Subfamilies include the H8/300, H8/300H, H8/500, and H8S series, each with dozens of different parts, varying by speed, selection of builtin peripherals such as timers and serial ports, and amounts of ROM and RAM. Builtin ROM tends to range from 16K to 128K bytes, and RAM from 512 to 4K bytes.
The basic architecture of the H8 is patterned after the DEC PDP-11, with eight 16-bit registers (the H8/300H and H8/S have an additional bank of eight registers), and a variety of addressing modes. Several companies provide compilers for the H8 family, and there is a complete GNU port, including a simulator. There are also various hardware emulators available.