System to demonstrate and sell computer programs

We claim:

1. A vending system for retailing at least one computer program comprising:

a retailed computer program;

a transmitting unit including means for repetitively transmitting said retailed computer program;

a medium of transmission comprising cable television cable, said transmission medium being in communication with said transmitting unit and carrying said retained computer program repetitively transmitted by said transmitting unit, said transmission medium simultaneously carrying other signals comprising television signals;

a plurality of computing devices located in domiciles, each of said computing devices including a receiver in communication with said transmission medium, each of said receivers being able to access and receive said retailed computer program repetitively transmitted by said transmitting unit through said transmission medium, and each of said computing devices comprising a processing section able to execute said retailed computer program to provide trail use of said retailed computer program to users of said computing devices in their domiciles, said trial use providing full use of said retailed computer-program;

a vending program transmitted through said transmission medium to said computing devices, each of said computing devices being able to execute said vending program to provide means for said users of said computing devices to purchase reusable copies of said retailed computer program in their domiciles, said reusable copies of said retailed computer program being adapted for use on one of said computing devices; and

said vending system including means to prohibit unauthorized duplication of said retailed computer program.

2. The vending system of claim 1, wherein said transmitting unit repetitively transmits a plurality of retailed computer programs through said transmission medium to said plurality of computing devices, and wherein said computing devices are capable of executing said plurality of retailed computer programs.

3. The vending system of claim 1 wherein said computing devices comprise a personal computer as processing apparatus.

4. The vending system of claim 1 wherein said computing devices comprise, as processing apparatus, an entertainment computing device utilizing replaceable read-only memory cartridges that provide game functions.

5. A vending system for selling computer programs comprising:

a retailed computer program;

a transmitting unit for repetitively transmitting said retailed computer program;

a medium of transmission, said transmission medium being in communication with said transmitting unit, and said transmission medium carrying said retailed computer program repetitively transmitted by said transmitting unit;

a computing device in communication with said transmission medium, said computing device including receiving apparatus to receive said retailed computer program from said transmission medium and having processing apparatus able to execute said retailed computer program repetitively transmitted through said transmitting medium,

said computing device being located in a domicile to provide trial use of said retailed computer program to a user of said computing device in the user's domicile, said trial use providing complete use of said retailed computer program;

a vending program transmitted through said transmission medium to said computing device, said computing device being able to execute said vending program to provide means for said user of said computing device to purchase reusable copies of said retailed computer program in the user's domicile; and

said vending system including means to prohibit unauthorized duplication of said retailed computer program.

6. The vending system of claim 5 wherein said transmission medium comprises cable television cable.

7. The vending system of claim 5 wherein said transmitting unit repetitively transmits a plurality of retailed computer programs through said transmission medium to said computing device.

8. The vending system of claim 5 wherein said computing device comprises, as said processing apparatus, a personal computer.

9. The vending system of claim 5 wherein said computing device comprises, as said processing apparatus, an entertainment computing device utilizing replaceable read-only memory cartridges that provide game functions.

10. The vending system of claim 5 wherein said receiving apparatus of said computing device is not integral with said processing apparatus of said computing device.

11. The vending system of claim 5 wherein said transmission medium is a common carrier medium.

12. The vending system of claim 5, comprising a plurality of said computing devices,

13. A method of protecting demonstrated retailed computer programs from unauthorized duplication comprising the steps of:

repetitively transmitting a retailed computer program through one-way media to a computing device, such that said computing device executes routines in said retailed computer program and a user of said computing devices has full use of said retailed computer program, and such that said computing device at no single time has a true, accurate and complete copy of said retailed computer program within said computing device, thereby preventing unauthorized duplication of said retailed computer program by eliminating the presence within said computing device, at any single time, of a true, accurate and complete copy of said retailed computer program.

14. The method of claim 13 wherein said one-way media comprises cable television cable.

15. A method of protecting demonstrated retailed computer programs from unauthorized duplication comprising the steps of:

transmitting primary data comprising a retailed computer program through one-way media to a computing device in communication with said one-way media and said computing device executing routines in said retailed computer program, at least one of said routines in said retailed computer program requiring additional data to be correctly executed, and

after said computing service has commenced executing at least one of said routines, accessing said primary data carried by said one-way media to obtain said additional data, thereby providing full use of said retailed computer program, whereby unauthorized duplication of said retailed computer program is prevented by the at least one routine within said retailed computer program, in order to be correctly executed, requiring data obtained by accessing additional data carried by said one-way media.

16. A method to protect demonstrated retailed computer programs from unauthorized duplication comprising the steps of:

repetitively transmitting data to a computing device through a one-way media, executing a retailed computer program with said computing device, said computing device being in communication with said media while executing said retailed computer program, said retailed computer program requiring said computing device to communicate with said media to correctly execute said computer program to thereby provide full use of said retailed computer program while said computing device is in communication with said media, and to prevent unauthorized duplication of said retailed computer program by requiring communication with said media during execution of said retailed computer program in order to correctly execute said retailed computer program.

17. Apparatus to provide education coordinated between a student's home and a student's school, comprising:

a computer program having educational content;

a one-way medium of transmission;

a transmitting unit in communication with said medium, said transmitting unit repetitively transmitting said computer program through said medium;

a plurality of computing devices, at least one of said computing devices being located in a school, and at least one of said computing devices being located in a home of a student attending said school,

said plurality of computing devices being in communication with said medium, and each of said computing devices having apparatus to receive transmission from said medium and having apparatus to execute said computer program transmitted through said medium, so that a student may receive education coordinated between the student's home and school by using said transmitted computer program having educational content on the computing device located in the student's home, and again by using said transmitted computer program having educational content on the computing device located in the student's school; and

said apparatus providing full use of said computer program in the student's home and the student's school and said apparatus including means for preventing unauthorized duplication of said computer program.

18. The apparatus of claim 17 wherein said computing devices are located in homes of a plurality of students attending said school.

19. The apparatus of claim 17 wherein at least two of said computing devices are located in said school.

20. The apparatus of claim 17 wherein said one-way medium comprises cable television cable.

21. The apparatus of claim 17 wherein said computing devices are personal computers.

22. The apparatus of claim 17 wherein said computing devices are entertainment computing devices utilizing replaceable read-only memory cartridges that provide game functions.

Description Submit all comments and votes

BACKGROUND

1. Field of the Invention

This invention relates to a system to demonstrate and sell computer software.

2. Description of Prior Art

Today, no methods exist to conveniently demonstrate computer software to the public. Consumers rely on magazine ads, magazine articles, word of mouth, limited demonstration programs, and brief store demonstrations to make their buying decisions. Such information is insufficient for most consumers to judge whether a given computer program will adequately meet their particular needs.

Unlike many other products where features are obvious, computer programs typically have many characteristics which aren't apparent until after many hours of use.

Even where there is certainty that a program will meet a consumer's needs, there can still be uncertainty associated with whether the program will work with a consumer's hardware.

Consumers may also face difficulty finding vendors for particular programs because the number of computer programs available is too large to be stocked locally by most retailers. Customers also encounter uncertainties concerning whether purchased software represents the most up to date versions.

Software authors and publishers have yet other problems associated with software distribution. Because present promotional means are expensive, and inadequately, and in many cases, incompletely represent computer program features, it's very difficult and costly to stimulate product demand, even for very good programs.

Software retailers must deal with yet a different set of problems associated with computer program distribution. Many computer models may be able to run thousands of software titles, each of which may be periodically updated with new versions. This means retailer inventory and spoilage costs are significant.

Several answers to these problems have been proposed. Ogaki et al (U.S. Pat. Nos. 4,674,055, 4,654,799, and 4,672,554) proposed placing vending machines in stores. These units would display video excerpts from software on a screen, but they wouldn't allow program use unless a program were purchased. Without adequate demonstration, or instructions, or the ability for the consumer to try the software on the hardware for which the software is being purchased, Ogaki et al, at best, offered a limited solution. Izumi et al (U.S. Pat. Nos. 4,725,977 and 4,597,058) proposed selling computer programs by having them recorded onto blank or reprogrammable cartridges. Besides having limitations of only working with computers able to access program cartridges, this system provides no instructions on program use, and requires purchase prior to program trial.

Edendorf (U.S. Pat. No. 4,553,252) proposed a program cartridge with means to count uses, thus enabling such cartridges to be rented on a per use basis. Providing rental costs were low and instructions were supplied, this would allow adequate preview of a program before purchasing it, but it would still be inconvenient and limited to cartridge based computers.

The present invention improves on prior art in several ways. It allows trial use of software programs on the hardware which the programs will be eventually used. The present invention permits potential customers trial use of software programs for extended durations ranging from hours to weeks. The present invention offers the most convenient method for purchasing software with both trial use and purchase being conducted within the potential customer's home. The present invention offers a system of retailing software which is significantly lower in cost than competing retail systems.

The present invention offers may other advantages over prior art which readers will find from a consideration of the ensuing description and the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention provides extended trial use of computer programs before purchase on the computer hardware intended to eventually run the programs. The present invention distributes these programs in their entirety, or virtual entirety, for trial, using transmission through cable television lines or open air or the like. It provides potential customers the convenient opportunity to purchase programs from their computer sites directly before or after program trial use.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Definitions

The following glossary is provided for terms unique to the technology of the present invention.

Broadcast stream - signals carrying present invention programming in organized bit stream form.

Broadcast ring - information contained in one repetition of the program broadcast cycle of the present invention.

Receiver/computer - hardware which can identify and retrieve present invention program elements from the broadcast stream.

Computing device - computer portion of receiver/computer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic representation of the present invention's preferred embodiment.

FIG. 2 is a diagrammatic representation of the organization of the broadcast stream employed by the present invention's preferred embodiment.

FIG. 3 is a diagrammatic representation of how the present invention's preferred embodiment organizes information to be broadcast.

FIG. 4 is a digrammatic representation of how information is transmitted, according to the present invention.

DESCRIPTION OF OPERATION

Referring to FIG. 1, the preferred embodiment of the present invention vends computer programs by providing trial use of said programs to potential customers via television cable transmission, and by simultaneously offering means through said cable television transmission for the purchasing said programs for continued use, with said purchase transactions utilizing telephonic communication.

The preferred embodiment has apparatus broadly divided into four parts.

1) The Transmitting Unit #20: stores information to be broadcast including the computer programs to be vended; organizes said information for broadcast; and broadcasts said information.

2) The Transmission Network #202 provides point to multipoint distribution of the information originating from the Transmitting Unit #20.

3) The Computer Sites #34 #57: provide apparatus for trial use of said programs, and have apparatus to place sales orders for said programs.

4) The Authorization Site(s) #212: is (are) the site(s) where sales orders are received and fulfilled.

Referring once again to FIG. 1, a limited set of computer programs and related information is stored in a transmitting unit #20, that is located at a central site. Said information is repeatedly broadcast on a communication network that makes said information accessible to receiving units at multiple sites #34 #35 #57. In the preferred embodiment, said central site is the head end facility of a community cable television system, and said information is broadcast through said community cable television system, in a manner similar to that described in U.S. Pat. No. 3,602,891 [Clark, Molnar, "Continuous Transmission Computer and Multiple Receiver System"]. In said preferred embodiment, the broadcast information of this invention is contained within the signal spectrum of one or a multiplicity of television channels according to the allocation of frequency that is used by the particular community cable system, in such a way that services provided through other channels not used for the purposes of this invention are not disrupted by the signals used for this invention.

In alternative embodiments, other broadcast mediums may be used including open air RF broadcast, fiber optic broadcast etc. Also, other methods of encoding the signals may be used for transmission on a cable system or through other medium. Such encoding methods may distribute the information over a portion of the spectrum that does not correspond to television channel allocations. In some cases, an entire cable distribution network may be used for the purposes of this invention, with no other services such as television broadcasting using the cable network at all.

The set of computer programs that is stored and broadcast according to this invention may include but are not restricted to:

1) programs for trial use and demonstration as inducements to purchase;

2) programs in a form ready for sale for continued use;

3) programs for unlimited free use;

4) programs that perform functions that support the vending system, such as user instruction, order entry, order placement via telephone dial-out, purchase validation, user verification, billing, access control, etc.;

5) programs that provide entertainment, education, information, and other services that will attract users to the vending system;

6) information needed to present graphics, sound, and other communication to users; and

7) coding, security, formatting, and other information incidental to the operation of the vending system.

During operation of the transmitting unit #20, materials to be broadcast, including the set of computer programs to be previewed, are retrieved from broadcast memory #24, which may be partially or entirely volatile or non-volatile; random-access, serial-access, or block-access; static, dynamic, or read-only; semiconductor, magnetic, or other technology; and optionally backed with secondary storage #26 such as hard disk, battery backed RAM, floppy disk, magnetic tape, optical storage, or other devices with or without removable storage media.

In the preferred embodiment, the information that is stored in processor memory #23, broadcast memory #24, and backup storage #26 is loaded and updated remotely using phone lines #32, modems #30, and established phone communications protocols. Other embodiments of the present invention might use satellite feed; or removable media such as floppy disks or magnetic tape or optical media; or other information conveyance means. Various established communication techniques, equipment, and protocols may be used for conveying this information to the transmitting unit #20. Alternatively, all or part of the information may be provided by using read-only memory devices as components of memories #23, #24, or #26 that can be physically replaced to provide updated information.

In the preferred embodiment, loading and updating of information to be broadcast, or of information needed to operate the various functions of transmitting unit #20, are controlled by processing unit #22. This unit may replace the entire contents of broadcast memory #24 with new material, selectively replace portions of the material already stored in broadcast memory #24, selectively delete portions of the material already stored in broadcast memory #24, selectively add new material to the material stored in broadcast memory #24, verify the correctness of material stored in broadcast memory #24, or any combination of the above functions. In the preferred embodiment, within the transmitting unit #20 is a stored program microcomputer that executes instructions from processor memory #23. Processor memory #23 and broadcast memory #24 may be physically distinct units, or may be comprised of a single physical unit used for both purposes. All or part of the memories #23 and #24 may be read-only memory (ROM) or writable memory.

Information is organized within broadcast memory #24 in such a way as to make it rapid and convenient to access for broadcast transmission. In the preferred embodiment, information is organized into blocks that each contain the same fixed amount of information. In other embodiments, blocks of non-uniform size might be used. A portion the information in a block is header in formation #10, which is used to identify the block so that it can be selectively received by receiving unit #38. The header may also contain (but may not limited to) information used to:

1) verify the accuracy with which the block has been received (by means of check sum or cyclic redundancy check or similar techniques);

2) convey encryption information needed to interpret the information in this or other blocks;

3) convey validation information needed to control access to the information in this or other blocks;

4) contain information used by the transmitting unit to identify, schedule, classify, modify, or select blocks as needed to assist the transmitting unit to perform its various functions;

5) satisfy the timing or protocol requirements or both of the transmission network #202, the modulator #201, or the demodulator #207; or

6) select or specify the individual receiving unit or class of receiving unit or user that is enabled to access this or other. blocks.

A second portion of the information in a block is the body #102, which contains the information that is to be loaded into the memory of a receiving unit #38 that has selected said block. Some or all of the information serving the six purposes listed above may alternatively be transmitted in the body rather than in the header of a block or blocks, and information contained in the header may also be loaded into the receiving unit memory.

The amount of information that is contained in the entire block, and in the header and body portions, may be the same for all blocks, or there may be blocks of different sizes, with headers that contain different amounts of information, and with bodies that contain different amounts of information.

Unless otherwise stated, the following section describes a preferred embodiment of the invention. In said preferred embodiment, a block is further divided into multiple lines #111, each capable of containing 188 bits of information. 12 of said lines #111 comprise a block. Each line #111 is transmitted during a single horizontal scan time of a National Television Standards Committee (NTSC) standard signal. The first four bits (tag bits #130) of each line #111 contain information that identifies whether the line is the first line #108 of the twelve lines that comprise a block, or one of eleven continuation lines #109.

The remaining 184 bits of a line are grouped into 23 8-bit bytes #110 of information. The first 20 bytes of the first line #108 comprise the header #101 of the block; the remaining 3 bytes of the first line, along with the 253 bytes of the remaining eleven continuation lines #109 of the block, comprise the body #102 of the block, which thus contains 256 bytes of information.

In said preferred embodiment, the transmission network #202 is a community or an institutional cable television system that broadcasts single- or multiple- channels of such NTSC television signals, normally encoded within a 6 megaHertz frequency band. Cable television systems typically provide many such frequency bands, each allocated to a different television channel or service. It is the intent of the preferred embodiment to encode lines within a signal that is similar to an NTSC signal, so that it can pass through any normal cable television system, including its modulators #28, amplifier #203, taps #204, drops #205, and decoder #206 without interference to other services and without interference from other services or degradation by the transmission network #202 that would produce unreliable operation of the invention.

Techniques for accomplishing these purposes are well-known to the art, and are used for example to encode information in the vertical blanking intervals of video broadcasts. Commonly used techniques exist that retain the blanking, synchronizing, and color burst components of a NTSC signal, and use them to synchronize the modulation and demodulation of serial digital information that is inserted into the portions of the NTSC signal that normally convey video information during a horizontal scan. In the preferred embodiment of the invention, the vertical blanking and synchronizing components of the NTSC signal are omitted, but the horizontal blanking and synchronizing components and the color burst component are retained, and used to synchronize the demodulator #207 so that it can reconstruct the 188 bits that comprise each transmitted video line #112. All horizontal scan intervals, or a portion of them, may be used for the transmission of lines.

A preferred means for encoding digital information makes use of a horizontal synchronizing pulse and color burst similar to those used in an NTSC television signal to determine the timing of the encoding and decoding of a bit-serial form of the digital information within the portion of an NTSC horizontal line that is usually used to contain video information. The horizontal synchronizing pulse defines the beginning of a line; the color burst defines the timing of individual bits within the video portion of a line.

The duration of a single horizontal scan line is equal to 227.5 cycles of the color burst frequency of 3,579,545 cycles per second. In the preferred embodiment, the important events during a consecutive pair of horizontal scan lines all occur at times that are referred to the color burst phase. The color burst is a group of 9 cycles of sinusoidal signal at the color burst frequency that is transmitted in a specified time interval following the end of a horizontal synchronization pulse. The time of important events in the signal is conveniently indicated by giving the number of color burst cycles since the time of the leading edge of the horizontal synchronizing pulse If the signal uses the interlacing structure that is defined in the NTSC standard, the timing relationships are slightly difference in a given line and the following line, so it is necessary to define the signal timing for an interval that includes two consecutive lines. This pattern is repeated by successive pairs of lines. The first line of such a pair is called "even", the next is called "odd".

The following table defines the times of critical events relative to the leading edge of the horizontal synchronizing pulse for an even line:

______________________________________ FIG. 4 ref. # Cycle Event ______________________________________ 202 0.0 Horizontal synchronizing pulse leading edge 204 16.5 Horizontal synchronizing pulse trailing edge 206 19.0 Color burst begins (even line) 208 28.0 Color burst ends (even line) 210 34.0 Digital signal begins (even line) 212 222.0 Digital signal ends (even line) 214 227.5 Horizontal synchronizing pulse leading edge 216 244.0 Horizontal synchronizing pulse trailing edge 218 246.5 Color burst begins (odd line) 220 255.5 Color burst ends (odd line) 222 262.0 Digital signal begins (odd line) 200 450.0 Digital signal ends (odd line) 202 455.0 End of line pair (0.0 of next pair) ______________________________________

The digital signal is encoded serially during the interval from 34.5 to 222.5 cycles, and from 262.0 cycles to 450.0 cycles, by selecting one signal level for a "0" and a different signal level for a "1". The length of the interval available for digital encoding during each horizontal line video interval is 188.0 cycles of the color burst frequency. One bit is encoded during each cycle. It is convenient to choose the level that would normally indicate "black" in video transmission to encode a "1", and the level that would indicate "white" to encode a "0".

The 188 bits encoded in a horizontal line comprise 23 bytes of 8 bits each, plus four additional bits. The 23 bytes convey the information that is to be communicated to the receiving apparatus; the additional four bits are transmitted at the beginning of a line and are used to distinguish the first line of a block from continuation lines, and may optionally be used to distinguish normal blocks that carry information to be loaded into the receiver from special blocks, such as blocks used to convey information used for decryption, error correction, or other special purposes.

In the preferred embodiment, the signal just described is generated at signal levels that correspond to standard practice for NTSC video signals, and is used as the video input to a standard television channel modulator. This modulator generates an output signal in a six megaHertz frequency band allocated for this service. The rise and fall times and frequency spectrum of this synthesized video signal are controlled by filtering or other means so that the vestigial-sideband amplitude-modulated signal that is produced by the modulator is compatible with normal video signals that may be transmitted on frequency bands allocated to other services in the same cable.

In other embodiments, the invention may use portions of the cable spectrum that are narrower or wider than the 6 megaHertz band of a typical television signal. It may also use techniques other than frequency-division multiplexing in order to permit sharing of the transmission system with other services, such as time-division multiplexing of digital signals with the signals of other services. Different effective bit transmission rates may be used, with a variety of modulation and encoding techniques. This invention requires only that the network can communicate signals of adequate transmission rate in one direction, from the transmitting unit #20 to one or more receiving units #38, and does not depend in any way upon the ability that some cable television systems may have for conveying signals in the opposite direction.

Returning to the description of the preferred embodiment, the sequencing of blocks and lines in the broadcast stream is as follows. The first line #108 of a block #100 contains a block number #120 that identifies that block. The lines that comprise a particular block are not transmitted during consecutive horizontal scan intervals, but rather some number of scan intervals separate the transmission of the successive lines of a block. In the preferred embodiment, each successive line of a block is transmitted N horizontal scan intervals following the preceding line of that block. N may be fixed number for all blocks, as it is in the preferred embodiment, or it may have different values for different blocks.

The purpose of having an interval separating the lines that comprise a block is that this allows time for the receiving apparatus to examine the block number and other information that is contained in a line, and to make decisions and execute procedures that are needed to process the line that was just received or prepare for the reception of the next line of the block. In particular, in the preferred embodiment, a value of N=19 allows sufficient time that these operations can be performed by programs operating in the computer #42 or video game system 45 (such as typified by the Nintendo NES) both hereinafter interchangeably referred to as "the computer #42 that is part of the receiving unit #38, making it unnecessary for the receiver interface unit to perform these operations.

There is a particular advantage in choosing N so that it is relatively prime with respect to the number of lines M in a block. This allows an efficient interleaving of lines that allows all of the following requirements to be satisfied:

1) The lines comprising every block are spaced at uniform intervals of N horizontal scans;

2) The first line #108 of successive blocks can be spaced at uniform intervals of M horizontal scans;

3) The lines that comprise a sequence of any number of blocks can be transmitted in a way that makes use of every horizontal scan, once the first N blocks have been transmitted;

4) If blocks are transmitted in such an order that their block numbers #120 are in ascending order, the sequence of first lines #108 of these blocks will contain the block numbers in the same ascending order; and

5) There is a time interval of (M-1) horizontal scans separating the transmission of the first lines #108 of any consecutive blocks.

In the preferred embodiment, the receiving apparatus makes use of conventional means for selecting the frequency band used for transmitting the digital broadcast signal, and demodulating the signal into a composite video signal that reproduces the video signal that was provided to the modulator that generated the transmitted signal. The receiving apparatus may use conventional techniques common in television receivers, such as automatic gain control, automatic frequency control, surface acoustic wave intermedicate frequency filters, and synchronous demodulation, to improve the fidelity with which the original video signal is reproduced. It may use manual or electronic control to select the frequency band to be received, so that multiple bands carrying a digital broadcast signal may be received. This selection may optionally be under the control of the computer #42, or may be made manually. The same apparatus may also be optionally used to receive video signals for other purposes, such as television viewing, in order to share the cost of the apparatus over multiple uses. The horizontal synchronizing signal and color burst signal are separated from the demodulated video signal by conventional means. The color burst signal is used to phase- and frequency-lock a local crystal oscillator that operates at the color burst frequency of 3,579,545 cycles per second, using means that are conventionally used for the reception and decoding of NTSC color video broadcasts. This local color oscillator signal, and the horizontal synchronizing pulse, are used to determine the instants at which the composite video signal is sampled to recover the serial binary data that are encoded in it. One sample is taken for each cycle of the local color oscillator.

This recovered serial digital signal is input to a conventional shift register circuit, whose contents are shifted once in every color clock cycle and assembled into 8-bit bytes or other convenient groupings. This information is then provided to the receiver interface unit for further processing and interpretation.

The receiver interface unit #38 is equipped to identify a video line #112, and determine whether it is a first line #108 or a continuation line #109, and if it is a line of the specific type desired, to receive and store the 23 bytes of information that it contains. The receiver interface unit #38 is controlled by the computer #42, which specifies to the receiver interface unit #38 the next type of line that it should detect and store. When such a line has been detected and stored, the receiver interface unit #38 signals the computer #42, by means of a signal flag, program interrupt, DMA transfer, or similar means, that a line is ready. The computer #42 then accesses the bytes that are stored in the receiver interface unit #38, by means such as address-mapped I/O, and carries out whatever procedures are necessary to identify the information that has been received, and, if required, transfer it to storage locations in the memory, processor, or peripheral devices of the computer #42.

A representative procedure that is used for searching and loading a specific block follows:

The computer #42 directs the receiver interface unit #38 to identify and store the next first #108 line. The receiver interface unit detects the next video line that contains the proper code in its tag bits #130, and stores the information contained in that line. In then signals the computer #42, which compares the block number that has just been stored with the number of the desired block. If they do not agree, the computer repeats the same direction to the receiver interface unit, which can be done in sufficient time that the very next first line can be identified and stored by the receiver interface unit.

If the block numbers agree, no such repeated direction is given to the receiver interface unit, and it begins to count successive horizontal scans and prepares itself to read the Nth following line, which should be a continuation #109 line. While this is taking place in the receiver interfac