JPH0222732A - Data compressing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] This data compression device relates to a data compression device that compresses or uncompresses data, and when the amount of data increases, the data compression device prevents the increase in the amount of data by writing the true data as is. A data compression means for compressing data from a host CPU, a first holding means for holding compressed data, and a first holding means for holding compressed data;
a second holding means for holding data from the host C;
A first counting means for counting the number of bytes of data from the PU, a second counting means for counting the number of bytes of compressed data, and a comparison means for comparing the output of the first counting means and the output of the second counting means. and instruction means for instructing the data compression means to compress or non-compress data based on the comparison result of the comparison means.

[Industrial Application Field] The present invention relates to a data compression device that compresses or decompresses data.

Generally, data compression is a method for apparently increasing the storage capacity of an external storage device.

The idea behind this data compression is that, as shown in Figure 3, when data is received from the host CPU via a channel and the data is written to the storage medium, the data compression mechanism (
1) run-length compression, which converts consecutively occurring characters into "character code" x n bytes of data, and (2) coded compression, which converts frequently occurring characters into abbreviated codes, to reduce the amount of data and save space on storage media. This increases the apparent storage capacity.

For example, when the true data from the host CPU is "C2C3C5C5C5C5D1", run-length compression converts the 5-byte "C5" code to 3-byte "C5F D O5".
” and compresses it into data of '02C5FDO5D1'.

Furthermore, as shown in Fig. 4, encoding compression converts characters that appear frequently among the characters of originally 8-bit information, such as "space" to 3 bits, 'A' to 4 bits, and "E P
I'D 11 Compress "'M" to 5 bits.

On the other hand, characters that appear very infrequently, such as "Z II," are increased to 13 bits (see FIG. 5).

In this case, it is necessary to take into account the actual data compression effect and prevent data m from increasing.

[Prior Art] As a conventional magnetic tape control device having a data compression mechanism, there is one shown in FIG. 6, for example.

In FIG. 6, data from host CPtJ1 is input to data compression mechanism 5 through channel 2, channel interface 4 in magnetic tape control bag @3, and run-length compression and/or coded compression is performed in data compression mechanism 5. The compressed data is stored in the data buffer 6. The compressed data is then written onto the magnetic tape 8 by the read/write control mechanism 7.

The compressed data written on the magnetic tape 8 is stored in the data buffer 16 by the read/write 1 to the control mechanism 7, and then restored to true data by the data restoration mechanism 9 and sent via the channel interface 4 and channel 2. Hoss 1~
It is read out by CPU1.

[Problem to be solved by the invention] However, in such conventional magnetic tape control devices, when compressing data, there is an incompatibility between the compression algorithm and the nature of the data, which causes the compression effect to be ineffective. teeth,
When looking at one piece of data, it does not change dynamically,
Rather, it is seen as a data characteristic that appears throughout the data and is expected to persist until the end of the data.

Therefore, when data compression is performed unilaterally, there is a problem in that the amount of data increases due to the incompatibility between the compression algorithm and the nature of the data.

The present invention has been made in view of such conventional problems, and is a data system that prevents an increase in the amount of data by inserting the true data as is when the amount of data increases. The purpose is to provide a compression device.

[Means to solve the problem] FIG. 1 is a basic configuration diagram of the present invention.

In FIG. 1, 18 is a data compression means for compressing data from the host CPU 11, 22 is a first holding means for holding compressed data, 17 is a first counting means for counting the number of bytes of data from the host CPU 11, and 23 14A is a comparison means for comparing the output of the first counting means 17 with the output of the second counting means 23. 14B is the comparison result of the comparison means 14A. This is an instruction means for instructing the data compression means 1B to compress or uncompress data.

U Effect J In the present invention, the actual number of bytes of data is compared with the number of bytes after compression, the actual compression effect is checked, and the data compression means is instructed to compress or non-compress. and,
When the number of bytes of true data is greater than the number of bytes of compressed data, compressed data is written; otherwise, true data is written.

Therefore, when the data m increases due to incompatibility between the compression algorithm and the nature of the data, it is possible to prevent the data amount from increasing by writing the true data from the second holding means onto the magnetic tape.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention.

First, to explain the configuration, in FIG. 2, 11 is a host CPU, 12 is a channel, and 13 is a channel interface data transfer control section (hereinafter referred to as data transfer control section). The data transfer control unit 13 controls data transfer with the host CPU 11 via the channel 12.

The data transfer control unit 13 is a microprocessor (hereinafter referred to as M
When receiving an instruction to start data transfer from the PU (PU) 14 via the signal line 15, the data is received from the host CPU 11 via the channel 12 and transferred via the bus 16 to the channel byte counter (first counting means) 17; It is sent to the data compression mechanism (data compression means) 18 and the second data buffer (second holding means) 24.

Further, when the data transfer is completed, the data transfer control unit 13 instructs the MPU 1 to terminate the data transfer via the signal line 19.
Notify 4.

The channel byte counter 17 counts the number of bytes of data (true data) sent from the data transfer control section 13 and outputs the number of bytes of true data to the MPU 14.

The data compression mechanism 18 receives a data compression or non-compression instruction from the MPU 14 via the signal line 21, compresses the data by run-length compression and/or coded compression according to the compression instruction, and transfers the compressed data to the first data buffer ( first holding means) 22 and device byte counter (
(second counting means) 23.

Further, true data is stored in a second buffer (second holding means) 24 via the bus 16.

Compressed data stored in the first data buffer 22 or uncompressed data stored in the second buffer 24 is written to a magnetic tape (not shown) by a read/write control mechanism (not shown).

The device byte counter 23 counts the number of compressed data output from the data compression mechanism 18 and outputs the number of bytes to the MPU 14.

When the MPU 14 receives the data transfer end notification from the data transfer control unit 13, the MPU 14 sets the channel by 1 to counter 17.
The number of bytes of true data from the device byte counter 23 is compared with the number of bytes of compressed data from the device byte counter 23 to check the compression effect.

When the number of bytes in the channel byte counter 17≦the number of bytes in the device byte counter 23, the MPU 14 instructs the data compression mechanism 18 to compress the data, and when the number of bytes in the channel byte counter 170>the number of bytes in the device byte counter 230, the MPU 14 instructs the data compression mechanism 18 to compress the data. The compression mechanism 18 is instructed not to compress, and the true data is stored in the second buffer 24.

Therefore, the MPU 14 uses the channel byte counter 17
It has the functions of a comparison means 14A that compares the output of the device byte counter 23 with the output of the device byte counter 23, and an instruction means 14B that instructs the data compression mechanism 18 to compress or not compress based on the comparison result.

Next, the operation will be explained.

First, upon receiving an instruction to start data transfer from the MPU 14, the data transfer control unit 13 receives data from the host CPU 11 via the channel 12 and sends the data to the data compression mechanism 1.
8. Channel by l-counter 17 sends data to second data buffer 24, and when data transfer is completed, M
The PU 14 is notified of this.

The data compression mechanism 18 performs run-length compression and/or code compression on data according to a compression instruction from the MPU 14 and sends the compressed data to the first data bag 722 and the device byte counter 23 .

On the other hand, when the MPU 14 receives the data transfer end notification from the data transfer control unit 13, the MPU 14 starts the channel byte counter 1.
Compare the number of bytes of true data from device byte counter 23 with the number of bytes of compressed data from device byte counter 23, and if the number of bytes of channel byte counter 17 is equal to the number of bytes of device byte counter 23, the data compression mechanism 18 The real data is stored in the second data buffer 22 by instructing non-compression of the data.

On the other hand, when the number of bytes in channel byte counter 17>the number of bytes in device bye 1 to counter 23, MPU1
4 instructs the data compression mechanism 18 to compress and stores the compressed data in the first data buffer 22.

Therefore, if the amount of data increases due to incompatibility between the compression algorithm and the nature of the data, it is possible to prevent the amount of data from increasing by writing the true data from the second data buffer 24 to the magnetic tape.

Note that when the number of bytes in the channel byte counter 17≧the number of bytes in the device byte counter 23, the amount of data can be reduced by performing data compression.

[Effects of the Invention] As explained above, according to the present invention, the actual compression effect is checked by comparing the true number of data bytes and the number of compressed data bytes, so the amount of data increases. In this case, the true data can be written as is, and it is possible to prevent data from increasing.

[Brief explanation of the drawing]

Figure 1 is a basic configuration diagram of the present invention, Figure 2 is a block diagram showing an embodiment of the present invention, Figure 3 is an explanatory diagram explaining the concept of data compression, and Figure 4 is the concept of coding compression. FIG. 5 is a graph explaining the concept of coding compression, and FIG. 6 is a 10-point diagram showing a conventional example. In the figure, 11: host CPU, 12: channel, 13: data transfer control unit, 14. 14A, 14B: microprocessor (comparison means, instruction means), 15: signal line, 16: bus, 17: channel by 1~ Counter (first counting means), 1
8: Data compression mechanism (data compression means), 19.21:
Signal line, 22: first data buffer (first holding means), 23: device byte counter (second counting means), 24: second data buffer (second holding means). Tea-evening fL? -n/14 N2ε Fortune-telling 90th month 11W Figure 3 Space 3 bits 4 bits 13 hits 1 Code 5Nk/1fii way L a Donkey 1 U5 Victory month Figure 4 Coding power How to Serve King Wa 1 & How to Serve It Graph 5th Figure 170 Book 170 Figure 6

Claims (1)

[Claims] A data compression means (18) for compressing data from the host CPU (11), a first holding means (22) for holding compressed data, and a second holding means (24) for holding data from the host CPU (11). ) and a first counting means (17) for counting the number of bytes of data from the host CPU (11).
and a second counting means (2) for counting the number of bytes of compressed data.
3), a comparing means (14A) for comparing the output of the first counting means (17) and the output of the second counting means (23), and compressing or non-compressing data based on the comparison result of the comparing means (14A). A data compression device comprising: instruction means (14B) for instructing the data compression means (18) to perform compression.