How core memory is mounted in the 1401
The following picture shows the core memory module mounted in its rack, along with the many SMS cards required by the core module. (IBM built computers from Standard Modular System cards, each about the size of a playing card and holding a few transistors and other components.) At the left are the driver cards and current source cards that drive the matrix switch boards, and the driver cards for the inhibit lines. The next column holds the address decode cards. The address lines plug into the empty sockets at the bottom. The next column holds the sense line pre-amplifier and amplifier cards. The core module itself is mounted with the matrix switch cards on top. At the far right are the sockets for the hundreds of wires from the brushes and print hammers.
Core memory module and associated circuit board from an IBM 1401 mainframe. Photo courtesy of Rob Storey.
The photo below shows the core module mounted inside the IBM 1401 mainframe, looking into the left end of the computer. The core module is behind the bundle of black and yellow wires, mostly address lines. The matrix switches are on the left. The colorful brush and hammer wires are connected via paddles underneath the core module. The SMS driver cards are above the core module, mostly behind a metal cover for airflow.
The core memory module inside the IBM 1401 mainframe. The module is in the lower right, with the driver cards above.
The photo shows some other interesting features of the 1401. At the top of the computer is the time meter that records how much time the computer has been running. IBM usually leased the 1401 and if you used the computer more than 8 hours per day, they would charge you for the excess. (Unless, of course, you paid for the 24/7 lease.) In the upper right is the “convenience” outlet located inside the computer, a standard electrical outlet. Below the outlet is the wiring on the back of the front console. The computer didn’t use a backplane; instead, many loose bundles of wires connected circuitry modules, as you can see at the bottom of the photo.
