"Hobby", a Z80 Computer Prototype compatible with CP/M & Sinclair ZX Spectrum Operating Systems

I started this project when I was 18, back in 1987, and developed it for a few years.

Hypertext (HTML) and WWW were not invented yet, so all the schematics (hardware) were designed starting from a few (paper) books and some datasheets. I was living in Bucharest, Romania, under the communist dictator Ceausescu. In 1987 Berlin Wall was still in place so Integrated Circuits (IC's) produced in western countries were not available in shops. Even IC's fabricated in Romania or Russia were not available in shops so i bought almost every piece of hardware from the black market.

The PCB was an universal test board. Soldered wrapping wire, not wrapped, was used for all the electrical connections.
To be able to run CP/M applications I wrote a CP/M BIOS using Z80 assembler.

At that moment in time the "Hobby" computer was cut of the edge technology:
- compatible with both of the major Z80 operating systems of the time: CP/M and ZX Spectrum
- single (256 x 192) and double (512 x 192) screen resolution
- hardware switched Z80 clock 3.5 MHz (standard) or 7 MHz (double)
- software memory pagination: Z80 can address maximum 64 KB of memory but this system had a total of 114 KB (64 + 16 KB of RAM and 32 + 2 KB of EPROM)
- first overclock that i knew so far (at that moment the maximum clock frequency for a Z80 microprocessor was 6 MHz, mine was working at 7 MHz)
- first "overburn" on floppy disks that i knew so far (similar with CD overburn but on floppy disks): the standard file system had normally 80 tracks on a floppy, mine had up to 85 tracks

22 years later i found the "Hobby" prototype full of dust and give it a try.

Guess what, it still working!
:)

A BIG "THANK YOU" TO ALL THE PEOPLE THAT HELPED ME TO DESIGN AND IMPLEMENT THE HOBBY COMPUTER PROTOTYPE

Filmed in HDTV with Nikon D90 and 18-105mm f/3.5-5.6G ED AF-S VR DX Nikkor Zoom Lens on 18'th of February 2009

Category:

Science & Technology

Tags:

• Hobby
• Z80
• CP/M
• Sinclai
• ZX
• Spectrum
• nostalgia
• computer
• overclock
• overburn
• hystory
• Nikon
• D90

[mentalthink]

this is awesome, thanks for the video, this is a grat beast.

A question, where you found information, books or another format, for can make a 8 bits computer.

Thanks,

[RoGeorgeRoGeorge]

@mentalthink

From written books, databooks, the sources from a Spectrum EEPROM and a CP/M listing with source codes.

[timecircuitsbuilder]

You made a fantastic work !!! I have the same project but I don't know how to find the operating system for my project. Where did you find your OS CP/M ? Thanks.

[RoGeorgeRoGeorge]

Merci beaucoup. J'ai vu votre laboratoire et je suis enchante de votre time circuits aussi!

CP/M is made by 3 components called CCP, BDOS and BIOS. To adapt CP/M to my computer I made a copy of the OS from the Felix M118 computer then stripped away the BIOS and completly rewrite it in Z80 assembler. This takes me A LOT of time. Later I found the source codes for the whole CP/M and i think i still have them somewere on the old 5'' floppy disks.

[zxspectrum128]

I admire what was done by you and others in countries where the Spectrum wasn't available. It's a shame that the last Spectrum users from those countries don't become more active in places like WOS, and don't try to have their work translated to English.

How compatible with the Spectrum was this computer of yours?

[RoGeorgeRoGeorge]

Thank you for your appreciation. It might be some uncompatible programs out there but i don't remember any game or utility that works on Sinclair ZX Spectrum and doesn't work on Hobby. If you know any program that usually works only on the original ZX Spectrum please let me know and i'll give it a try becouse i am curious to see the results too.

[erwin8971]

Dude fucking awesome

[VladMaster99]

z80...2114 Ram..2764 Eprom 4116 Dynamic Rams.

Added 41256 Rams and bankswitching later.

had also a 6809P as well

[richardmaudsley77]

how could you say this was cutting edge in 1987?

The amiga, atari st, Acorn archemedes, etc... Your computer is more like 1977 tech.

But it's cool though. CP/M is awesome.

[lordtapdoles]

This is REALLY, REALLY amazing. Well done! Especially aged 18 in 1987, without proper access to ICs - absolutely amazing.

[VintageJunior]

I didn't know the Speccy's OS worked on other Z80s.

[anticioroi]

Stima, respect si consideratie!!

[lich0x2b]

Maestre, tot respectul!

[nuclearthelab]

Awesome :) A friend of mine that came from the soviet union had a 48k spectrum clone back then, and we used to write spectrum programs together (I had the original 128k +2). I remember that machine of his being really ugly, but it worked flawlessly :)

It's good to find someone who actually created those beasts :)