In March 1961, NEC completed the No. 1 prototype of the IR-807 and IR-809 magnetic drum units for use as internal memory of the NEAC-2205 and NEAC-1201 small computers. They were exhibited and operated at the Tokyo International Trade Show in April of that same year.
These were compact and easy-to-maintain devices for use with small computers, and were designed with resistance to temperature, humidity and dust for use in ordinary office environments.
In the NEAC-2205, the IR-807 stored 100 words in 1 track cycle (1 word in the NEAC-2205 was comprised of 44 bits), and a total main memory capacity of 3000 words was achieved by using 30 tracks for main memory. In addition to the ordinary tracks for main memory, the unit was provided with 3 tracks of temporary memory (20 words) and 2 tracks of temporary memory (10 words) as loop memory, and 1 track as a loop register.
For this loop memory and loop register, two magnetic heads were arrayed at a fixed spacing on a single track, and a sort of delay line memory was configured by dedicating one head each to reading and writing, and sending read output to the write circuit via computer circuits.
| Model name | IR-807 | IR-809 |
|---|---|---|
| Drum dimensions(mm) | 290ø×110 | 100ø×55 |
| Rotation speed(rpm, at AC60Hz) | 2500 | 1750 |
| Average access time(msec AC60Hz) | 12 | 17.1 |
| Number of information tracks | 30 | 20 |
| Memory capacity in 1 cycle (bit) | Approx. 5,000(NRZ) | Approx. 800(RZ) |
| Total memory capacity(bit) | Approx. 150,000 | Approx. 16,000 |
| Use conditions Temperature(°C) | 5-35 | 5-35 |
| Permissible temperature variation(°C/hour) | 6 | 6 |
| External dimensions(mm) | Approx.660×500×500(H) | Approx.210×300×235(H) |
| Weight (kg) | Approx. 100 | Approx. 10 |
| Applications | NEAC-2205 | NEAC-1201 |
