HP Saturn

The Saturn family of 4-bit microprocessors was developed by Hewlett-Packard in the 1980s for programmable scientific calculators/microcomputers. It succeeded the Nut family of processors used in earlier calculators. The original Saturn chipset was first used in the HP-71B hand-held BASIC-programmable computer, introduced in 1984. Later models of the family powered the popular HP 48 series of calculators, among others. The HP 49 series initially used the Saturn CPU as well, until the NEC fab could no longer manufacture the processor for technical reasons in 2003. Therefore, starting with the HP 49g+ model in 2003, the calculators switched to use a Samsung S3C2410 processor with ARM920T core (part of the ARMv4T architecture) to run an emulator of the Saturn architecture in software. In 2000, the HP 39G and HP 40G were the last calculators introduced based on the Saturn hardware. The last calculators based on the Saturn emulator were the HP 39gs, HP 40gs and HP 50g in 2006, as well as the 2007 revision of the hp 48gII. The HP 50g, the last calculator utilizing this emulator, was discontinued in 2015 when Samsung stopped producing the ARM processor it was based on.

The Saturn architecture is nibble-based; that is, the core unit of data is 4-bit-sized, which can hold one binary-coded decimal (BCD) digit.

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