DE1424388A1 - Procedure for checking magnetic tapes - Google Patents

Description

Pafenfcmwalf

to Wilhelm MgM ■ ' _{4 / o / OQC}

FiankfurfyMain-1 1424388

Parkslrasse 13

P 14 24 388. O July 11, 1968

General Electric Company Re / Li / Schl-2703

Procedure for the test reading of magnetic tapes

The invention relates to a method for test reading with two remotely located magnetic heads for correctness of Data stored in blocks in several tracks of a magnetic tape, including row and column parity data » with markings indicating the beginning and end of the block.

The pace of operation of data processing systems with input and output devices is generally uneconomical, because today the data processors work much faster than the peripheral devices. Therefore, the magnetic tape is often called Aids used to provide high-speed interim and rapid data input and output to and from the data processor Provide auxiliary storage.

The data is generally on a magnetic tape in one another separate blocks or words that are a certain distance apart. To record To synchronize data on the tape and the reading of data from the tape must be in the selected tape track in certain Markings may be provided which indicate the beginning and the end of a block.

To ensure that the recorded on the magnetic tape If data are correct, it must be possible for a device to check the correctness of this data indicator. Palis at If errors are observed during such a check, aids should display the incorrect data. If data is on recorded on the tape as planned, any

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61 para. 2 no. T SLu 3 Ses Ana

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Tools check whether this data has actually been recorded in the desired manner.

The invention is therefore based on the object of providing a method " for testing magnetic tapes, with the aim of checking whether information made available for writing has also been correctly inscribed on the tape.

Such processes are already known. For example In a known device, a double head is used, which is designed so that the read and the write gap are arranged very close to each other, while at the same time the risk of crosstalk due to the use of additional Auxiliary gaps and reduced by the special coil arrangement

will. These auxiliary columns ensure the greatest possible de-_

coupling »The shear caused by the additional auxiliary gaps must be viewed as a disadvantage in this construction, which is the linearity range for linear recordings expand ', but with pulsed (digital) recordings Increase the required electricity demand (German Auslegeschrift 1 072 830).

In another known device, a data block corresponding, for example, to the length of a print line " can, when the tape is stationary, by the advance of the write head enrolled. The head then scans the written data block again to remove the written Information with the information to be registered to compare. If this comparison turns out positive, the tape is moved on by one block length. It will Band area corresponding to a data block by sensing brought into the correct position in relation to the writing head by optical markings. (German exposition 1 091 370).

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However, this well-known institution deals exclusively with the input control of slowly working outside Additional devices such as typewriters. The task is there in doing so, promptly checking each individual data block after entering it, but still checking the bit density on the To make the band as large as possible. Should, however, the data made available in a buffer store be overwritten on the tape this procedure is not applicable because it is necessary because of the ongoing head movement and the subsequent gradual belt movement is far too slow.

According to the invention, the object is now achieved in a method of the type described above by the following method steps: storage of a third marking all block start marks before the data is written in a manner known per se with the aid of a write head j Triggering data entry into the tape upon scanning of the third mark; Storage of a parameter for the Data in an off-tape location; Triggering the reading of the data just stored on the tape, as is known per se, when scanning the block start marking; Derivation of a synchronization signal when the block start marker is scanned following the scanning of the third Mark; and comparing the data thus read from the tape with that coming from the synchronization signal Command out with the corresponding original data that have been stored in the separate memory location to ensure the correctness of data immediately after being written to check 'and to indicate a blank or faulty tape.

This procedure has the following advantages:

1. The write head and the control read head can be arranged so far from one another that the difficulty of crosstalk can be controlled.

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2. The time delay between the registered letter and the control-reading no longer plays a role for the test, because the necessary synchronization signals are available.

3. The control read head is only just before the start of a data block switched on. So it does not scan the spaces on the belt between two blocks, so that the noise as well as errors on the tape in these spaces do not result in incorrect checks. It is remembered that limiter amplifiers are usually placed after the heads, so it is often not easy to switch between distinguish between the noise and one bit.

4. The control readings can be carried out continuously and at the usual tape reading speed. So it is without It is also possible to include data that the arithmetic unit has made available in a buffer for tape storage at to control the storage from this buffer.

The invention is explained in more detail with reference to figures.

Fig. 1 is a schematic representation of devices which record data on and from magnetic tape read this.

Figure 2 is an illustration of the tape from the write head impressed magnetic flux direction; the brackets enclose a data word, with those attached to the dashed Numbers arranged in lines indicate the positions of the data word.

According to FIGS. 1 and 2, data are stored on a magnetic tape 6k0 in groups or blocks 6k1 . A data block contains, for example, 100 data words, each consisting of eight volume digits or volume positions. Each volume number contains

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five bits, four of which are the system code for one to be processed Form digit. The fifth bit is a column parity bit for the volume number. Seven of the eight volume digits of a data word contain the seven digits of the system to be processed Data word including the seven associated column parity bits. The eighth volume digit contains five line parity bits for the relevant data word.

The data are stored on the magnetic tape in ten parallel tracks 1 to 10, which run in the longitudinal direction of the tape. Ten bits are therefore stored in ten parallel tape tracks on an imaginary line perpendicular to the longitudinal direction of the tape. This line is called the vertical recording point. The four data bits of a tape number are stored in tracks 1 to h and the associated column parity bit is each stored in track 5. The four data bits of a further digit are stored in tracks 6 to 9 and the corresponding column parity bit in track 10. Therefore, two volume numbers are stored next to one another in a vertical recording position.

A complete data word appears on the tape in four adjacent vertical recording locations stored; a data block with 100 words therefore contains 400 recording positions. As can be seen in Figure 2, the line parity digits are and the sixth, fourth and second volume number of the data word 'in tracks 1 to 5 and the seventh, fifth, third and first volume number stored in tracks 6 to 10. The distance between adjacent vertical recording points and the speed of the tape are set so that that a recording location is recorded or read about once during a predetermined period of time. Therefore the reading or recording of the complete data word takes place in about four such periods of time.

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A plurality of write heads 642 arranged opposite a track record the data on the magnetic tape in the corresponding one Track on. During the writing process, for example, a current is uninterrupted through the write head in a Direction sent through so that the track assigned to the head magnetizes parallel to the longitudinal direction of the tape and becomes saturated. The direction of current for the write head depends on the data to be written. Just the O bits are marked on the magnetic tape. An O-bit draws is characterized by a reversal of direction in the saturation of a track. Every time a write head should record a 0, the current in the winding is reversed. A 1-bit will be represented by the lack of a change in direction of the magnetic flux in a recording location.

Several read heads 643 arranged opposite one track each can scan the magnetic flux recorded in the assigned track and one each time an O bit is scanned Deliver output pulse. With a 1-bit, no output signal is emitted by the assigned read head.

The individual data bits and the type of storage on the tape are indicated in FIG. The arrows indicate the saturation magnetic flux direction of a track. In the vertical recording position for the fourth tape number, the first, third and fourth tracks have a reversal of the saturation direction, while the second and fifth tracks have an unchanged saturation direction. Consequently, the Spaltenparitätbit for the fourth digit is a 1, and Cn, four bits of data in the tracks 4 to 1 loud 0010. The JH ₄ following table illustrates the angege in Fig 2 - bene data word ^ f:.

_o Data digits on the magnetic tape (Fig. 2)

Row parity - 7th 6th 5th 4th 3rd 2nd 1st digit -

0 1 1 0 T 0 0 1

1 0 1 0

0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 1 1 0 0 0 0 1 0 1 0 1

The bits below the second horizontal line and to the right of the vertical line are data bits. The top line contains the split parity bits for the assigned digits. The column parity bit is a 1 when there are an odd number of data bits. The bits in the second through fifth rows of the left column are row parity bits for the assigned rows. The row parity bit is a 1 if there are an even number of bits in the row in question. The bit in the first row of the left column is the column parity bit for that column. No line parity bit is provided for the first line. ' ύ

A block marker track 11 shown in Fig. 1 contains markings which indicate to the write buffer stage of the system an area on the magnetic tape into which a data block is to be written and which indicate to the read buffer stage of the system the location of the data block. Three block markings, namely an oC block mark 51, a / j block mark 52 and a JjT block mark 53 are used. The different block markings can contain different numbers of O-bits. An analyzer 6kk (FIG. 2) for determining the block markings picks up signals from a reading head 6k3 'which examines the magnetic field of the block marking track. Corresponding to the received signals, the analyzer 6kk supplies a plurality of output signals which indicate the corresponding block markings.

When data are to be read, the scanned / S block mark 52 triggers this process and the analyzer 6kh delivers a signal 61. When the J * block mark 53 is scanned, the analyzer 6kk delivers a signal 62 indicating the reading process · completed should be written $ 1 data after scanning the OC -Markierung Venn, the analyzer gives a signal 63; if then the β mark

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is scanned, the analyzer delivers the signal 61, which acts as a synchronizing signal in this mode of operation. This signal synchronizes the recording, reading and error checking of the data. If the J ** signal 53 is sampled, the analyzer outputs signals 64 and 62, which record and read the system, respectively break up.

The OC and (S signals are used to indicate the beginning of a block for the relevant recording or reading. The ^ mark is used to indicate the end of the ϋ

Blocks to finish reading or writing.

According to FIG. 1 s, the track 11 indicates the starting point (OC) 51 of the write-in, the starting point ( / $ ) 52 <8s of reading and the end point (J "") 53 for a block. These markings are expediently recorded beforehand on the tape using a device _9, for example, tape editor, before the tape is used in the system, or can one? Seforeibkepf can be used if a previously edited volume is available. Start-up distance of the tape determines the distance between the & C marking 51 and the i ^v marking 53 of the preceding block. The β mark 52 follows the OC mark 5 * in. A distance that is less than the distance between the. Mind is. All data of a given block is recorded between the ß- ΐ3η & Α ~ mark .

When writing, the "X" mark 51 indicates that the tape has reached operating speed (this is the case when the character cc is scanned by the reading head) and that the writing heads © are at the beginning of the block. The β -Sysabol 52 outputs aa _s when the gap of the read heads approaches the beginning of the block. The Y ^ symbol 53 indicates the end of the block and indicates the execution of the command.

BAD ORiGINAL

8G9802 / 0287

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The reading heads are hidden in the gaps between the blocks, that is between the / "marking 53 and the subsequent β marking 52. This deactivation is necessary so that magnetic flux discontinuities in the gaps are not read as real data or noise is generated.

The alternate font is used for recording, in which only one of the two binary digits is represented by a one-time change between two magnetization states. In the present case, a binary O-bit is indicated by a reversal of the flow direction and a binary 1-bit by a lack of flow change. Between two recorded O bits is saturated Λ the band in both directions. During reading, the O-bits are displayed as voltage pulses, the amplitudes of which are proportional to the time derivative of the change in flux at the read head gap when the head runs along the tape at a constant speed. A sampled change in flux or the resulting pulse provides the information that an O-bit is present. No change means either a 1-bit or the absence of any information.

The data to be written on the magnetic tape is transferred from the Computing machine memory in the write buffer stage (or a Memory) where the format and parity requirements are met. The data then becomes a tape control unit ™ that is, in turn, a selected tape processing device actuated.

1, the read head 643 is attached close to the write head 642, so that it can deliver an echo of the written data approximately at the same time as the data is written, whereby it can be checked whether the recorded data correspond to the data that were fed to the write head . This test contains logic that allows the implementation of an echo parity check on the data that are being recorded on tape dee. The logic is contained in an echo checking arrangement which issues a warning signal if a parity error occurs. 8AD

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-TG-

To show zts how the test facility works when z. B. the write signal 51 is received, followed by the ο signal 52, an echo synchronization flip-flop is set, which enables the system to read an echo. During recording, the data being written is scanned when the tape is under

runs along the read head arranged next to the write head, and checked. This error display system does not necessarily compare the recorded data with the original data, but can instead read the data to check the parity. This echo reading arrangement must take advantage of the fit mark 52 in order for the echo reading to be performed by a reading gate circuit; both column and row parity can be checked in this way.

In particular, all ten write heads 6kZ can each be connected to a corresponding separate read head. When the data is presented to the write heads for recording, the row and column parity data set flip-flops associated with the read heads. If the synchronizing signal is generated by the presence of OC-mark 5 ^ and the A-mark 52, the read heads read the row parity data from _$ follow the data just written. When the data matches the line and parity data originally presented to the write head, the flip-flops return to their original state. If an error occurs ₈ , one or more flip-flops will not return to their original state when the read heads scan the data that has just been written.

When the Δ mark 52 of the moving belt is scanned, an associated read synchronization flip-flop is switched to its set state so that data can be received from the read head is shown) connected in its unstable state takes place so that the delayed standstill "the Erezeuguing © crystalline block end instruction is. characterized delayed until the multivibrator in its stable state switched back *

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An error warning device is actuated at the end of a block when a blank tape has been inserted into the tape transport or when a visual pickup process has been carried out without the echo data occurring. A blank tape flip-flop (not shown) can be brought out of its original state when a write command is supplied to the write heads by the system. The flip-flop is then switched back to its original state by the detection or display of written data by a read head. If this «flip-flop is not in its original state after the detection of a je» mark 53 (Fig. 1), the alarm device is triggered to indicate that the A tape is empty or that the data to be recorded did not provide any echo test signals

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Claims (5)

Patents 1 . Procedure for test reading with two spatially removed lying magnetic heads for correctness of several Tracks of a magnetic tape data stored in blocks, including row and column parity data, with markings indicating the beginning and end of the block, marked by the following process steps! Storage of a third mark before all Rlockaafangsmarkieriangen before writing the data in a known manner with the help of a write head; Triggering UBT data entry into the tape upon scanning the third mark; Storage of a parameter of the data to be written in a memory location separate from the tape; Triggering the reading of the data just stored on the tape, as is known per se, when the block start marking is scanned; Deriving a synchronization signal when scanning the block start marking following the scanning of the third marking; and comparing the data thus read from the tape in response to a command from the synchronization signal with the corresponding original data stored in the separate memory location to check the correctness of data immediately after writing and to indicate a blank or defective tape . 2. Ancestor-according to claim 1, using a Control system that drives a data processing device is assigned and contains read and write heads arranged next to one another, marked thereby net, since ·· the write heads only then transfer data to the tape write when the system has scanned the third mark and that the read head reads data from the tape when the SyeteM the marking indicating the beginning of the block has sampled. Method according to claim 2, characterized in that that the writing of the third mark and the writing of the mark indicating the beginning of a block Markings follow one another in such a way that these markings on the tape are at a distance from one another that is smaller as the distance between the read and write heads measured in the longitudinal direction of the tape - is. 4. Method according to one of claims 1 to 3 »characterized in that the stored separately from the tape characteristic quantities row and column parities are that the information similar to a command from the synchro is read out nisiersignal, those row and column parity data that have just been written to the tape, and that the comparison compares the stored parity data with the parity data that has just been read. 5. The method according to any one of claims 2 to k with simultaneous use of a device for detecting empty tapes and a device for generating a warning signal, characterized in that a bistable switching device is switched to the one state when detecting a writing mark by the control system and when detecting written data is switched to the other state, and that a warning signal is emitted if the signal indicating the end of a block is detected and the bistable switching device is still in the first state. BAD ORiQJNAL 809802/0267