.3 SD Card Slot
Raspberry Pi supports SD card which is a type of flash memory for a storage device for installing operating system or storing necessary data. The SD card has less capacity and performance than a hard disk, but it has the advantage that it consumes less power than a normal hard disk.
In Raspberry Pi, an SD card has a special meaning, unlike in other computer systems. When Raspberry Pi is powered up and started for the first time, a special program called Boot Loader is supposed to read the operating system installed on Raspberry Pi from the SD card. If you do not have an SD card or you do not have the proper operating system installed on your SD card, you can not start the Raspberry Pi system.