Question

int 13h与ah=02h的顺序是什么，将从19开始读取(C, H, S) = (0, 0, 1)扇区，条件是（软盘）磁盘几何结构为2磁头，每磁道18个扇区和80个扇区每边都跟踪。

或更笼统地说，当磁道到达磁道0的头0时会发生什么？它会追踪1还是朝向1？在这种情况下，它甚至还能正常工作吗？

编辑：等等。这实际上是小时，分钟，秒吗？如果我们到达曲目的结尾（S大于18），那么H会增加吗？

Answer 1

现代BIOS支持多磁道读写的概念，如果您在磁道末尾读取或写入，它将继续以下磁道。为了与最广泛的BIOS（旧的和新的）最兼容，您可能希望考虑不要跨越磁道边界进行读取或写入。

驱动器几何结构为每磁道18个扇区/ 2个磁头/ 80个柱面（软盘3.5英寸1.44MB），CHS（0,0,18）之后的扇区为CHS（0,1,1）。在CHS（0,1,18）处的下一个扇区是CHS（1,0,1）。在某种程度上，它类似于HH：MM：SS。

根据驱动器的几何形状，共有2880（80 * 2 * 18）个扇区。如果将扇区编号为0到2879（含），则将它们称为逻辑块地址（LBA）。

Int 13h/ah=2采用 CHS 值。您可以使用以下公式（或等效公式）将 LBA 转换为 CHS 值：

C = (LBA ÷ SPT) ÷ HPC
H = (LBA ÷ SPT) mod HPC
S = (LBA mod SPT) + 1

HPC = Heads per cylinder (aka Number of Heads)
SPT = Sectors per Track, 
LBA = logical block address

"mod" is the modulo operator (to get the remainder of a division)

我在将LBA转换为CHS 的其他Stackoverflow answer中已经写了关于 LBA 至 CHS 计算的更多信息。。如果使用这些计算创建了表格，则编号将如下所示：

LBA =    0:   CHS = ( 0,  0,  1)
LBA =    1:   CHS = ( 0,  0,  2)
LBA =    2:   CHS = ( 0,  0,  3)
LBA =    3:   CHS = ( 0,  0,  4)
LBA =    4:   CHS = ( 0,  0,  5)
LBA =    5:   CHS = ( 0,  0,  6)
LBA =    6:   CHS = ( 0,  0,  7)
LBA =    7:   CHS = ( 0,  0,  8)
LBA =    8:   CHS = ( 0,  0,  9)
LBA =    9:   CHS = ( 0,  0, 10)
LBA =   10:   CHS = ( 0,  0, 11)
LBA =   11:   CHS = ( 0,  0, 12)
LBA =   12:   CHS = ( 0,  0, 13)
LBA =   13:   CHS = ( 0,  0, 14)
LBA =   14:   CHS = ( 0,  0, 15)
LBA =   15:   CHS = ( 0,  0, 16)
LBA =   16:   CHS = ( 0,  0, 17)
LBA =   17:   CHS = ( 0,  0, 18)
LBA =   18:   CHS = ( 0,  1,  1)
LBA =   19:   CHS = ( 0,  1,  2)
LBA =   20:   CHS = ( 0,  1,  3)
LBA =   21:   CHS = ( 0,  1,  4)
LBA =   22:   CHS = ( 0,  1,  5)
LBA =   23:   CHS = ( 0,  1,  6)
LBA =   24:   CHS = ( 0,  1,  7)
LBA =   25:   CHS = ( 0,  1,  8)
LBA =   26:   CHS = ( 0,  1,  9)
LBA =   27:   CHS = ( 0,  1, 10)
LBA =   28:   CHS = ( 0,  1, 11)
LBA =   29:   CHS = ( 0,  1, 12)
LBA =   30:   CHS = ( 0,  1, 13)
LBA =   31:   CHS = ( 0,  1, 14)
LBA =   32:   CHS = ( 0,  1, 15)
LBA =   33:   CHS = ( 0,  1, 16)
LBA =   34:   CHS = ( 0,  1, 17)
LBA =   35:   CHS = ( 0,  1, 18)
LBA =   36:   CHS = ( 1,  0,  1)
LBA =   37:   CHS = ( 1,  0,  2)
LBA =   38:   CHS = ( 1,  0,  3)
LBA =   39:   CHS = ( 1,  0,  4)
LBA =   40:   CHS = ( 1,  0,  5)
LBA =   41:   CHS = ( 1,  0,  6)

... [snip] ...

LBA = 2859:   CHS = (79,  0, 16)
LBA = 2860:   CHS = (79,  0, 17)
LBA = 2861:   CHS = (79,  0, 18)
LBA = 2862:   CHS = (79,  1,  1)
LBA = 2863:   CHS = (79,  1,  2)
LBA = 2864:   CHS = (79,  1,  3)
LBA = 2865:   CHS = (79,  1,  4)
LBA = 2866:   CHS = (79,  1,  5)
LBA = 2867:   CHS = (79,  1,  6)
LBA = 2868:   CHS = (79,  1,  7)
LBA = 2869:   CHS = (79,  1,  8)
LBA = 2870:   CHS = (79,  1,  9)
LBA = 2871:   CHS = (79,  1, 10)
LBA = 2872:   CHS = (79,  1, 11)
LBA = 2873:   CHS = (79,  1, 12)
LBA = 2874:   CHS = (79,  1, 13)
LBA = 2875:   CHS = (79,  1, 14)
LBA = 2876:   CHS = (79,  1, 15)
LBA = 2877:   CHS = (79,  1, 16)
LBA = 2878:   CHS = (79,  1, 17)
LBA = 2879:   CHS = (79,  1, 18)

读取比int 13h轨道更多的扇区

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