Mike's PCjr Page

I managed to snag this oddity off of eBay for super cheap, so I'm looking forward to playing with it. For you gents who have had experience with cassette loading:

- I'm assuming the best I'll be able to do with this is save/load BASIC programs? After all, it's Disk Operating System, not Cassette Operating System, right?

- I'm assuming that this is a bitstream similar to an analog modem transfer? What's the "effective baud rate" you get from cassette load?

- How much data can I fit on a cassette? Is it limited only to the length of the tape (could I do close to 64k)?

- I'll probably get a cassette unit and a couple blank cassettes just to have some fun, but is it also feasible to just go straight audio cable to an iPod mini or something, and play back the audio files from there to load them into the PCjr memory?

Have you seen this?

http://www.brutman.com/Cassette_Wavefor ... forms.html

In theory you can save and load arbitrary data to the cassette; there is a BIOS routine that gets called to write blocks of data. So it's not just for BASIC programs, but you have to use some BIOS calls directly to do that.

The bit rate varies depending on whether you are writing a 1 or a 0 bit. A 1 bit takes longer at 1 full millisecond to write. So if your data was all ones you could write at 1000 bits per second, or 125 bytes per second (ignoring the initial header.) Zeros write at 2000 bits per second, or 250 bytes per second. Assume an average of 187.5 bytes per second and that gives you 660KB on a tape if you could do it in one pass. If you could write only zeros you could do better.

If you were slightly crazy you could do TCP/IP over the cassette interface. The start of each packet alone would take 256 milliseconds because that is what the BIOS takes to write the header. After that would be your data; a short packet (64 bytes or 512 bits) would take about 300 ms, plus an extra 256 for the BIOS imposed header, or about 0.6 seconds with some rounding error. A full length packet (1500 bytes) would be 8.25 seconds. To give you an idea how bad this would be, if you were using telnet to a BBS that would be a full second of round trip time to send and receive a single byte back. ;-0

Great read, thanks. I wonder if any cassette programs even exist out there that are PCjr-specific.

You know what's funny ... since it's just an arbitrary audio-based bit-stream, couldn't you even use a VCR and VHS tapes as high-capacity storage media? I remember recording Dolby Surround music onto VHS tape once from my Playstation and it was low-noise, high-quality audio.

Insanity!

I would think that the cassette adapter would have primarily been intended for the rare 64k, no floppy configuration to allow users to save BASIC programs. I haven't yet seen anything for the PCjr that was commercially released on cassette so if you have a floppy drive, you're set to run virtually anything that was released commercially and have a faster and more reliable medium for saving your own programs. Everything I have seen so far has been on cartridge or floppy. Where I would check is in the review section or classified ads of old computer magazines to see if anyone released anything on cassette. There were a lot of independent programmers that would sell direct via magazine ads back in the day so if anyone did release anything on cassette, that would be the place to look. You'd still have to hunt down a copy because the ads would be expired, but at least you'd know if anything was released on tape.