Getting Started with Teensy
Chowdah 
Introduction
The Teensy 4.x series offers some of the greatest performance and flexibility available on any microcontroller platform. Powered by a 600MHz Arm Cortex-M7 microcontroller with dual-issue superscalar architecture, branch prediction, and tightly-coupled memory, up to two instructions and memory accesses per cycle accelerate operation beyond the already blistering clock pace. A hardware Floating Point Unit (FPU) executes complex float and double precision mathematical calculations at full hardware speed.
The compact Teensy 4.0 offers 40 I/O pins (including bottom SMT pads; 24 pins are breadboard-able) with 2MB of Flash memory. The larger Teensy 4.1 increases the I/O pin count to 55 (42 beadboard-able) and adds a microSD slot, 5-pin USB host with power management (requires USB Host Cable, sold separately), Ethernet port (requires Ethernet Kit), and PSRAM expansion (8MB chips sold separately), plus a plentiful 8MB of Flash. Extensive support libraries and an enthusiastic community make Teensy a popular choice for embedded projects of all kinds.