Conclusion
Core memory was the leading memory technology from the mid-1950s until it was replaced by semiconductor memory in the early 1970s. For its time, core memory provided dense, reliable, and inexpensive storage, but memory technology has improved incredibly since then. The 1401 had a 11.5 microsecond memory cycle time, compared to 5 nanoseconds for modern RAM. While the 1401 had 4000 characters of storage (expandable to 16K), modern computers have many gigabytes. Adding a 4K memory expansion to the 1401 cost $20,100 ($162,000 in current dollars). Now a 16 gigabyte memory costs under $100. But even though it is obsolete, core memory is still an interesting technology to examine.Thanks to the members of the 1401 restoration team and the Computer History Museum for their assistance The IBM 1401 is demonstrated at the Computer History Museum on Wednesdays and Saturdays (subject to hardware problems) so check it out if you’re in Silicon Valley (schedule).
References
The IBM 1401 core module is documented in detail in 1401 ALD 42 and 1401 Instructional Logic Diagrams. For more information on core memory, see Coincident Current Ferrite Core Memories and Magnetic Core Memory Systems.
Original article written by Ken Shirriff at his blog.
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