire mounted to the moving cone of a loudspeaker. ...

CMI would never recover from the IBM incident, and eventually left the hard disk business (after releasing a "patent-free" 7600 series of drives) in 1986. 1986 (MCMLXXXVI) was a common year starting on Wednesday of the Gregorian calendar. ...

Before the IBM incident, CMI made basic stepper motor-based drives, with low cost in mind. They merged with a competitor, IMI, in 1982. The top electromagnet (1) is charged, attracting the topmost four teeth of a sprocket. ...

External links

• "Megabyte Tarnish" magazine article from September 1985 PC Australia, accessed June 17, 2006