HP 20 series
The pocket calculators of the "Twenties" series are the second generation of pocket calculators from Hewlett-Packard and appeared on the market in 1975. According to a strict design, this series comprises six computers, and eleven after incorporating technologically similar models. All computers have a twelve-digit LED display and are powered by rechargeable NiCd cells, which can be clipped into the rear housing shell made of light-colored plastic.
The computers use reverse Polish notation (UPN) as the input method . This series also introduced the characteristic trapezoidal keys, on the sloping front of which an additional print could be placed.
Models
The series includes the following models (with the year of their production):
- HP-10 - A simple addition machine with a printer
- HP-21 - basic model; Mathematical and scientific calculator and successor to the HP-35 (1975–1978)
- HP-22 - basic model for commercial use (1975–1978)
- HP-25 - Programmable mathematical and scientific pocket calculator (1975–1978)
- HP-25C - Programmable mathematical and scientific pocket calculator with "Constant Memory" (1976–1978)
- HP-27 - "Do everything", pocket calculator with a selection of commercial and technical-scientific functions (1976–1978)
- HP-29C - Programmable mathematical and scientific pocket calculator with "constant memory" for high requirements (1977–1979)
In a broader sense (with partly different equipment, functions and housing concept), this generation also includes:
- HP-19C - enlarged pocket calculator, functions like the HP-29C, additionally with a built-in printer for thermal paper (1977–1979)
- HP-91 - desktop calculator with thermal printer for mathematical and scientific applications (1976–1979)
- HP-92 - Counterpart to HP-91 for commercial applications (1977–1980)
- HP-67 - Programmable top model with built-in card reader and successor to the HP-65 (1976–1982)
- HP-97 (S) - Programmable table model of the HP-67 with built-in card reader and printer ('S' with a controllable interface) (1976–1984)
The HP-95C should also be mentioned, a version of the HP-25C with a print function that is considerably expanded in terms of functionality. However, only a very small number of this device was produced and for market policy reasons (especially to avoid internal competition with the HP-97) it was never put on the market, so that only a few copies still exist.
The HP-10
The HP-10 is probably the simplest calculator that HP has ever built. It had the four basic arithmetic operations , a memory (M) and a percentage calculation . The operating logic of the computer corresponds to the simple calculating machines that are still common today for accounting purposes. The particular benefit lay in the integrated printer on the one hand and the compact, network-independent design on the other. The printing mechanism, essential elements of the housing, power supply and thermal paper correspond to those of the HP-19C.
The HP-21
The actual basic model had the essential mathematical and scientific functions and also allowed coordinate conversion (right-angled to polar and vice versa) as well as memory arithmetic.
The HP-22
The HP-22 was the simple commercial model in the range. Compared to the HP-70, the calculation of accumulated interest, the remaining balance, statistical functions and additional memory were added.
The HP-25
The HP-25 was programmable, which required a triple assignment of the keys, although the third function was not actually used on all keys. Program steps were organized efficiently so that an operation of two or three keys only occupied one of the 49 possible program steps ('merged keystrokes'). There were no subroutines and labels on this model, only jumps to absolute line numbers were possible. A manual was published for the HP-25 with programs for a large number of problems, which were repeatedly adapted for later models. The computer competed with the TI-58 and TI-58C models in its time and was a little more expensive, but also more robust and durable than these.
In the later, otherwise functionally identical HP-25C model based on CMOS technology, the memory content was retained when the device was switched off. Its appearance on the market led to a price reduction of the HP-25.
The HP-27
This model, intended as a compromise, equipped with the respective elementary commercial and technical-scientific functions and also with triple assignment of the keys, did not establish itself well on the market and is accordingly rare today.
HP-19C, HP-29C
Both computers were the top models in the series, each with 98 program steps and 30 memories, commands for loop control (ISZ and DSZ), subroutines (three levels) and labels, indirect addressing with the i-register of addresses (GTO i / GSB i) and registers (STO i / RCL i) and improvements when changing programs.
The “C” in the model name stood for “continuous memory”: programs, stacks and the content of the first 16 memory registers were retained even when the device was switched off. The variety of functions and the elaborate production of circuits led to a comparatively high introductory price for the devices in this series, for example 195 US dollars for the HP-29C. In Germany the HP-29C cost 575 marks.
The HP-19C (1977–1979) essentially differed in the printing mechanism and the additional commands required for it. Key spacing and key size corresponded to the 29C, so it was not a desktop calculator.
Other models
- HP-91 - desktop calculator with thermal printer for mathematical and scientific applications (1976–1979)
- HP-92 - Counterpart to HP-91 for commercial applications (1977–1980)
- HP-67 - top model with built-in card reader and successor to the HP-65 (1976–1982)
- HP-97 (S) - table model of the HP-67 with built-in printer (and a controllable interface) (1976–1984)
The models HP-27S, HP-22S and HP-20S (an AOS computer) , which appeared in the 1980s and 1990s, as well as the HP-10C from the " Voyager " series and the later HP 10S are not included this family.
Manufacturing technology and successor
The computers of the "twenties" series coincide with the development of CMOS technology. The PMOS technology used up to that point was tried and tested and cheap, but only enabled moderate packing densities and, due to its high quiescent current, did not allow permanent storage. NMOS circuits were used for the HP-27 until CMOS technology was used for the HP-25C and HP-29C. The case was built in such a way that it was held together with just two screws hidden under the lower rubber feet. During this time pocket calculator sales began to exceed the million mark, which made such manufacturing optimizations necessary.
The successors to these computers are the 30 series computers .
Web links
- HP 20 Series Technology and Packaging - Museum of HP Calculators