Introduced at US$395 (equivalent to $2,900 in 2023),[2] like HP's first scientific calculator, the desktop 9100A, it used reverse Polish notation (RPN) rather than what came to be called "algebraic" entry.

Internally, the calculator was organized around a serial (1-bit) processor chipset dual sourced under contract from Mostek and American MicroSystems Inc (pictured), processing Decimal floating point numbers with 10 digit mantissa and 2 digit exponent, stored in 14 nibble (56 bit) numbers as BCD including two nibbles for the signs.

The HP-25 was a smaller, cheaper model of a programmable scientific calculator without magnetic card reader, with features much like the HP-65.

The HP-41C was a major advance in programmability and capacity, and offered CMOS memory so that programs were not lost when the calculator was switched off.

Four external ports below the display area allowed memory expansion (RAM modules), loading of additional programs (ROM modules) and interfacing a wide variety of peripherals including HP-IL ("HP Interface Loop"), a scaled-down version of the HPIB/GPIB/IEEE-488 instrument bus.