AVR is the name of the family of microcontrollers designed by the Atmel company and introduced to the market in 1996. They designed these microcontrollers with the RISC command set on the modified Harvard architecture.
Microcontrollers are 8-Bit and, as an exception, it produced in 32-bit models in a period. It is one of the most widely used microcontrollers in many embedded systems and especially in hobby circuits, and forms the basis of Arduino.
- Supports alternate serial ports, CPU frequencies, and baud rates.
Optiboot (an older version) is installed by default on Arduino Uno and (as of 2018) Arduino Nanos and can be installed on all older mega8, 168, or 328 based Arduinos.
If you want to review Optiboot’s wiki or review their code, you can find the github link here.
ATmega chip in short:
ATmega chip is a high-performance, low-power 8-Bit microcontroller. It has different sizes of EEPROM, SRAM, and FLASH memory. It can read and write to FLASH memory up to 10,000 times but has a powerful command that runs in 131 majority single cycles. In ATmega sleep mode, it draws a standby current of 0.1 uA.