From Halopedia, the Halo wiki
Cryo B was a cryogenic stasis chamber on board the Halcyon-class light cruiser UNSC Pillar of Autumn. Cryo B had two sections, separated by two corridors at the bottom, and the main terminal at the top. Each section held 28 cryo-tubes.
John-117 and Linda-058 were placed here during the trip from Reach to Installation 04. Following standard UNSC procedure, Keyes jettisoned most of the cryo-tubes upon arrival in-system and there were only nine of them left when they found Installation 04. The first side is where John awoke and tested his armor shields, whereas is likely the other side was used for the "weapons diagnostics" mentioned in the beginning of Pillar of Autumn.
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