Hewlett-Packard HP85

What a nice desktop computer ! Hewlett-Packard reputation for making the finest equipment reached the top with HP85. As they thought to penetrate the market with a professional desktop computer they invented the HP85.

The project started in the late '70s and the HP85 appeared on the market in 1980. I read some fascinating articles on the HP Journal about the design challenges that were faced and the engineering solutions that were adopted.

As stated for the Tektronix 4051, the characteristics of the HP85 might appear very poor compared to nowadays PCs. But a modern PC is still not as professional as the HP85 was at the beginning of the '80s.

These were the HP85 characteristics:

  • 8 bit CPU at 1 (one!) MHz clock
  • 16 kB RAM expandable to 32
  • ROM operating system and ROM HP-BASIC
  • built in 5" b&w graphics screen
  • built in 5" thermal paper printer
  • built in 128 kB digital cartridge mass storage unit
  • four expansion slots
Expansion slots could accomodate the following options:
  • 16 kB additional RAM
  • 32 kB additional ROM (6 elements of 8 kB ROM each)
  • a system monitor
  • RS 232 serial interface
  • GP-IB parallel interface (called HP-IB)
The additional ROM added (to the yet powerful built-in language) the capabilities to manage printer, plotters, I/O interfaces, and even assembly programming. The system monitor was needed to provide breakpoints facility when debugging assembly programs.

The serial and the parallel standard interfaces permitted the HP85 to connect to any peripheral the programmer could have ever thinked of: not only printers and plotters, but a whole world of measuring instruments and Data Acquisition & Control units.

I bought my HP85 on 1981, february. I payed six months of my salary for that unit, and I still keep it although I can't use it anymore because the rubber of the digital cartridge drive wheel for some strange reason melted.

I quickly learnt the HP BASIC and wrote the following programs:

  • a finite-element method structure solver
  • a mold cooling simulation to determine the optimal flow rate and the optimal temperature of the cooling water
  • a cam contour designer
  • an EPROM contents calculator
In 1983 I bought the assembly ROM and the system monitor, and started learning the HP85 assembly language. Dumping the memory I made my first hack: I discovered how to remove the software protection against program piracy. This protection inhibited to save a program on a digital cartridge different from the original it was loaded from. This way valuable programs could have been bought only from the original programmer.

Studying the assembly language I learnt a lot of interesting things about HP85. Its CPU was HP proprietary, and presented 64 registers 8 bit each. The CPU registers could be grouped togheter in different ways. For example the programmer could make up to 4 groups of 8 registers each. Each group could then be managed as if it were a single 64 bit register, and used to hold double precision floating point numbers. Then with a single call to a system routine the programmer could perform any math operation, no care about carry or overflow. Simply great.

The IBM PC appeared in Italy in 1982, with its ridiculous DOS 1.0, and resulted very poor compared to the professional performance of the HP85. It was simply impossible to write a program that could resemble a program written with the HP85.

But the PC was supported by IBM, the authority in the computer market, the DOS was patched little by little, people started using Visicalc (the former spreadsheet) and WordStar, and the PC/DOS gained popularity. You know the rest of the history...