Error Rate Test (Ert) Log - HP 7957A Hardware Manual

Service Information
7957 A/7958A
The 'estimate' is given to the count for several reasons. The count is not kept on
an individual head basis as is the case for the ERT sectors read count. The run
time sectors read count is a total for all heads, which is divided by the total
number of heads, to give an estimate of the number of sectors read by an
individual head.
The count is also compromised by the fact that it is initially kept in RAM. The
count is only moved to a more permanent location (maintenance track or
EEPROM) when a run time marginal/unrecoverable data error occurs or the
utility command PRESET is issued. Therefore, if power is lost before the RAM
based count is added to the EEPROM based count, an inaccuracy equal to the
RAM based count occurs.
Note: Reading the run time error log also updates the EEPROM count with the
total of the RAM based count and the EEPROM count.
4-46. Error Rate Test (ERT) Log
4-28
The RAM based ERT table will store data error information on a maximum of
50 locations.
The log is allocated in the following way:
sectors read head 0
sectors read head 1
5 bytes
5 bytes
sectors read head N*
5 bytes
*N =
4 for
HP
7957A (total
*N
7 for
HP
7958A (total
entry:physical cylinder
physical head
physical sector
logical cylinder
logical head
logical sector
error byte
occurrence count
-----------
80 bytes
bytes
=
25
bytes
=
40
2 bytes
1 byte
bytes)
bytes)
1 byte (equal logical sector)
2 bytes
1 byte
1 byte
1 byte
1 byte
10 bytes
50 entries
===>
500 bytes