def pd_to_sd(pd):
    """
    Converts a device name from Windows' physical device ID (ie: pd0) to
    Linux's sda notation. Handles up to 'pd675' = 'sdzz'.

    ###Args:
    * **pd (int):** Physical device ID number.

    ##Returns:
    * **(str):** Linux-style 'sd_' device name.
    """
    try:
        pd = int(pd)
    except ValueError:
        return None
    pd2sd = {}
    for i in range(26):
        pd2sd[i] = chr(ord('a') + i)
    if pd > 26:
        first = pd // 26 - 1
        second = pd % 26
        return 'sd' + pd2sd[first] + pd2sd[second]
    else:
        return 'sd' + pd2sd[pd]
