The Univac Solid State Computer 90, The Read-Punch-Unit.

	Left: the RPU-console

The Read Punch Unit.

The Read-Punch Unit could feed a punch-card, read it, punch it and read it again 
and put the card into one of the two output-bins. 
Data could be punched into prepunched cards.
In one cycle of the read-punch-unit the programmer had to deal with four different cards:
read the fourth, punched the third, check-read the second and lay down the first that entered the device.
The Read-punch-unit could read and punch 150 cards per minute.
Programming the RPU:
The instruction 81 4000 0530 would punch data from the 4000-band into the card in the punch-station and simultaneous read two cards,
one before the punching and one after, and write these card-images into the buffer.
The instruction 22 0820 0505 then tested whether the read-station-buffer already had been written.
On a yes the instruction 46 3800 0560 would transfer the two card-images from the buffer to the 3800 band.
The instruction 57 0000 0590 selected the card just red in the second reading-station to fall into bin 2 the next cycle.
Not selected cards ended up in bin 1.



                                                          Schedule of the timing of the punch-cards in the read-punch-unit 


Programming the Read Punch Unit was complicated since the program had to interact with the five positions of the cards.
To simplify this, Univac had provided punch-routines to be incorperated into the programs.
The Read Punch was also used to punch tested and debugged programs from memory into machine-code-cards,
because then they were easier to handle, and was used to duplicate data-files.
In programs it punched aggregated data in cards to be used by succeeding programs.

For instance: 
when calculating wages from a merged file with employee-data and worked-hours- data, 
a payment-list was printed and at the same time, cards were punched with financial-data for accountancy and for the project-administration.