【NEC】 IR-807 and IR-809 Magnetic Drum Units

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.

Specifications of IR-807 and IR-809 Magnetic Drum Units
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

IR-807 Magnetic DrumIR-809 Magnetic Drum<small>With front cover removed</small>