The pins number 2 and 3 in the VFQFPN36 package, and 5 and 6 in the LQFP48 and LQFP64 packages are configured as
OSC_IN/OSC_OUT after reset, however the functionality of PD0 and PD1 can be remapped by software on these pins. For the LQFP100 package, PD0 and PD1 are available by default, so there is no need for remapping. For more details, refer to the Alternate function I/O and debug configuration section in the STM32F10xxx reference manual.
The use of PD0 and PD1 in output mode is limited as they can only be used at 50 MHz in output mode.