The SC-3000 was the computer equivalent of the SG-1000.
The SC-3000 sold for ¥29,800 (USD$386.81) in 1983 and was marketed as a computer for beginners. Since games were compatible with both the SC-3000 and SG-1000, and since the SC-3000 was also able to run computer applications, it outsold the SG-1000.
Users were able to create their own programs and games on the machine in BASIC, as well as machine code. A speech synthesis unit, light pen, and several other third party accessories were also available.
Source: Wikipedia, "Sega SG-1000", available under the CC-BY-SA License.