http://domino.watson.ibm.com/tchjr/journalindex.nsf/0/302607dfd49dc2f485256bfa00683fe8?OpenDocumentIt is a PDF document. But here is a simpler explanation. It is largely taken from .
BCROS consists of 8 bit-planes, 4 on each side of a 'gate' in the Central Processor Unit (CPU).
Four can be seen in this photograph above the person's back:
Each bit-plane is a copper clad laminate, approximately 203mm x 457mm, etched with a bit pattern.
|Mus.Cat. NEWUC:2003.31||Mnfctr: IBM||Date: 1967||Ser. No: 993309||Part No: 5737338-67|
|Comp: BCROS Plane||Length: 505 mm||Width: 211 mm||Thickness: 0.5 mm||Weight: 72 g|
A closer view is:
An even closer view shows the individual bits.
This type of read-only storage uses as a unit cell the capacitances formed at the intersections
of two groups of suitably shaped conductors,
the ones in the bit-plane are vertical and the others in the sense-plane are horizontal.
The selection of one data line causes voltage swing along that line,
which is capacitively coupled to the sense lines.
To ensure that the characteristic impedances and delays along the address and sense lines
are independant of the information patterns used, a balanced scheme is introduced.
Figure 2 "Flag" configuration showing two bits.
The address line has associated with it a balance line,
which contains a complementary pattern that couples it capacitively to the sense lines.
In other words, each bit is made up of the capacitive intersection of an data line
and a balance line with a pair of sense lines (Fig. 2).
Detection of stored data is accomplished by sensing differentially at the midpoint of the terminated sense lines.
Here are some photographs showing the individual bits of eight planes.
Take care they are 6 MBytes and will take a while to download on a slow Internet connection.
(5277312 and 5277313 are in fact the same part number, namely 5277312, and look like empty.)
(5737328 still has the rubbery sponge layer that distributed the pressure evenly.)
(5737332 has bits of the rubbery sponge still attached.)
5737330 5737332 5737335 5737336 5737338 5277312 5277313 5737328