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The 7090 used a 36-bit word length, with an address-space of 32K (32,768) words. It operated with a basic memory cycle of 2.18 μs, using core memory technology from the IBM 7030 (Stretch) project.
The basic instruction format was a 3-bit prefix, 15-bit decrement, 3-bit tag, and 15-bit address. The prefix field specified the class of instruction. The decrement field often contained an immediate operand to modify the results of the operation, or was used to further define the instruction type. The three bits of the tag specified three index registers, the contents of which were subtracted from the address to produce an effective address. The address field either contained an address or an immediate operand.