Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the record
Patent
1992-03-06
1994-12-27
Psitos, Aristotelis
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the record
3606721, G11B 1548
Patent
active
053770560
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a digital data tape reading device. Data is stored by magnetic, optical or magnetic-optical techniques on disks. For large amounts of data, tape is a more convenient storage medium physically. Only magnetic techniques are used currently for tape storage, although other techniques can be envisaged.
In order to read or write data the storage medium (disk or tape) must be moved relatively to a read/write head arrangement. Repositioning with respect to the head arrangement is frequently necessary and in the case of tape devices, repositioning means stopping and restarting the tape. Repositioning causes wear of the tape drive mechanism and should be kept to a minimum. Repositioning is necessitated by differences in the data transfer rate of equipment to or from which the tape data is being supplied. Thus, a computer coupled to a tape storage device may have an inherent data transfer rate which is permanently less than the native transfer rate of data to or from the tape, or the computer data transfer rate may fluctuate because of other demands made on the computer processor.
Temporary fluctuations in relative data transfer rates may be handled by an electronic buffer between the computer and the tape device, the buffer being capable of accepting and feeding out data at differential rates. Permanent differences between the computer data transfer rate and the native tape data transfer rate will cause the buffer to empty or fill, depending on the direction of data flow. Then repositioning would normally become necessary. In order to avoid this when writing to tape it has been proposed to allow the tape to continue to run and to write to the tape, while awaiting the arrival of more data, "amble" tracks which include no data. The "amble" tracks are ignored when the tape is read.
The present invention, on the other hand, addresses the problem of reading data from a tape into equipment having an inherent data transfer rate which is lower than the native data transfer rate of the tape.
SUMMARY OF THE INVENTION
According to the invention there is provided a digital data tape reading device for reading data from a tape and supplying the data to equipment, the device comprising a read head arrangement and tape motor mechanism for moving the tape past the read head arrangement; an electronic buffer which is filled by data as it is read from the tape and which is emptied of data as it is fed to the equipment; and tape control equipment responsive to the data level in the buffer to stop the tape and reposition the tape with respect to the read head arrangement, the tape control equipment including means: restart position to which the tape must next be repositioned, this tape position corresponding to the head of a portion of data to be next fed to the buffer, hereinafter referred to as the new data; signal, without reading data; commence reading data to the buffer from the current tape position, which data is the tail of the new data; the tape to the restart position; buffer; and
While the invention is applicable to data tapes recorded in many different formats, the preferred format is the digital data storage (DDS) format which is described in the document "Digital Data Storage Format Description" (Revision B, October 1988) available from Hewlett-Packard Limited, Bristol, England. In this format the head arrangement is a helical-scan arrangement and data is recorded on the tape in discrete groups. Each aforesaid portion of new data is preferably a complete group. By using the invention one more group is read per reposition cycle and this has a significant effect in reducing the number of repositions in DDS drives where the buffer can hold only a small number of groups.
BRIEF DESCRIPTION OF DRAWINGS
The invention will further be described with reference to the accompanying drawings, of which:
FIG. 1 is a block schematic diagram of a digital tape reading device embodying the invention;
FIG. 2 is a graph illustrating buffer utilisation in a prior art digital tape read
REFERENCES:
patent: 4821129 (1989-04-01), Culp
Hewlett--Packard Company
Psitos Aristotelis
Wilson James T.
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