The machine itself was made by Convergent Technologies. It's similar to the MiniFrame - and possibly also the MightyFrame.

AT&T rebranded it, and there were two versions: the 7300 can take a single half-height MFM drive, and the 3B1 can take two half-height MFM drives or a single full-height. The 3B1 has a different plastic case with a square-ish 'bump' under the monitor, and usually a modified (called a P5.1) motherboard.

They top out at 4MB RAM (2MB on the motherboard and 2MB on expansion cards). Disk storage would have topped out at 190MB with a single Maxtor XT-2190 full-height, or a pair of Miniscribe 3650s for 2x50 = 100MB.