Unoke Electronic Industries (the company name was changed to USAC Electronic Industrial in 1969 and later to PFU) completed the development of the USAC 5010 and USAC 3010 in 1961. These were ultra-small computers designed to cover applications of computers that were later to be known as the office computer category. Although there was no clear concept at the time of an operating system, the computers were prepared with basic software and a number of functions intended to make the computers easier to use that found their way into later office computers.
- Stored program method
- Machine language with symbolic instructions
- Individual application programs could be run and used
- Came with an all-purpose I/O device called a Flexowriter: this device could boot, execute, and suspend programs
- Came with hardware-based CPU monitoring and control functions on the console panel
Unoke Electronic Industries extended its line up with the USAC 1010, the USAC 1020, and the USAC 500 to USAC 1500, which were distinctive for being designed specifically as billing machines (i.e., computers that made bills and other electronic forms). The renamed company then developed the USAC 720 series of ultra-small computers, all sharing a common architecture. The first model in the series, the USAC 720/10, was completed in September 1971. The USAC 720 series had the following five systemized processing models, which included software, in consideration of office computer applications.
- （1）Direct data processing system (DDPS): introduced billing functions to ultra-small machines
- （2）Magnetic ledger system: a function that processes magnetic ledgers
- （3）Multi-billing system: simultaneously processes different types of forms
- （4）Online terminal system: collects and transmits data
- （5）Batch system: processes batch data
Although the basic software did not have a name, the basic software provided the following functions, including a programming language for billing processes, in addition to functions equivalent to an operating system.
- Program load function
- I/O control system of subroutines that controlled I/O and edited data
- Assembly language
- Symbolic information management program language (SIMPL), a simple programming language for billing processes; later billing-oriented language (BOL) was added
- System utilities
- Service utilities (sort, merge, file maintenance)
These inherently office computer concepts and functions were used in the SPIRAL technology for the FACOM 230-15 and later in the FACOM V series and the FACOM Bm (USAC 820), which were jointly developed by USAC Electronic Industrial, Uchida Yoko, and Fujitsu.