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Providing Security Erasure of a Deleted Disk or Disk Document

IP.com Disclosure Number: IPCOM000046080D
Original Publication Date: 1983-May-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Chou, JK: AUTHOR [+4]

Abstract

A programming procedure is provided to insure the complete erasure of previously used disk or disk documents. Such complete erasure insures that the information on the disk cannot subsequently be recreated. Two functions are described: a clear/initialize function to remove the contents of the entire disk and a delete document function to remove the contents of a single document.

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Providing Security Erasure of a Deleted Disk or Disk Document

A programming procedure is provided to insure the complete erasure of previously used disk or disk documents. Such complete erasure insures that the information on the disk cannot subsequently be recreated. Two functions are described: a clear/initialize function to remove the contents of the entire disk and a delete document function to remove the contents of a single document.

The clear and initialize operation causes an appropriate volume label to be written onto the system track of the disk. A volume table of contents (VTOC) buffer is built where the first and 129th bytes are delimiters and the remaining bytes are zero. A usage map is then written in the system area. For every sector in the data area, a hexadecimal X'AA' is written to every data byte. Thence, a hexadecimal X'55' is written to every data byte not in the data area.

This insures that the contents of every potential data sector is erased by changing the magnetic flux in every sector twice. The routine for accomplishing the foregoing is described in Fig. 1.

It is understood that a disk document contains five important items: a header record label, Type 1 (HDR1); one or more header labels, Type 3 (HDR3); a disk usage map; a volume table of contents (VTOC) usage map; and an entry in the disk information block (DIB). To delete a document, these five items must be cleared. Thus, the system first causes the DIB entry to be cleared and the HD...