Static information storage and retrieval – Read/write circuit – Having particular data buffer or latch
Patent
1983-12-29
1987-09-01
Fears, Terrell W.
Static information storage and retrieval
Read/write circuit
Having particular data buffer or latch
371 13, G11C 1300
Patent
active
046912991
DESCRIPTION:
BRIEF SUMMARY
The invention relates generally to a method and apparatus for writing in data storage systems and in particular to a method and apparatus for writing in a non-erasable storage medium such as a digital optical disk or paper tape.
BACKGROUND OF THE INVENTION
Non-erasable, or write-once, data storage media such as digital optical disks, paper tape, PROMS, etc., have a plurality of bit positions, each of which can be irreversibly changed from an original state to a new state but one time. Thus, typically, the initial state of the bit position is designated a "zero" and the "zero" can be overwritten with a "one" when data is written into the media. Once the data has been written in a section of the media, which may be all of the media, that section is considered to be "used" by those experienced in the field, and is not considered to be reusable thereafter for recording new data.
Some non-erasable media, notably digital optical disks, can store vast amounts of data. A single twelve-inch disk can be used to store over 10.sup.11 bits of data, the equivalent of forty reels of magnetic tape, and access can be provided to any of it in about one-tenth of a second. This is an order of magnitude improvement in the cost/performance of memory technology and has had dramatic effects. And, while the cost of a high capacity, single twelve-inch disk may be only $100, that high capacity and low cost are achieved only at the further philosophical cost of making the writing process irreversible.
Similar limits exist, and are probably more familiar, in connection with the non-erasable media, such as punched paper tape, punched cards, and programmable read only memories (PROMS). However, the tremendous capacity and low cost per bit of digital optical disks provides a strong motivation for more closely examining their one drawback, the non-erasable nature of the memory storage process.
Therefore a primary object of this invention is an apparatus and method for reusing, that is writing more than once in, non-erasable memories. Other objects of the invention are an apparatus and method for reliably and simply increasing the effective capacity of non-erasable memories, and for providing a simple, easily implemented apparatus and method for rewriting in an otherwise non-erasable memory.
SUMMARY OF THE INVENTION
In one aspect, the invention relates to apparatus for reusing a non-erasable memory medium. The apparatus features reading circuitry for reading successive groups of digits from the non-erasable memory medium and a process element for writing over each of the successive groups in accordance with both the input data information read at each successive group and respectively new incoming input-data information. Thus, the process element provides an output in accordance with a predetermined "mapping" procedure or plan which is determined by the two data information sources received above. Thereafter, the "written over" groups of digits can be uniquely read, at a later time, to reproduce the just written new incoming input-data information.
In another aspect, the invention relates to apparatus for writing a plurality of times in a non-erasable memory. The invention features receiving circuitry for receiving incoming digital data and for forming sequential input-data groups from the received data. A reading element reads successive groups of digital data from successive groups of data positions in the non-erasable memory. In response to each formed sequential input-data group and a respective read successive data group from memory, mapping circuitry generates successive new coded groups of digital data. Writing circuitry sequentially writes each of the coded groups of digital data over the corresponding read data group. Thereby, the coded groups of data can be later read and uniquely decoded to generate the previously received incoming digital data. Depending upon the coding or mapping method, the non-erasable medium can be rewritten a substantial number of times.
In yet another aspect, the invention relates to a method for wr
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Jones et al., "Read-Only Programmable Logic Array with Writable Segment", IBM Tech. Dis. Bul., vol. 17, No. 10, Mar. 1975, p. 2987.
Goldstein, charles M.; "Optical Disk Technology and Information"; Feb. 1982; Science, vol. 215; pp. 862-868.
Rivest Ronald L.
Shamir Adi
Fears Terrell W.
Massachusetts Institute of Technology
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