using new technology on old machines. Was: PDP-12 Restoration at the RICM

Mark J. Blair nf6x at
Mon Jun 15 17:06:41 CDT 2015

> On Jun 15, 2015, at 14:56 , Dave G4UGM <dave.g4ugm at> wrote:
> A friend of mine refused to buy modern SD Cards because there was no way he
> was going to fill them. Trouble is that although smaller SD cards were
> available they were way more expensive (being discontinued and therefore
> rare and valuable).. He struggled with buying a larger card only to waste
> most of it, or buy a smaller one and waste his money....

I had that same mental hangup when thinking about how I might design an SD card based TU58 emulator in the same form factor as a TU58 cartridge (still on my to-do list, by the way). How was I going to implement the user interface? It's not like there's much room for an LCD or buttons on the edge of a TU58 cartridge. Then it finally hit me: SD cards are cheaper than TU58 cartridges ever were. So why not just use the first 256k, ignore the rest of the card, and swap cards exactly the way one would swap TU58 cartridges, with one image on each card? Yeah, 99% of the card is "wasted", but they're presently cheap and plentiful enough to ignore that.

Ok, I might actually have the emulator read a file from a DOS filesystem rather than using the first 256k of raw blocks. But it'll probably just be a fixed filename with no controls to select a different one, and the expectation that an entire (cheap, plentiful) SD card will be devoted to each tape image. At least this way, other things can also be on the card, so it doesn't need to be wasted if not needed.

Your friend should understand that the larger card that he would be "wasting" probably has less silicon in it than the older one with less capacity. The cheapest card that is reliable, fast enough and large enough for his task is the best one to get, even if it's much larger than he needs. Just one of the weird parts of the Moore's Law curve!

Hmm, this reminds me that back in the day, floppy disks were expensive. We have it easy with cheap and plentiful SD cards nowadays. But maybe my perspective is different as an employed adult rather than a teenager with limited funds? Anyway, SD cards seem to be cheap enough to be nearly disposable nowadays.

Mark J. Blair, NF6X <nf6x at>

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