The HP 9625A: A Gateway to Computing at the University of Colombo in the 1970s - My First Experience

In 1975, Hewlett-Packard introduced the HP 9825A—a device marketed as a calculator but far more advanced than its competitors at the time. The Department of Mathematics at the University of Colombo was honoured to receive this impressive machine as a donation from the ODA UK in 1977. During my third year as a university student, I was privileged to work with the HP 9825A in my FORTRAN programming course. Under the expert guidance of Prof. V. K. Samaranayake (Sam) and with Dr Kevin Senevirathne (Kevin) as my tutor, I embarked on a journey of learning that profoundly impacted my technical education. This equipment, including the HP 9825A, punch card reader, printer, and FORTRAN compiler, was funded through a UK Overseas Development Agency (ODA) grant of £11,000, enabling students to gain hands-on experience with advanced computing tools.

HP 9825A Computer, the device was marketed as a calculator, but far more advanced than its competitors at the time (courtesy researchgate.net)

The HP 9625A played a pivotal role in my education between 1975 and 1979, offering invaluable hands-on experience in programming and computing during a formative era. Working with such cutting-edge equipment—at a time when computing was still emerging from its infancy—was nothing short of exhilarating. Guided by esteemed educators, I honed my skills in logic, structure, and problem-solving, laying the foundation for a lifelong engagement with technology. More than just a learning tool, the HP 9625A became a symbol of discovery and possibility, etching lasting memories into the fabric of my academic and computing journey.

“The HP 9825A was brilliant—but brilliance without support is just a flicker in the dark.”

The HP 9625A offered a comprehensive environment for learning programming. Not only did it come equipped with a FORTRAN compiler, but it also featured a punch card reader and printer. Together, these components provided an interactive and immersive experience that went beyond simple calculations, ushering in a new era of computer-assisted education. This hands-on approach to computing significantly boosted both my practical programming skills and my broader understanding of computer science fundamentals.

Built-in Thermal Printer

From a technical standpoint, the HP 9825A boasted several pioneering features for its time. It supported a two-level priority interrupt system and featured a live keyboard that allowed real-time examination and modification of program variables. With its direct memory access (capable of input speeds up to 400,000 16-bit words per second) and a high-performance bidirectional tape drive, the machine presented the user with an array of sophisticated data handling and processing capabilities. Additionally, it supported multidimensional arrays, automatic memory record and load functions, and an extended calculation range (from ±10^5 to 10^-11). Some of these features were part of its standard configuration, while others could be added through optional plug-in ROMs.

A particularly innovative aspect was the keyboard design. It came with twelve special function keys which, when combined with a shift key, could execute 24 distinct operations. This design was not only ideal for program development but also served as an interface for controlling peripherals and instruments. The keys were versatile—capable of executing immediate commands, calling subroutines, and even acting as aids for data entry. Furthermore, the live keyboard allowed users to inspect, edit, and run programs simultaneously, a revolutionary feature at the time.

The 32-character single-line display of the HP 9825A was custom-built for what would later evolve into the 9825A Calculator series. Each character on the display was defined within a 5-by-7 dot matrix, where every digit achieved a maximum height of 0.37 cm. The characters were formed using red light-emitting diodes, fabricated on a monolithic substrate, with four characters packaged together in a dual-in-line module. This innovative design was a significant leap in display technology, providing clarity and functionality in a compact form factor.

Another noteworthy feature was the integrated tape cartridge system, boasting a storage capacity of 250,000 bytes and a data transfer rate of 2,750 bytes per second. This configuration facilitated efficient data storage and retrieval, significantly improving the device’s throughput. The ample capacity supported rapid loading and recording operations, making the tape drive a critical component for users requiring dependable and high-speed data handling in time-sensitive environments.

Reflecting on my experiences with the HP 9825A, I remain grateful for the opportunity to work with such pioneering technology. It wasn’t merely a calculator but a comprehensive computing environment that laid the foundation for many of the modern computing principles we now take for granted. The hands-on encounters, coupled with the mentorship of remarkable educators, left an indelible mark on my academic journey and continue to influence my technical approach even today.

Hewlett-Packard Journal Cover Picture Courtesy of HP