Transformer read-only storage

[1] TROS was considered simple in design, albeit with flaws that discouraged later applications due to demands for higher computer performance.

TROS used stacks of removable Mylar flexible printed wiring sheets that fitted onto fixed transformer bases.

[2] The design of TROS is based on induced current from wires passing through magnetic ring-shaped transformer cores.

[3] Later designs for the IBM System/360 had removable sheets of Mylar with embedded copper wiring as the word lines.

[1][2] The copper wiring would be arranged in a grid-like pattern, with some lines disconnected to allow the current to pass through or around a core.

In 1959, TROS was used in the Scientific Computer and Modular Processor (SCAMP) project by the IBM Hursley team.

[2] This version of TROS had sheets of Mylar with copper wiring, making manufacturing and code adjustments easier.

Larger models of the System/360 would alternatively use the faster balanced-capacitor read-only storage (BCROS) to accommodate the desired higher performance.

Typically, word lines that needed to be changed were disconnected and left in the system, while a new wire was threaded.

[8] This limitation was overcome with the use of Mylar sheets, allowing for easy removal and installation of new word lines.