Archive for the ‘Uncategorized’ Category

Comparison of CGA card versions

Monday, October 8th, 2012

Over at the Vintage Computer Forums I asked about the differences between CGA card versions.

The main change that occurred during the CGA's lifetime seems to be to do with composite output. In particular, the old CGA (part numbers 1804472 and 1501486) had the following formula for the composite output voltage: COMPOSITE = 0.72*CHROMA + 0.28*I. The new CGA (part numbers 1504910 and 1501981) has the formula COMPOSITE = 0.29*CHROMA + 0.1*R + 0.22*G + 0.07*B + 0.32*I. The consequences of this are more obvious on a monochrome monitor, since there CHROMA only makes 3 different shades of grey (0 for colours 0 and 8, 1 for colours 7 and 15 and 0.5 for all the others). So an old CGA will only yield 6 different shades of grey on a monochrome monitor, while on a new CGA the 16 different colours will yield 16 (theoretically) different shades of grey (though some of them may be very similar).

On a colour monitor, a new CGA will give a lower saturation then an old CGA, but the brightnesses of the different colours will seem more appropriate. On an old CGA, blue seems lighter than it should be while yellow seems darker - new CGA fixes that.

The other thing about new CGA is that its composite output is a better match to standard NTSC than old CGA's, which means that the results will be more consistent between different monitors. The old CGA's color burst has both too high of an amplitude and too high of a DC offset, which causes many NTSC output devices to reduce the gain, making the resulting image too dark (I have to turn the brightness and contrast right up to get a decent image from my 1501486 card on the TV I connect it to).

That's the theory - to check how well it works in practice, I'd like to do some side-by-side comparisons. Rather than trying to buy a new CGA card (which is likely to be expensive, might be unsuccessful and probably wouldn't work too well side-by-side with another CGA card in the same machine anyway), I want to make an add-on card for my old CGA card which adds a second composite output, with new-style colours. The differences between the two cards are localized to a small part of the circuit, so there isn't too much to duplicate.

The future of the past and the past of the future

Sunday, September 23rd, 2012

Today is the 50th anniversary of the first broadcast of the Jetsons. It's always fascinating to look at how the people in the past used to imagine the future would be like, and see how different their extrapolations were to how things actually turned out. There are certainly technologies and societal changes that have happened in the last 50 years that would have been impossible to predict.

Equally fascinating, I think, is to imagine how people in the future will think of our present. Okay, it's a rather different problem in that there will (hopefully!) be actual historical records of what life today is like (in fact, our present is probably the most well-documented historical period ever). Still, we surely have misconceptions today about what life was like in the past, and it's interesting to wonder what misconceptions the people of the future will have about us. What technologies that have yet to be invented will be so ubiquitous and game-changing that people will have real trouble imagining what life was like without them? What changes will happen to society which will make today seem unfathomably alien? Given enough time, I'm sure such changes are inevitable, so (despite the excellent records) I think it would be completely unsurprising if the people of tomorrow have some serious misconceptions about the people of today (especially amongst those who don't study the past for a living).

Credit card designed for internet shopping

Friday, July 23rd, 2010

It seems like it would be possible to make a great deal of money by creating a payment system better than credit cards. Paypal has come closest to doing this, but has a lot of problems.

How could one make credit cards better? It would be very difficult to get your payment system into as many retailers as Visa and Mastercard, so perhaps aiming for a niche would be a good idea. One such niche might be internet purchases. Develop a payment system/credit card designed specifically for internet purchases and it could be very popular.

One major difference between a payment system designed for the internet and one predating it is that one could authenticate the transaction, not the identity. Whenever you buy something online, you put in your card number as usual but then (unlike with normal credit cards) there is an extra step - you log into the payment system's website and approve the requested transaction. Until you have done that, the merchant doesn't get any money (and won't deliver the goods). This cuts out all "stolen card" type fraud, since the thief would also need to steal your payment system password (which never goes anywhere near the merchant). This would allow this payment system to undercut the existing credit card issuers and become competitive. Fraud caused by loss of the payment system password would be treated the same as fraud caused by the loss of any other online banking password (which I think varies from place to place).

This system would still need a "chargeback" mechanism to combat fraud from merchants (and mechanisms to combat fraudulent chargebacks) but my impression is that the costs of these are small compared to the "stolen card" costs.

With suitable cellphone applications for authorization, the system could even be used for brick-and-mortar stores as well.

Unlike Paypal, this system would actually be able to lend money like a credit card, it wouldn't need to be linked to a bank account or credit card.