I’m very sorry about not seriously posting for a very long time.. Not that I haven’t made any stuff, but never found the time to write about it. To make it up with you I’ll start with two little projects which are a bit useless nowadays, but did intrigue me back in the 80s. Even now I’m amazed about how much people hacked modded their system in a simple but stunning and clever way. I highly doubt this kind of modding is even possible with the current gen of computers.

This little gem hides itself in the shell of a DB23 connector and basically detect (or prohibits) writes to track0. The first generation of viruses hid themself in the bootblock of the floppy. They spread themself by replacing the bootblock of other disks with their malicious payload. The basics of the detector part are very simple; the floppy bus has two signals we are interested in: /TRK0 and /WE. When something (i.e. a virus or XCopy) is writing to the bootsector both are low. To produce a beep or light a LED we need a high (1) output. To accomplish this the device uses a 74×02 (Quad 2 input NOR gate).

The protector part uses diode logic to pull the /WPROT line down when track 0 is accessed (/TRK0 low). It will totally block all writes to track 0 (and not just the bootblock which is located only in the first two sectors). This can cause troubles when writing files to the disk. The other option is to permanently pull /WPROT low to prevent any writing to the floppy.

Recently Rob Smith reviewed a similar unit on youtube and ‘discovered’ that if you try to write directly to the disk without honouring the write protect status, the write will succeed and the disk will still get infected. I kinda doubt this is a real issue as bootblock viruses are kind of simple due to the small codesize. I found two source codes of bootblock virus here and here and by looking at the code they both intercept DoIO() system calls to do their spreading. I’m not an expert in this but would guess we are on the safe side. Feel free to leave a comment on this below..

Another fascinating piece of hardware was the Video Backup System, originally by Hugo Lyppens. Back in the days I haven’t managed to replicate the PCB that was floating around in de warez scene (had no money to buy it back then). The interest was sparked again when I started to restore my old Amiga. The most clever part of this was all done in software with little help of the hardware. The data to the VCR was generated with the Amiga Custom chips. A data stream was generated and overlayed on the composite black white video signal to mimic a serial . A serial hardware decodes the black and white back into RS232 signals. From the advertised speeds i guess the baud rate is 14k4 or 19k2. Love to find out more technical details how he managed to read back serial, error correct it and write it back to floppy on a stock Amiga 500/2000.

I’ve got some spare PCB just in case if someone wants to be ‘protected’ against viruses or restore an old backup on ol’ VHS tapes, please drop an email to the info@{this domain}.

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