EOT markers missing from 9 track tape...

The IBM System/360, released in 1964, introduced what is now generally known as 9 track tape. The ½ inch (12.7 mm) wide magnetic tape media and reels are the same size as the earlier IBM 7 track format it replaced, but the new format has eight data tracks and one parity track for a total of nine parallel tracks. We were sent seven of these tapes for recovery and conversion. With our unique tools and specially adapted tape drives we were able to extract the raw data and rebuild it back into the native format.

The drives wrote 9 tracks in parallel, one for each bit in an 8-bit byte, and one for parity. Originally, drives read and wrote at 800 bpi (bits per inch), but later generations sported densities of 1600, 3200 and 6250 bpi. The tapes themselves came in lengths of 800, 2400, and finally 3600 feet, yielding a maximum capacity of 260MB at 6250 bpi.

Every volume has beginning-of-tape (BOT) and end-of-tape (EOT) markers. These markers are pieces of photoreflective tape that delimit the writable area on a volume. ANSI magnetic tape standards require that a minimum of 14 feet to a maximum of 18 feet of magnetic tape precede the BOT marker; a minimum of 25 feet to a maximum of 30 feet of magnetic tape, of which 10 feet must be writable, must follow the EOT marker. The EOT marker indicates the start of the end of the writable area of the tape, rather than the physical end of the tape. Therefore, data and labels can be written after the EOT marker.

Using handlers that our developers have written specifically for converting this file type, together with specially adapted tape drives to overcome stiction and old delaminated tape, we were able to identify the end of each volume and write EOT markers. The data was then stripped out and copied to external hard drives before being returned to a very happy client!