NETDATA
| Company type | File format |
|---|---|
| Industry | Computing, Data transfer |
| Products | Data transfer and storage format for IBM mainframes |
NETDATA is a file format mainly utilized for transferring and storing data on IBM mainframe environments, though versions exist for other platforms as well.
Description
NETDATA files are composed of 80-byte card image records that hold unloaded file content along with metadata necessary for reconstructing the original file on the destination system. A typical NETDATA file begins with multiple control records, followed by data records, and concludes with a trailer record. Each record shares a consistent structure:
- A one-byte length field specifying the logical segment size, which can be up to 255 bytes; segments may contain as many as 253 bytes of actual data.
- A one-byte flags field denoting segment properties:
- X'80' - marks the first segment within a record
- X'40' - indicates the last segment of a record; single-segment records use X'C0'
- X'20' - identifies the segment as part of a control record
- X'10' - shows that the segment carries the next record number
- X'0F' - reserved for future use
Control records
Control records include a six-character EBCDIC identifier located in bytes 2 through 7 and contain self-describing fields known as text units. Each text unit consists of a key, length, and associated data. Systems disregard any text units that are not relevant.
Header Control Record
The initial record in a NETDATA file, labeled "INMR01", conveys sender details such as node, timestamp, and user ID. It also specifies control record segment length, target node and user ID, and may optionally request an acknowledgment of receipt, define the data format version, state the number of files being sent, and include a user parameter string. While CMS supports transmitting only one file per session, other systems might permit multiple files.
File Utility Control Record
Known as "INMR02", this record provides instructions for file reconstruction. It identifies the file number in cases of multiple-file transmissions and describes file attributes including organization (INMDSORG), record length (INMLRECL), record format (INMRECFM), estimated size (IBMSIZE), and any utility program(s) (INMUTILN) required for rebuilding. Additional optional metadata can specify block size, creation date, directory block count, dataset name, expiration date, mode number, last modification or reference dates, member names for partitioned datasets, note files, and user parameters.
Data Control Record
Preceding the data records, "INMR03" outlines data characteristics similarly to the Utility Control Record. It details organization (INMDSORG), record length (INMLRECL), format (INMRECFM), and size (IBMSIZE). This record is ignored by CMS but utilized by TSO/E systems.
User Control Record
Designated "INMR04", this optional record may appear at any point within the stream. While CMS disregards it, other systems employ it to carry a User Parameter String (INMUSERP).
Trailer Control Record
Signifying the conclusion of the file, "INMR06" contains no further data.
Acknowledgement Control Record
Employed by recipients to confirm receipt of transmission, "INMR07" includes File Name (INMDSNM) or Note File (INMTERM) text units and may optionally feature an Origin Time Stamp (INMFTIME).
Note files ("PROFS notes") function as brief messages similar to letters.
Data records
Following the Data Control Record (when available) and preceding the Trailer Control Record, data records are marked by their flag value. These records may reach a maximum size defined by INMLRECL and are sent in several segments, each up to 253 bytes. For transmission purposes, these segments are divided into 80-byte records, which the receiver then reconstructs. The flag values specify whether a file record is beginning, ending, or complete. The bytes within these records can include any bit configuration without restrictions on specific character values.