Transfomer Read-Only Storage (TROS)

(Much of this is taken from an article by D.W.Taub & B.W.Kington
in the IBM Journal of research and development, September 1964.)

Read-only stores were used for many years from 1950 onwards
in telephone systems and digital computers.
Many different types were devised, each with advantages and disadvantages,
depending on the application.

Several read-only stores depended on the presence or absence of
mutual inductance between two circuits to determine whether a binary ONE or ZERO was stored.
One of them first described by T.L.Dimond in 1951,
has become known as the "Dimond ring" or transformer read-only storage.

Dimond's original store was used for code translations in the American No. 5 crossbar telephone system,
and for subroutines in the Bell Laboratories' Model 6 computer.
Later uses were the Atlas ground guidance computer,
and the stabilization data computer for Polaris submarines. (1951)

The example of its use in this exhibit is from a disk storage control unit
of an IBM 360 computer in 1967.

The control unit connected, along with others, to a channel that moved
data between the computer memory and devices asynchronously to the
computer processing unit's operation.

The TROS contained the microprogram that enabled the control of
up to eight disk drives connected to the unit.
TROS was not fast with a cycle time of 625 nsec and access time of 240 nsec,
which is three times slower than BCROS, but it was simple, rugged,
and provided large output signals.

The CCROS firmware was even slower at 750 nsecs.

TROS tapes
Here is a picture of a TROS module out of its assembly. Click on the thumbnail for a better view.

TROS diagram consists of flexible tapes printed with two pairs of ladder shaped conductors.

In between each pair of rungs in each ladder a square hole is cut,
which can accomodate the limb of the "U" part of a transformer core.
The "I" part of the transformer core had sense windings around it,
and is pressed against the "U" to make the "O" transformer core.

TROS closeup At each core limb position, holes are punched in one string of the ladder or the other,
making the electric current go through or around the core
depending on whether a ZERO or a ONE is to be at that position.

The original question was "So what is this computing artefact?"
The answer is a "A TROS assembly" of eight TROS modules.

Mus.Cat. NEWUC:2003.75 Mnfctr: IBM Date: 1967 Part No: 0768212 Eng.Chng: 551682
Comp: Firmware Width: 560 mm Depth: 85 mm Height: 576 mm Weight: 15.8 Kg

Each module had 64 tapes.
Each tape 2 words of 24bits.
So the whole TROS Assembly was 24,576 bits, or 3KByte of read-only storage.


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