This article presents a scalable parallel ultrafast optical random bit generation method based on a single chaotic microcomb. Random bit generators are essential for information security, cryptography, and simulations. Current physical random bit generation faces challenges in speed and scalability. The proposed method uses a single micro-ring resonator to generate ultrafast random bit streams at rates up to 100 terabits per second. A modulation-instability-driven chaotic comb in a micro-ring resonator enables the simultaneous generation of hundreds of independent and unbiased random bit streams. A proof-of-concept experiment demonstrates that using this method, random bit streams beyond 2 terabits per second can be generated with only 7 comb lines. This bit rate can be easily enhanced by increasing the number of comb lines used. The method provides a chip-scale solution for secure communication and high-performance computation, offering superhigh speed and large scalability. The chaotic microcomb is produced using a CMOS-compatible, high-index, doped silica-glass micro-ring resonator. By selecting comb lines in designated areas, parallel chaotic waveforms with symmetric distribution and no correlation can be obtained. The detected chaotic waveforms are oversampled by their respective 16-bit ADCs and directly quantized into unbiased random bit streams by retaining 8 least significant bits. A proof-of-principle experiment demonstrates that using this method, an ultrafast parallel physical random bit generator with a single chaotic microcomb can reach a 320 Gb/s generation rate in each channel, and a total bit rate of 2.24 terabits per second can be obtained by using 7 channels. The method is amenable to chip-scale parallel random bit generation due to its ultra-small size and simplified random bit extraction. The generated random bit streams are verified to be statistically independent and have high-quality randomness, passing all NIST tests. The method offers a promising integrated physical entropy source for ultrafast physical random bit generation.This article presents a scalable parallel ultrafast optical random bit generation method based on a single chaotic microcomb. Random bit generators are essential for information security, cryptography, and simulations. Current physical random bit generation faces challenges in speed and scalability. The proposed method uses a single micro-ring resonator to generate ultrafast random bit streams at rates up to 100 terabits per second. A modulation-instability-driven chaotic comb in a micro-ring resonator enables the simultaneous generation of hundreds of independent and unbiased random bit streams. A proof-of-concept experiment demonstrates that using this method, random bit streams beyond 2 terabits per second can be generated with only 7 comb lines. This bit rate can be easily enhanced by increasing the number of comb lines used. The method provides a chip-scale solution for secure communication and high-performance computation, offering superhigh speed and large scalability. The chaotic microcomb is produced using a CMOS-compatible, high-index, doped silica-glass micro-ring resonator. By selecting comb lines in designated areas, parallel chaotic waveforms with symmetric distribution and no correlation can be obtained. The detected chaotic waveforms are oversampled by their respective 16-bit ADCs and directly quantized into unbiased random bit streams by retaining 8 least significant bits. A proof-of-principle experiment demonstrates that using this method, an ultrafast parallel physical random bit generator with a single chaotic microcomb can reach a 320 Gb/s generation rate in each channel, and a total bit rate of 2.24 terabits per second can be obtained by using 7 channels. The method is amenable to chip-scale parallel random bit generation due to its ultra-small size and simplified random bit extraction. The generated random bit streams are verified to be statistically independent and have high-quality randomness, passing all NIST tests. The method offers a promising integrated physical entropy source for ultrafast physical random bit generation.