CROS

Capacitor Read Only Storage

Note: ROS [Read Only Storage] is a generic term within the System/360 family. It is implemented differently (in terms of physical hardware) in different models. In the Model 65 - and several other models - tiny capacitors are used to represent the bits; 1s or 0s. This implementation is called CROS [Capacitor ROS]. On this page, as in the IBM documentation, the terms ROS and CROS are used interchangeably depending on the context.

Below is an illustration of the differences in ROS field (micro-order) structure between the standard and FAA Model 65s. It can be seen that 'spare' bits in the standard Model 65 have been allocated new functions in the FAA Model 65. It is significant to note that nothing has been taken away from the standard machine's ROS, functions have just been added.

CROS bit listings

CROS bit listings for the FAA Model 65. Click on the "QZXXX" links to view the listings. The third column in the listing, headed "CLD", gives the number of the Control Automation System (CAS) Logic Diagram (CLD) page the block appears on (e.g. QY051) and the 'grid reference' of the block on the page (e.g. N8). The main part of the page shows the actual bits (0 or 1) broken down into control fields (see the table above) and parity bits. Note the only unused bit in each ROS word is the second bit (bit 01) which is set to 0 in every ROS word.

Bit listing for CROS plane 01 (0): QZ001 

Bit listing for CROS plane 02 (1): QZ011

Bit listing for CROS plane 03 (2): QZ021

Bit listing for CROS plane 04 (3): QZ031

Bit listing for CROS plane 05 (4): QZ041

Bit listing for CROS plane 06 (5): QZ051

Bit listing for CROS plane 07 (6): QZ061

Bit listing for CROS plane 08 (7): QZ071

Bit listing for CROS plane 09 (8): QZ081

Bit listing for CROS plane 10 (9): QZ091

Bit listing for CROS plane 11 (A): QZ101

Bit listing for CROS plane 12 (B): QZ111

Bit listing for CROS plane 13 (C): QZ121

Bit listing for CROS plane 14 (D): QZ131

Bit listing for CROS plane 15 (E): QZ141

Bit listing for CROS plane 16 (F): QZ151


Below is a picture of a Model 50 CROS plane. It is the same as a Model 65 CROS plane except for the specific bit representations. Click on it to open a larger image.

Bit listing text file

Here is a text file which contains a bit listing of the complete contents of the 7201's CROS. The first column is the ROS address, followed by bits 0-99 grouped into control fields and parity bits. It was OCR'ed from the QZ CAS pages above and manually corrected as far as possible. It is believed to be accurate but this cannot be guaranteed.

CROS.txt

CAS logic block listings

Control Automation System (CAS) logic diagrams. These diagrams symbolically show in a block the control fields for each ROS word as listed in raw form in the bit listings above. They are effectively flow charts that depict the jumps and branches of the machine microcode.

CAS microprogram logic diagrams QA pages: QA001

CAS microprogram logic diagrams QB pages: QB001

CAS microprogram logic diagrams QC pages: QC001

CAS microprogram logic diagrams QE pages: QE001

CAS microprogram logic diagrams QF pages: QF001

CAS microprogram logic diagrams QG pages: QG001

CAS microprogram logic diagrams QJ pages: QJ001

CAS microprogram logic diagrams QK pages: QK001

CAS microprogram logic diagrams QP pages: QP001

CAS microprogram logic diagrams QQ pages: QQ001

CAS microprogram logic diagrams QS pages: QS001

CAS microprogram logic diagrams QT pages: QT001

CAS microprogram logic diagrams QU pages: QU001

CAS microprogram logic diagrams QY pages: QY001