From Wikipedia:
The Casio FX-850P is a scientific calculator introduced in 1987 and sold until 1992.
Specifications
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2 lines with 32 5×7 characters LCD
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(some indicators and a 5 digit 7-segment display)
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8 KB RAM (FX-860P: 24 KB, FX-880P: 32 KB)
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CPU: VLSI at 1,228MHz. Hitachi HD62002A01 (FX-860P, FX880P: HD62002A03)
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Integrated speaker
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Internal slot for memory expansion (32 KB)
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Connector with support for RS232 and Centronics (only level converter for RS232, Centronics needed)
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LCD Driver: 2 x HD66100F
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2x 3V CR2032 lithium batteries as main power supply
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1x 3V CR1220 lithium battery as memory backup (RAM power supply)
User's manual at http://www.usersmanualguide.com/casio/calculators/fx-850p
The calculator had a BASIC interpreter, MEMO function, a formula library. The built-in 8 kB memory could be expanded using the optional Casio RP-8 (8 kB) or RP-33 (32 kB) RAM expansion modules. An optional Casio FA-6 interface board provided a cassette tape recorder connector, a Centronics printer connector and an RS-232C port. The calculator could print data and listings on any Centronics printer; printing graphics required the Casio FP-100 plotter-printer.