Most PCs are inclined to boot from a first-rate media storage, be it a laborious disk force, or a solid-recount force, seemingly from a community, or – if all else fails – the USB stick or the boot DVD involves the rescue… Enjoyable, eh? Dull! Why don’t we strive to boot from a fable player for a metamorphosis?
So this nutty diminutive experiment connects a PC, or an IBM PC to be proper, straight away onto a fable player thru an amplifier. There is a dinky ROM boot loader that operates the built-in “cassette interface” of the PC (that used to be no longer regularly frail), invoked by the BIOS in case your whole assorted boot alternatives fail, i.e. floppy disk and the laborious force. The turntable spins an analog recording of a dinky bootable learn-handiest RAM force, which is 64K in size. This includes a FreeDOS kernel, modified by me to cram it into the memory constraint, a micro variant of COMMAND.COM and a patched model of INTERLNK, that lets in file switch thru a printer cable, modified to be runnable on FreeDOS. The bootloader reads the disk image from the audio recording thru the cassette modem, hundreds it to memory and boots the system on it. Straightforward huh?
And now to earn more technical: right here’s mainly a merge between BootLPT/86 and 5150CAXX, minus the printer port reinforce. It moreover resides in a ROM, in the BIOS growth socket, but it would no longer appreciate to. The connecting cable between the PC and the fable player amplifier is expounded to with 5150CAXX, precise with out the road-in (PC knowledge out) jack.
The “cassette interface” itself is precise PC speaker timer channel 2 for the output, and 8255A-5 PPI port C channel 4 (PC4, I/O port 62h bit 4) for the enter. BIOS INT 15h routines are frail for diagram (de)modulation.
The boot image is the same 64K BOOTDISK.IMG “instance” RAM force that could be downloaded on the bottom of the BootLPT article. This has been grew to become into an “IBM cassette tape”-protocol compliant audio stamp using 5150CAXX, and sent straight to a fable lowering lathe.
Vinyls are minimize with an RIAA equalization curve that a preamp in most cases reverses all the map in which thru playback, but no longer completely. So some stamp correction needed to be applied from the amplifier, as I couldn’t construct it work beautiful with the road output straight from the phono preamp. In my case, intriguing a vintage Harman&Kardon 6300 amplifier with an integrated MM phono preamp, I had to proceed the treble your whole map down to -10dB/10kHz, amplify bass equalization to approx. +6dB/50Hz and minimize the amount level to roughly 0.7 volts height, so it doesn’t distort. All this, naturally, with any portion and loudness correction grew to become off.
For sure, the cassette modem would no longer give a hoot in hell in regards to the place the stamp is coming from. However, the recording desires to be pristine and gain no pops or loud crackles (vinyl) or modulation/frequency tumble-outs (tape) that could wreck the knowledge circulate from continuing. Alternatively, some wow is tolerated, and the price could be 2 or 3 percent elevated or lower too.
And that’s it! For these , the bootloader binary designed for a 2364 chip (2764s could be frail, thru an adaptor), could be received right here. It assumes an IBM 5150 with a monochrome conceal and never lower than 512K of RAM, which more or much less rings a bell in my memory of my setup (what a twist of destiny). The boot disk image could be received on the bottom of the BootLPT/86 article, and right here’s its analog variant, straight from the grooves 🙂