25 Apr
2018
25 Apr
'18
11:17 p.m.
On 4/24/18, Greg 'groggy' Lehey <grog(a)lemis.com> wrote:
"LBA" is newer than the time we're talking of. In those days, disk
data was addressed physically, by cylinder, head and sector, terms
that only died out round the turn of the century.
IBM DASD--Direct Access Storage Device, a term that encompassed drums,
disks and the data cell drive--addressed data on the media physically
by bin, cylinder, head, and record, as a hexadecimal number BBCCHHR.
Bin number was zero except on the IBM 2321 data cell drive. CKD
drives supported a variable number of records on each track, hence the
term "record" rather than "sector".
Logical block addressing (LBA) for sector-oriented disks allowed the
OS (or later, the disk controller) to hide bad block replacement from
programs.
VAX/VMS used a protected system file ([sysexe]badblock.sys) to keep
track of the bad blocks on each disk volume. DEC once got a customer
bug report complaining that if a privileged user gave the command
"TYPE SYS$SYSTEM:BADBLOCK.SYS", the console logged bad block errors.
How does/did Unix handle bad block replacement?
-Paul W.