Decoding part numbers

What does something like MSP430F1121 mean?

The letter indicates the type of ROM on board:

Note that only the original 3xx series parts use UV-EPROM. Everything after that uses Flash ROM. Programming the EPROM parts is done over the JTAG port.

The first digit after the letter is the overall family: 1, 3 or 4. They are roughly in increasing order of capability, but there's a lot of range. Parts are generally upward-compatible within a family.

Basically, 1xx parts don't have an LCD controller, while all the 3xx parts do. Both families have models with ADCs; the 11x2 parts have a 10-bit ADC, while others have a 12-bit ADC. Some parts have hardware UARTS, although any of them can bit-bang it.

Initially, the 1xx parts were small 20- and 28-pin parts, and the 3xx parts were 56 or 64 pins. However, the 1xx parts have grown up and the 13x and higher packages come in 64-pin packages, while the 3xx parts range from a 48-pin 31xS subset to 100 pins.

The second digit is the device within a family. Again, generally higher numbers are more capable, but it varies a lot. As a general overview:

A fourth digit, if present, is a sub-version number. A '1121 is a '112 with a little bit extra (an analog comparator for software ADC). A '1122 is a '112 with a 10-bit ADC. (Exception: the 161x parts.)

The third digit encodes the amount of memory on the chip:

The 16x series adds:

Note the 161x numbers are an exception to the usual 4th digit rule.