Below is a table comparing all Raspberry Pi updated as of 2021. The includes every Raspberry Pi apart from the Pico Microcontroller.
|All Raspberry Pi||Raspberry Pi||Raspberry Pi 2||Raspberry Pi 3||Raspberry Pi 4||Raspberry Pi 400|
|Released||February 2012||February 2015||February 2016||June 2019||Nov 2020|
|CPU||ARM1176JZF-S||ARM Cortex-A7||ARM Cortex-A53||ARM Cortex-A72||ARM Cortex-A72|
|CPU speed||700MHz single core||900MHz quad core||1.2GHz quad core||1.5Ghz quad core||1.8Ghz quad core|
|RAM||512MB 256MB Rev 1||1GB||1GB||2gb, 4gb, 8gb||4gb|
|GPU||Broadcom Videocore IV||Broadcom Videocore IV||Broadcom Videocore IV||Broadcom Videocore VI||Broadcom Videocore VI|
|Storage||SDHC slot MicroSDHC Model A+ and B+||MicroSDHC slot||MicroSDHC slot||MicroSDHC slot||MicroSDHC slot|
|USB Ports||2 on Model B||4||4||4 (2 are USB 3.0)||4 (2 are USB 3.0)|
|WiFi||No built-in wifi||No built-in wifi||802.11n and Bluetooth 4.1||802.11n (dual band 5ghz) and Bluetooth 4.1||802.11n (dual band 5ghz) and Bluetooth 4.1|
|Power||Micro USB||Micro USB||Micro USB||USB-C||USB-C|
So which would you buy in 2021? Well, the Pi 1, 2, and 3 are highly underpowered yet cheap to buy on eBay, but if you want to spend a little extra you could get a Raspberry Pi 4 which is still cheap and offers great performance. There is a massive jump in performance from the older Pi and Pi 2 with the Pi 3 and above, so if you are going to buy a Raspberry Pi, you should most likely buy a Raspberry Pi 3 or above. You can buy Raspberry Pi from here: https://www.raspberrypi.org/products/
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