Kermit Setup and CP/M

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Don’t expect fancy setup utilities in CP/M. This is the process to create a machine compatible version of Kermit (terminal emulator software). MLOAD.COM takes the main program file in HEX and modifies it using the machine specific HEX file. The result is an executable file (COM) of the desired program.

Although there were text-based DOS programs around even in the 90s, their interface was usually far more user friendly with all the setup utilities, pull-down menus and other cool features. CP/M and early DOS programs were a perfect example of how simple and crude the software from the early- and mid- 80s was.

Kermit also reminds me a big advantage of the “PC compatibility”. In theory, the CP/M software was universal. However, different floppy formats, different pinouts on serial/parallel ports and different screen handling commands made life much tougher for both software developers and users.

CP/M and Input/Output Redirection

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It is nice about CP/M how easily the input from a keyboard and output to a CRT can be redirected to another computer over a serial port using a single command.

SAPI-1 (1983)

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On the left side, you can see SAPI-1 – a professional computer that was made in the Czechoslovak Socialist Republic and was used mainly for industrial applications. Its architecture was modular and not very far from S100-bus computers. One of the cards contained CPU (Zilog Z80 in this case) while other cards contained RAM, ROM and communication interfaces. It was able to run CP/M which was loaded from 8-inch floppy drives.

This photo is from the last Bytefest show a few weeks ago. We were copying files over a null-modem cable from Amstrad CPC6128. File transfers between different CP/M computers were not an easy task back in the 80s. Each computer had different floppy drives or at least a different logical format of the disks. This was very similar to terminal incompatibilities where every full-screen program had to support tens of terminals in order to be compatible with most CP/M computers. If your computer was not on the list, you ended up with incorrect layout of the text on the screen.

Because of these incompatibilities, serial and modem connections were the best ways to transfer files back then and they are even today. Don’t expect something “plug and play”. Although I could set the transfer speed in software on Amstrad CPC6128, the owner of the SAPI-1 had to remove the communication card and change the serial link configuration using a soldering gun. Another issue was to find programs with compatible transfer protocols but that’s a different story. Finally, after less than an hour, we were able to copy all our precious files.

Amstrad (Schneider) CPC 6128

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Although Amstrad CPC is not the preferred choice among vintage computer fans, it’s definitely a very interesting series of 8-bit computers and was sold in millions of units. This model combines 80-column display (screen resolution of 640×200), integrated 3-inch disk drive (each diskette can hold 360kB of data), AY sound and surprisingly good keyboard.

 This was one of the cheapest computers that could run CP/M, the operating system with many professional programs available. Although Wikipedia says that there were a lot of games on CPC computers, I saw only people using this machine for actual work. This particular machine was used in the late 80s by a scientist in a geophysical institute for simulations and word processing. He sold the machine with an 5.25-inch external drive (made by Robotron and modified to work with CPC), an RS232c interface and a box full of disks containing development tools, his own Pascal programs and a customized version of WordStar (that allowed users to write and read Czech characters).

 The keyboard is better that those on 8-bit Atari and Commodore computers and the computer gives more professional overall feeling. I like how CP/M has been integrated in the system. You can easily switch between BASIC (AMSDOS) and CP/M environments by using |CPM and AMSDOS commands and both use the same way to store files on disks.

 I know that it is possible to run CP/M also on Spectrum +3 and Commodore 128. However, the former supports only 40-column display and the latter is significantly slower due to hardware design limits. This was a better choice for those who wanted to use CP/M on a home computer back then.