The odd one out in this list is option D: HP2100 series.
Explanation:
TI990:
- TI990 is a series of minicomputers developed by Texas Instruments.
- It was introduced in the 1970s and was used in various applications such as scientific research, industrial control systems, and data processing.
- It was known for its advanced architecture and high-performance capabilities.
PDP-8:
- PDP-8 is a series of minicomputers developed by Digital Equipment Corporation (DEC).
- It was one of the first commercially successful minicomputers and was introduced in the 1960s.
- PDP-8 was widely used in scientific, industrial, and educational applications.
IBM704:
- IBM704 is an early mainframe computer developed by IBM.
- It was introduced in the late 1950s and was used for scientific and engineering calculations.
- IBM704 was known for its floating-point arithmetic capabilities and was used in various research institutions and universities.
HP2100 series:
- HP2100 series is a series of minicomputers developed by Hewlett-Packard (HP).
- It was introduced in the late 1960s and was widely used in industrial and scientific applications.
- HP2100 series was known for its reliability and flexibility.
Conclusion:
The odd one out in this list is option D: HP2100 series. This is because the other three options (TI990, PDP-8, and IBM704) are all minicomputers, while HP2100 series is a minicomputer series.