I have my laptops old 2TB 5400RPM HDD laying around and I was wondering if could maybe use it instead of a micro SD card since it has much more space, and it also might be quicker.
As Ed has mentioned, it is possible to load the operating system from an external device such as an HDD or a flash drive. Unfortunately, the RPi will still require a microSD card as a limitation of the SOC. This is a fundamental part to how it functions, and there is no way of getting around it.– Jacobm001Apr 27, 2016 at 15:41
Yes, but it will still require a microSD, I rigged up an SSD to my Raspberry Pi using a USB to SATA Converter USB converter.
In regards to setting it up, I plugged the SSD into the adapter, then plugged the data cable into the Pi with the extra power cable into a spare USB port on my hub.
Then I installed Berryboot onto my microSD and turned on my Pi (Making sure everything is plugged in). Then, Berryboot will ask where you wish to install your OS and you then select the HDD (It might come up as a USB since it's plugged into the USB port). After that just install an OS and everything will be saved to your HDD instead of your SD card.
But it will still require your SD card to boot into your Pi OS, unfortunately.