CP/M 80 in 2021?

Yes, what reason would there be to use CP/M in 2021? The reason could be, because...!

There can be a multitude of reasons why we might be tempted to discover something other than the boring soup we are served all day long, the digital world : in fact 'shits' for everyone, and huge profits for a few!

And why not take ownership of the tool and have it do something else? Obviously, you probably won't be able to use these simple systems for typing your new bestseller, listening to music, send the latest information of your exciting life to the whole earth or watching series. But there might be more things you can do that you can't do with your MAC or PC.

For that, a system must be simple and easy to use while being inexpensive. At the beginnings of the democratization of computing, in the early 80s, one of the flagship microprocessors was the Z80 in normal (2,5MHz) version or 'A' (4MHz) version and the dream version 'B' (6MHz). 

At that time, there was an operating system for this type of processor, the CP/M, called CP/M 80 when a version was developed for the first IBM PC and named CP/M 86, which later became the Microsoft DOS.

At the beginning of the 90s, I had recovered a CP/M 80 machine from a company which had switched to PC/DOS. Unfortunately, I no longer own this machine but this is what it looked like:

Wikipedia

Wikipedia

This type of equipment was sold for around $ 2,000 in the early 1980s, or something like $ 6,000 today. All that for 64K or 128K of RAM, a floppy drive of a few tens of Kbytes and a processor at 2MHz, possibly 4MHz : fantastic!

An operating system offers all the tools necessary to use a computer and, above all, allows a program to be loaded into RAM memory from storage memory and then to be executed, basically. 

The question is: is it still possible to get a CP/M version for Z80 and is it possible to adapt it to a preferably new machine with more capacities?

Good news, the answer is yes! More interesting, there is even a more general system which allows to launch CP/M but not only, and which is compatible with a certain number of systems based on Z80 or Z180 : the RomWBW from Wayne Warthen.

And so .... It only remains to find a hardware on which to implement this system. And precisely, while browsing the distribution of RomBWB I discovered the compatibility provided for a board named 'Easy Z80' designed by Sergey Kiselev :

https://github.com/skiselev/easy_z80

As this project is open source, I therefore made the printed circuit board in several copies and assembled one using components I own. My tests were carried out with a 4MHz oscillator because I do not have Zilog components certified at 10MHz (the CTC & SIO). 

I assumed this should still be fine because the SIO (UART) has its own clock independent of that of the processor. Obviously, if the operating system integrates calibration loops, the times provided will not be correct. But hey, for a first test this should not pose a problem ...

Indeed, it works :

So far I haven't pushed the tests any further. The characteristics of this system are very interesting. It is designed to operate at a frequency of 10MHz. Not even imaginable at the time. Has 512Kb of backed up SRAM of which 384Kb is reserved for drive A. Two serial ports are available as well as an RC2014 compatible expansion port. All for less than $ 100 when assembled.

As a first step, it is an ideal system to get acquainted with CP/M. The only small lack is the absence of inputs / outputs. But this can easily be offered later thanks to the extension port. In development mode it is necessary to connect this system to a terminal or a PC / MAC with terminal emulator. But simple and inexpensive solutions exist to allow the connection of a keyboard and a VGA screen. I intend to test this type of solution soon, which would make this system completely autonomous in the same way as the Color Maximite II.