Skip to main content

Retrieves the geometry information for the device.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
 (HANDLE) hDevice,            // handle to device 
 NULL,                        // lpInBuffer
 0,                           // nInBufferSize
 (LPVOID) lpOutBuffer,        // output buffer 
 (DWORD) nOutBufferSize,      // size of output buffer 
 (LPDWORD) lpBytesReturned,   // number of bytes returned 
 (LPOVERLAPPED) lpOverlapped  // OVERLAPPED structure 



A handle to the object on which the operation is to be performed. To retrieve a device handle, call the CreateFile function.


The control code for the operation. Use IOCTL_STORAGE_READ_CAPACITY for this operation.


Not used with this operation; set to NULL.


Not used with this operation; set to zero.


A pointer to a buffer that will receive a STORAGE_READ_CAPACITY structure specifying sizes for the specified device.


The size of the output buffer, in bytes. This buffer must be large enough to contain a STORAGE_READ_CAPACITY structure.


A pointer to a variable that receives the size of the data stored in the output buffer, in bytes.

If the output buffer is too small to receive any data, the call fails, GetLastError returns ERROR_INSUFFICIENT_BUFFER, and lpBytesReturned is zero.

If lpOverlapped is NULL, lpBytesReturned cannot be NULL. Even when an operation returns no output data and lpOutBuffer is NULL, DeviceIoControl makes use of lpBytesReturned. After such an operation, the value of lpBytesReturned is meaningless.

If lpOverlapped is not NULL, lpBytesReturned can be NULL. If this parameter is not NULL and the operation returns data, lpBytesReturned is meaningless until the overlapped operation has completed. To retrieve the number of bytes returned, call GetOverlappedResult. If hDevice is associated with an I/O completion port, you can retrieve the number of bytes returned by calling GetQueuedCompletionStatus.


A pointer to an OVERLAPPED structure.

If hDevice was opened without specifying FILE_FLAG_OVERLAPPED, lpOverlapped is ignored.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, the operation is performed as an overlapped (asynchronous) operation. In this case, lpOverlapped must point to a valid OVERLAPPED structure that contains a handle to an event object. Otherwise, the function fails in unpredictable ways.

For overlapped operations, DeviceIoControl returns immediately, and the event object is signaled when the operation has been completed. Otherwise, the function does not return until the operation has been completed or an error occurs.

Return value

If the operation completes successfully, DeviceIoControl returns a nonzero value.

If the operation fails or is pending, DeviceIoControl returns zero. To get extended error information, call GetLastError.

Return codeDescription

The operation was successful.


The system was unable to get the information from the device.


A memory allocation failed.


The output buffer size specified in nOutBufferSize is not large enough to hold the STORAGE_READ_CAPACITY structure.



Minimum supported client

Windows Vista

Minimum supported server

Windows Server 2008, Windows Server 2003 with SP1


WinIoCtl.h (include Windows.h)

See also

Device Management Control Codes