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mg_notes:cpm:softcard_cpm_ref [2019/09/30 18:04] M.G. [The Apple CP/M Disk Parameter Tables] |
mg_notes:cpm:softcard_cpm_ref [2019/09/30 18:28] M.G. [The Apple CP/M Disk Parameter Tables] |
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| ^ Offset ^ Contents ^ Use ^ | ^ Offset ^ Contents ^ Use ^ | ||
| - | | 00H | SPT 16b | Total number of sectors per track | | + | | 00H | SPT 16b | Total number of 128-byte sectors per track | |
| - | | 02H | BSH 8b | Data allocation block shift factor, determined by the data block allocation size | | + | | 02H | BSH 8b | Data allocation block shift factor, determined by the data block allocation size \\ 3 -> 1K, 4 -> 2K, 5 -> 4K, ... | |
| - | | 03H | BLM 8b | Data allocation block mask (2[BSH-1]) | | + | | 03H | BLM 8b | Data allocation block mask (2[BSH-1]) \\ 7 -> 1K, 0FH -> 2K, 01FH -> 4K, ... | |
| | 04H | EXM 8b | Extent mask, determined by data block allocation size and number of disk blocks | | | 04H | EXM 8b | Extent mask, determined by data block allocation size and number of disk blocks | | ||
| - | | 05H | DSM 16b | Total storage capacity of disk drive | | + | | 05H | DSM 16b | Total storage capacity of disk drive, blocks minus one | |
| | 07H | DRM 16b | Total number of directory entries minus one | | | 07H | DRM 16b | Total number of directory entries minus one | | ||
| - | | 09H | AL0 8b | Determines reserved directory blocks | | + | | 09H | AL0 8b | Directory allocation bitmap, byte 0. | |
| - | | 0AH | AL1 8b | Determines reserved directory blocks | | + | | 0AH | AL1 8b | Directory allocation bitmap, byte 1. | |
| | 0BH | CKS 16b | Size of directory check vector | | | 0BH | CKS 16b | Size of directory check vector | | ||
| | 0DH | OFF 16b | No of reserved tracks at beginning of logical disk | | | 0DH | OFF 16b | No of reserved tracks at beginning of logical disk | | ||
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| bit of AL1, 15=lo bit of AL1. Bits are assigned starting at bit 0 up | bit of AL1, 15=lo bit of AL1. Bits are assigned starting at bit 0 up | ||
| until bit 15. Suppose nbits is the number of bits set to 1: | until bit 15. Suppose nbits is the number of bits set to 1: | ||
| + | |||
| + | |||
| ^ BLS ^ Directory entries ^ | ^ BLS ^ Directory entries ^ | ||
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| | 16384 | 512 * nbits | | | 16384 | 512 * nbits | | ||
| - | Example: if DRM=127 (128 directory entries) and BLS=1024 bytes, there | + | Example: |
| + | |||
| + | ^ ^ AL0 ^^^^^^^^ AL1 ^^^^^^^^ | ||
| + | ^ Bit ^ 7 ^ 6 ^ 5 ^ 4 ^ 3 ^ 2 ^ 1 ^ 0 ^ 7 ^ 6 ^ 5 ^ 4 ^ 3 ^ 2 ^ 1 ^ 0 ^ | ||
| + | | | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | | ||
| + | |||
| + | If DRM=127 (128 directory entries) and BLS=1024 bytes, there | ||
| are 32 directory entries per block, requiring 4 reserved blocks. Thus | are 32 directory entries per block, requiring 4 reserved blocks. Thus | ||
| the 4 hi bits if AL0 are set, and AL0=0FH, AL1=00H | the 4 hi bits if AL0 are set, and AL0=0FH, AL1=00H | ||