MVS Header Record for the ERDS

Table 1 shows an example of the MVS header record for the ERDS.

Table 1. MVS ERDS Header Record
Offset Dec(Hex)	Size(bytes) Alignment(bits)	Field Name	Description
0(0)	2	CLASRC	Header-record identifier. Each bit in this field is set to 1 unless critical data has been destroyed.
2(2)	4	LOWLIMIT	Address of low extent. Track address (in CCHH format) of first extent of SYS1.LOGREC.
6(6)	4	UPLIMIT	Address of high extent. Track address (in CCHH format) of last extent of SYS1.LOGREC.
10(A)	1	MSGCNT	Count of the number of times LOGREC-full message has been issued (maximum is 15).
11(B)	7	RESTART	Address of record entry area, and address of time-stamp record. Starting track address (in BBCCHHR format) of the recording area on SYS1.LOGREC. If a time-stamp record is present, it begins at the address pointed to by this field.
18(12)	2	BYTSREM	Remaining bytes on track. Number of bytes remaining on the track upon which the last record entry was written.
20(14)	2	TRKCAP	Total bytes on track. Number of bytes that can be written on a track of the volume containing SYS1.LOGREC.
22(16)	7	LASTTR	Address of last record written. Track address (in BBCCHHR format) of last record written on SYS1.LOGREC.
29(1D)	2	TRKSPER	Highest addressable track for each cylinder on volume containing SYS1.LOGREC.
31(1F)	2	EWMCNT	Warning count. Number of bytes remaining on early-warning-message track of SYS1.LOGREC when 90%-full point of data set is reached. When this is detected by a recording routine, it issues a message and turns on the early-warning-message switch at displacement 38.
33(21)	1	DEVCODE	Device code, indicating the device type of the volume on which SYS1.LOGREC resides: Code Device 04 2302 07 2305 MOD II 09 3330 and 3333 MOD I or 3350 operating in 3330-1 compatibility mode 0A 3340 and 3344 0B 3350 native mode 0C 3375 0D 3330 and 3333 MOD II or 3350 operating in 3330-II compatibility mode 0E 3380 0F 3390
34(22)	4	EWMTRK	Early-warning-message track. Track address (in CCHH format) on which 90% full point for data set exists.
38(26)	1	EWMSW	Switch byte:
	1... ....		90%-full-point message has been issued. This switch is turned on by the recording routine detecting 90% full point and is turned off by IFCEREP1 when clearing SYS1.LOGREC.
	.xxx xxxx		Reserved.
39(27)	1	SFTYBYTS	Check byte. Each bit in this field is set to 1; the field is used to check the validity of the header-record identifier.