Microarchitecture
The NVAX is partitioned into the five semi-autonomous units, the I-box, E-box, F-box, M-box and C-box. The NVAX is macropipelined. Multiple VAX macroinstructions are processed in parallel by autonomous units, which have their own micropipelines.
The I-box fetches and decodes VAX instructions. It also contains the 2 KB direct-mapped virtual instruction cache (VIC) and the 512-entry by 4-bit branch history table. The I-box aimed to fetch eight bytes of instruction data from the VIC during every cycle.
The E-box executes most non-floating-point instructions. It is controlled by microcode from a 1,600-word control store with the capability to patch 20 words.
The F-box executes floating-point instructions as well as 32-bit integer multiply instructions. It has a four-stage floating-point and integer multiply pipeline and a non-pipelined floating-point divider.
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