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.
|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|
|Weight (kg)||Approx. 100||Approx. 10|