1953: diode plug-in unit and the IBM 650
IBM 650
The IBM 650 had a magnetic drum memory and thus replaced the expansive storage tube, which served as secure programs and data. This consisted of a 35cm-long, cobalt- nickel- coated drum with a diameter of 10cm. The magnetic drum rotated at a speed of 200 revolutions per second and was scanned from 100- 200 read- write- heads. Five heads formed a band and gave a decimal digit, which was stored with five bit in an binary encoding.
On this relatively inexpensive, large memory up to 2000 words found space. The average access time could be reduced by the 2- address format from 2.4 to 0.8 milliseconds. Internally, the 650 worked with a binary error- detecting Encoding, making it very reliable.
Other features were:
- Diodes were suitable for industry and took over all gate functions
- Energy consumption was 18kW (previously 40kW)
- Cycle time: 8 microseconds for a processed decimal
- Signal level: -30V (inactive) to 10V (active)
