These defcon slides give a good overview of one

Atmel AT90SC25672RU, 8-bit AVR, 256KB ROM, 72 KB EEPROM, 6 KB RAM, Between 20 & 30 MHz

https://media.defcon.org/DEF%20CON%2021/DEF%20CON%2021%20pre...

That's one example, but they are usually an 8-bit architecture with special tamper-resistance features, similar to what's found on payment cards.

So next question, is a credit card chip also a computer?

Yes, a very limited one but you can put a bunch of interesting things there, the EMV standard documents how other apps should be put there so that the customer can have a card that works both as a credit card in CC terminals and also have additional features that are accessible either in specialized terminals or custom CC terminals with explicit support enabled e.g. some loyalty card or discount scheme.

Here's a list (IMHO not exhaustive) of some apps put on EMV cards https://www.eftlab.com/knowledge-base/211-emv-aid-rid-pix/ - there are various identity card solutions both from governments and companies like Microsoft, there's https://en.wikipedia.org/wiki/OpenPGP_card , there's various solutions for store loyalty cards.

However, I don't consider this aspect as any risk to the user, since when using the standard payment card functionality your card payments already have no privacy or security whatsoever from the issuer of your card, from a technical perspective the issuer will (by design) see and manage (authorize, revoke, etc) all the transactions and the card + terminal is just one of the channels for sending cardholder-initiated transactions to them. It would be technically appropriate to treat it not as "your card" but "issuer's card" that the cardholder uses as a token to use when the merchant communicates with the issuer about the bill.

A good rule of thumb is that nothing is just memory wothout a processor. Including stuff that is sold as jyst memory (eg SD cards).

Yeah, most of this applies there too.

That‘s definitely still true for many existing cards, but newer ones are switching to ARM-M based architectures, as far as I know.

My SIM card has 30x more horsepower than my C64. Mind blown.

Thats a joke..

Also applies to other SmartCards, they sometimes even run Java applets

https://www.researchgate.net/figure/The-basic-architecture-o...