System information

The BAD SECTOR message indicates that the disk controller electronics has detected an error
condition in reading or writing the disk. This condition is generally caused by a malfunctioning
disk controller or an extremely worn disk. If you find that CP/M reports this error more than once
a month, the state of the controller electronics and the condition of the media should be checked.
You can also encounter this condition in reading files generated by a controller produced by a
different manufacturer. Even though controllers claim to be IBM compatible, one often finds
small differences in recording formats. The MDS-800 controller, for example, requires two bytes
of ones following the data CRC byte, which is not required in the IBM format. As a result, disks
generated by the Intel MDS can be read by almost all other IBM-compatible systems, while disk
files generated on other manufacturers' equipment produce the BAD SECTOR message when
read by the MDS. To recover from this condition, press a CTRL-C to reboot (the safest course),
or a return, which ignores the bad sector in the file operation.
Note:pressing a return might destroy disk integrity if the operation is a directory write. Be sure
you have adequate back-ups in this case.
The SELECT error occurs when there is an attempt to address a drive beyond the range
supported by the BIOS. In this case, the value of d in the error message gives the selected drive.
The system reboots following any input from the console.
The READ ONLY message occurs when there is an attempt to write to a disk or file that has
been designated as Read-Only in a STAT command or has been set to Read-Only by the BDOS.
Reboot CP/M by using the warm start procedure, CTRL-C, or by performing a cold start
whenever the disks are changed. If a changed disk is to be read but not written, BDOS allows the
disk to be changed without the warm or cold start, but internally marks the drive as Read-Only.
The status of the drive is subsequently changed to Read-Write if a warm or cold start occurs. On
issuing this message, CP/M waits for input from the console. An automatic warm start takes
place following any input.
1.6 Transient Commands CP/M Operating System Manual
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