6.2Address Translation
When the IDD receives any command which involves access to the disk medium, the IDD always implements the address translation from the logical address (a
Following subsections explains the CHS translation mode.
6.2.1Default parameters
In the logical to physical address translation, the logical cylinder, head, and sector addresses are translated to the physical cylinder, head, and sector addresses based on the number of heads and the number of sectors per track which are specified with an INITIALIZE DEVICE PARAMETERS command. This is called as the current translation mode.
If the number of heads and the number of sectors are not specified with an INITIALIZE DEVICE PARAMETERS command, the default values listed in Table 6.1 are used. This is called as the default translation mode. The parameters in Table 6.1 are called BIOS specification.
Table 6.1 Default parameters
| Formatted |
| Parameters (logical) |
| |
| capacity (MB) |
|
|
|
|
| Number of cylinders | Number of heads |
| Number of sectors/track | |
|
|
| |||
|
|
|
|
|
|
MPG3102AT | 10,248 | 16,383 | 16 |
| 63 |
|
|
|
|
|
|
MPG3153AT | 15,371 | − | − |
| − |
|
|
|
|
|
|
MPG3204AT | 20,496 | − | − |
| − |
|
|
|
|
|
|
MPG3307AT | 30,743 | − | − |
| − |
|
|
|
|
|
|
MPG3409AT | 40,992 | − | − |
| − |
|
|
|
|
|
|
As long as the formatted capacity of the IDD does not exceed the value shown on Table 6.1, the host can freely specify the number of cylinders, heads, and sectors per track.
Generally, the device recognizes the number of heads and sectors per track with the INITIALIZE DEVICE PARAMETER command. However, it cannot recognizes the number of cylinders. In other words, there is no way for the device to recognize a host access area on logical cylinders. Thus the host should manage cylinder access to the device.
The host can specify a logical address freely within an area where an address can be specified (within the specified number of cylinders, heads, and sectors per track) in the current translation mode.
The host can read an addressable parameter information from the device by the IDENTIFY DEVICE command (Words 54 to 56).
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