Sector Addressing Mode; Logical Chs Addressing Mode; Lba Addressing Mode - IBM DTLA-305040 - Deskstar 41.1 GB Hard Drive Specifications

10.3 Sector Addressing Mode

All addressing of data sectors recorded on the drive media is by a logical sector address. The logical
CHS address for the drive is different from the actual physical CHS location of the data sector on the disk
media.
The drive supports both Logical CHS Addressing Mode and LBA Addressing Mode as the sector addres-
sing mode.
The host system may select either the currently selected CHS translation addressing or LBA addressing
on a command-by-command basis by using the L bit in the DEVICE/HEAD register. So a host system
must set the L bit to 1 if the host uses LBA Addressing mode.

10.3.1 Logical CHS Addressing Mode

The logical CHS addressing is made up of three fields: cylinder number, head number and sector
number. Sectors are numbered from 1 to the maximum value allowed by the current CHS translation
mode but cannot exceed 255(0FFh). Heads are numbered from 0 to the maximum value allowed by the
current CHS translation mode but cannot exceed 15(0Fh). Cylinders are numbered from 0 to the maxi-
mum value allowed by the current CHS translation mode but cannot exceed 65535(0FFFFh).
When the host selects a CHS translation mode using the INITIALIZE DEVICE PARAMETERS command,
the host requests the number of sectors per logical track and the number of heads per logical cylinder.
The device then computes the number of logical cylinders available in requested mode.
The default CHS translation mode is described in the Identify Device Information. The current CHS trans-
lation mode is also described in the Identify Device Information.

10.3.2 LBA Addressing Mode

Logical sectors on the device shall be mapped linearly with the first LBA addressed sector (sector 0) be-
ing the same sector as the first logical CHS addressed sector ( cylinder 0, head 0, sector 1). Regardless
of the logical CHS translation mode currently in effect, the LBA address of a given logical sector does not
change. The following formula is always true:
LBA = ((cylinder * heads per cylinder + heads) * sectors per track) + sector – 1
where heads per cylinder and sectors per track are the current translation mode values
On LBA addressing mode the LBA value is set to the following register:
Device/Head
Cylinder High
Cylinder Low
Sector Number <--- LBA bits 7-0
<--- LBA bits 27-24
<--- LBA bits 23-16
<--- LBA bits 15-8
Deskstar 40GV & 75GXP hard disk drive specifications
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