11.6 LBA (Logical Block Address)

When disk blocks are actually to be accessed, the 64DD library assigns a serial number to each block, beginning with 0, and uses these numbers for access. This number is called a logical block address (LBA). Because each disk has 4,292 blocks, the LBAs range from 0 to 4291. These numbers are assigned according to the following rules.

  1. ROM area first, then RAM area

  2. Head 0 first, then head 1

  3. Periphery first for head 0, center first for head 1

The following example is for a disk of Type 0.

  1. Numbering starts from the outermost circumference of zone 0 for head 0, which is assigned LBA0 and LBA1. With a Type 0 disk, the zones up to Zone 2 for head 0 are ROM area, with 268 blocks in Zone 0, 292 blocks in Zone 1, and 274 blocks in Zone 2. Thus, the LBA for the innermost circumference/sector of Zone 2 is 833 (268+292+274-1). (Because there are 2 blocks in each circumference, there are actually 2 LBAs for the innermost circumference of Zone 2, 832 and 833.)

  2. The next numbers are assigned to the bottom side of the disk. The innermost circumference of Zone 2 for head 1 is labeled LBA834 and 835, and the numbers increase as the locations become more peripheral. Both Zone 2 and Zone 1 have 292 blocks, so the LBAs of the outermost circumference/sector of Zone 1 are 1417 (834+292+292-1) and 1416 (same rationale). The last ROM area LBA is 1417.

  3. The first LBA of the RAM area, 1418, is in the outermost circumference of Zone 3 for head 0. The numbers increase as the locations become more central. For head 0, there are 274 LBAs in zones 3-6 and 204 in Zone 7. Thus, the LBAs for the innermost circumference for head 0 are 2717 (1418+274*4+204-1) and 2716.

  4. The next block (LBA2718) is in the innermost circumference of Zone 8 for head 1. The numbers increase as the locations become more peripheral. For head 1, there are 274 LBAs in Zones 3-7 and 204 in Zone 8. Thus, the LBAs for the outermost circumference of Zone 3 for head 1 are 4291 (2718+274*5+204-1) and 4290.

LBA Map
ROM area
RAM area

Disk Type 0 Disk Type 1 Disk Type 2
Zone Head 0 Head 1 Head 0 Head 1 Head 0 Head 1
0 0-267 0-267 0-267
1 268-559 1126-1417 268-559 1674-1965 268-559 2222-2513
2 560-833 834-1125 560-833 1382-1673 560-833 1930-2221
3 1418-1691 4018-4291 834-1107 1108-1381 834-1107 1656-1929
4 1692-1965 3744-4017 1966-2239 4018-4291 1108-1381 1382-1655
5 1966-2239 3470-3743 2240-2513 3744-4017 2514-2787 4018-4291
6 2240-2513 3196-3469 2514-2787 3470-3743 2788-3061 3744-4017
7 2514-2717 2922-3195 2788-2991 3196-3469 3062-3265 3470-3743
8 2718-2921 2992-3195 3266-3469

Disk Type 3 Disk Type 4 Disk Type 5
Zone Head 0 Head 1 Head 0 Head 1 Head 0 Head 1
0 0-267 0-267 0-267
1 268-559 2770-3061 268-559 3318-3609 268-559 3796-4087
2 560-833 2478-2769 560-833 3026-3317 560-833 3504-3795
3 834-1107 2204-2477 834-1107 2752-3025 834-1107 3230-3503
4 1108-1381 1930-2203 1108-1381 2478-2751 1108-1381 2956-3229
5 1382-1655 1656-1929 1382-1655 2204-2477 1382-1655 2682-2955
6 3062-3335 4018-4291 1656-1929 1930-2203 1656-1929 2408-2681
7 3336-3539 3744-4017 3610-3813 4018-4291 1930-2133 2134-2407
8 3540-3743 3814-4017 4088-4291

Disk Type 6
Zone Head 0 Head 1
0 0-267
1 268-559 4000-4291
2 560-833 3708-3999
3 834-1107 3434-3707
4 1108-1381 3160-3433
5 1382-1655 2886-3159
6 1656-1929 2612-2885
7 1930-2133 2338-2611
8 2134-2337