Final answer:
SMS restricts text messages to 160 alphanumeric characters, based on the original design of the SMS standard which uses 140 bytes of data per message.
Step-by-step explanation:
SMS, which stands for Short Message Service, technically restricts the length of text messages to 160 alphanumeric characters. This limit is due to the original design of the SMS standard, which allocated 140 bytes of data per message. Given that standard GSM encoding uses 7 bits per character, this allows for 160 characters (140 bytes * 8 bits/byte) / 7 bits/character).