Abstract: A direct access storage device (DASD) system uses a read/write head having a wide transducer write element and a narrow magneto-resistive read element. In order to avoid mistakenly reading a incompletely erased old data field, the system uses a verification procedure. Data are read at two positions along the data track which are separated by a radial distance D. This distance D is selected to be greater than the width of any incompletely erased data record. If the data read at the two read positions are equal, then the data are deemed to be correct and are sent to a host system.

Abstract: A process for oxidation of a tetrahydro compound of the formula ##STR1## wherein R and R' independently are H, alkyl, aryl or halo, to a glycol of the formula ##STR2## comprises treating the tetrahydro compound with hydrogen peroxide at an elevated temperature under reflux conditions in the absence of a catalyst. The thus-formed glycol can be further oxidized to a butanetetracarboxylic acid of the formula ##STR3## with hydrogen peroxide in the presence of a catalyst selected from the group consisting of a manganese salt, an iron salt, a chromium salt, a cerium salt, a persulfate, a perborate, a silicate, tungstic acid or an ammonium or alkali metal salt or heteropolyacid thereof, or molybdic acid or an ammonium or alkali metal salt or heteropolyacid thereof.

Abstract: A process for oxidation of a tetrahydro compound of the formula ##STR1## wherein R and R' independently are H, alkyl, aryl or halo, to a glycol of the formula ##STR2## comprises treating the tetrahydro compound with hydrogen peroxide at an elevated temperature in the absence of a catalyst.The thus-formed glycol can be further oxidized in a butanetetracarboxylic acid of the formula ##STR3## with hydrogen peroxide in the presence of a catalyst selected from the group consisting of a manganese salt, an iron salt, a chromium salt, a cerium salt, a persulfate, a perborate, a silicate, tungstic acid or an ammonium or alkali metal salt or heteropolyacid thereof, or molybdic acid or an ammonium or alkali metal salt or heteropolyacid thereof.