Abstract: In a data recording system used for a magnetic disk drive, a write amplifier feeds a write head with a recording current that corresponds to the data to be recorded on the disk. A recording current controller selects a current value to be fed to the write head from the write amplifier according to the recording pattern detected by a pattern detection circuit. Thus, an effective recording track width can be selected without relying on the recording wavelength of the data to be recorded. Therefore, the influence of the cross talk from adjacently located tracks can be effectively reduced without unnecessarily reducing the recording track width.

Abstract: In a copying machine of the type comprising an image projecting lens movable in a direction of an optical axis thereof for varying a magnifying power, a reflecting mirror interlocked with the lens for effecting focusing, and two groups of light sources for illuminating a manuscript, there is provided an exposure control system comprising variable resistors driven by the projecting lens, oscillators for generating pulse signals of frequencies varying in accordance with resistance variations of the variable resistors and with a variation in a source voltage, counters counting the number of the pulse signals in accordance with an exposure index, and switch means for lighting the light sources during intervals determined by an exposure index.