Bytes per sector in IDENTIFY DEVICE

The following uses PIO and should work for 16 or 32 bit:
Defs

Code:

ATA_REG_DATA                                    equ 0x0000 ; RW Data
ATA_REG_COMMAND                                 equ 0x0007 ;  W Command
ATA_REG_STATUS                                  equ 0x0007 ; R  Status
ATA_COMMAND_IDENTIFY_DEVICE                     equ 0xEC
ATA_STATUS_BUSY                                 equ 0x80

struct ATAPI_IDENTIFY
    Config                  dw ?
    Cylinders               dw ? ; OBSOLETE
    Reserved0               dw ?
    Heads                   dw ? ; OBSOLETE
    BytesPerTrack           dw ?
    BytesPerSector          dw ?
    SectorsPerTrack         dw ? ; OBSOLETE
    Vendor0                 dw ?
    Vendor1                 dw ?
    Vendor2                 dw ?
    Serial0                 dw ?
    Serial1                 dw ?
    Serial2                 dw ?
    Serial3                 dw ?
    Serial4                 dw ?
    Serial5                 dw ?
    Serial6                 dw ?
    Serial7                 dw ?
    Serial8                 dw ?
    Serial9                 dw ?
    BufferType              dw ?
    BufferSize              dw ?
    ECCBytes                dw ?
    Firmware0               dw ?
    Firmware1               dw ?
    Firmware2               dw ?
    Firmware3               dw ?
    ModelName0              dw ?
    ModelName1              dw ?
    ModelName2              dw ?
    ModelName3              dw ?
    ModelName4              dw ?
    ModelName5              dw ?
    ModelName6              dw ?
    ModelName7              dw ?
    ModelName8              dw ?
    ModelName9              dw ?
    MulSecPerInt            dw ?
    DWIO                    dw ?
    LBADMA                  dw ?
    Reserved1               dw ?
    PIOMode                 dw ?
    DMAMode                 dw ?
    Reserved2               dw ?
    ApCylinders             dw ?
    ApHeads                 dw ?
    ApSectorsPerTrack       dw ?
    Capacity0               dw ?
    Capacity1               dw ?
    NumSecPerInt            dw ?
    LBASectors0             dw ?
    LBASectors1             dw ?
    SinDMAModes             dw ?
    MulDMAModes             dw ? ;54
    Reserved3               rw 64
    Vendor3                 rw 32
    Reserved4               rw 96
    Reserved5               rw 10
ends

Code

Code:

;mov bp,xxx ; The legacy ATA base is 0x0170 or 0x01F0 but this can also be acquired from PCI information (BAR registers)

; Write command
mov al,ATA_COMMAND_IDENTIFY_DEVICE
lea dx,[bp+ATA_REG_COMMAND]
out dx,al

; Wait idle
@@: ; wait

in al,dx ; dx is also ATA_REG_STATUS

test al,ATA_STATUS_BUSY
jnz @b ; wait

test al,ATA_STATUS_ERROR
jnz @f ; error

; Copy data
mov cx,(sizeof.ATAPI_IDENTIFY / 2) ; 2 bytes per read
lea dx,[bp+ATA_REG_DATA]
mov di,buffer
cld
rep insw ; 2 bytes per read

; You can now read buffer.BytesPerSector
;end
@@: ; error
;end

ATAPI_IDENTIFY buffer

Hope that helps