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Apr 5, 2014

Digital's DECSYSTEM-20 - Part 4 - Input/Output for CPU


The I/O cabinet connected the main processor KL10 to the peripherial devices via MASSBUS or UNIBUS (see the following picture). MASSBUS was for fast and large amounts of data transfer and UNIBUS was for slow terminals, printers and similar.

DECSYSTEM-20 block diagram

LIST OF PARTS (see block diagram above)

The I/O cabinet did not contain anything else but handshake logic for the 2 buses. DTE20 handled the UNIBUS and RH20 handled the MASSBUS. Some versions had also memory racks in the cabinet # 2 either on the back door or at the back of the cabinet. This version had 2 MF20 memory assemblies in it.

Cabinet # 2: Input/Output logic for CPU
  • DTE20  -  Ten-Eleven Interface Unit (PDP-10 to PDP-11 Interface Unit)
  • RH20  -  MASSBUS to CPU channel bus (internal) Interface Controller
  • MF20  -  Memory
  • MF20  -  Memory

Here is the I/O cabinet in more detail. Most visible are the wire wrapped back planes. Automatic machines were used to wrap those. Heavier power wires connect to the left where the power supplies are.

Front view of the cabinet # 2 (I/O cabinet)

Rear view of the cabinet # 2 (I/O cabinet)

Here is the I/O card cage and MF20 block in more detail.

I/O card cage modules

Typical MF20 module utilization

1957 Digital opened for business with three employees and 8,500 square feet of production space in a 19th-century woolen mill.

DEC Production, women working in main assembly area, ca. 1960

The old Assabet Woolen Company mill complex in downtown Maynard became the home of Digital Equipment Corporation 1957

[The next part of this article will cover the CPU cabinet.]


/1/ MP01708_KL10-R_System_Drawings_Sep83.pdf

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