The UNIVAC 90/60 was a complex instruction-set computer (CISC) primarily designed for problem-state instruction-set compatibility with the IBM 360 series of mainframe computers. The CPU was microcoded and could also emulate the instruction set of other machines, including the IBM 1401, and many of the RCA computer systems that preceded the RCA Spectra Series (from which the UNIVAC 90/60 evolved.)
In general terms, the UNIVAC 90/60 was a 32-bit machine with 16 general-purpose 32-bit registers and a 64-bit program-status-word (PSW). The CPU implemented a "scratchpad" of fast memory, multiple register sets for fast context-switching (4-sets for a total of 64 registers), semiconductor RAM (as opposed to core or thin-film memory), and a virtual-memory system with page-swapping to disk.
Storage was organized along multiples of 8-bit bytes, with the byte serving as the basic unit of addressable storage. Various instructions operate on larger units called halfword (2 bytes), fullword (4 bytes), doubleword (8 bytes), quad word (16 bytes) and 2048 byte storage block, specifying the leftmost (lowest address) of the unit. Within a halfword, fullword, doubleword or quadword, low numbered bytes are more significant than high numbered bytes; this is sometimes referred to as big-endian. Many uses for these units require aligning them on the corresponding boundaries.