Abstract: An external clock unit for use with a DEC 6000 series computer for increasing the clock cycle time includes an oscillator for generating a clock signal which is faster than the clock signal produced by the oscillator in the CPU module in the computer, a line driver for driving the clock signal outputted by the oscillator in the clock unit, a manually operable switch for outputting a control signal and a power supply for providing power to the various components in the clock. In use, the external clock unit is connected to the clock distribution chip in the CPU module in the computer using pins normally used only for test purposes during fabrication. When the switch is turned on, the clock from the oscillator in the computer CPU module is disabled and the clock signal from the clock which is received by the clock distribution chip is used as the clock signal for the computer.

Abstract: An external clock unit for use with a DEC MICROVAX model 31 computer includes a first crystal oscillator for generating a clock signal of about 44 MHZ, a second crystal oscillator for generating a clock signal of about 63 MHZ, a 2 to 1 multiplexor for receiving 44 MHZ clock signal and the 63 MHZ clock signal and outputting one of clock signals, a first switch for selecting which of the two clock signals is to be outputted by the 2 to 1 multiplexor, a second switch for selecting which one of two logic signals is to be outputted by a system identification code generator in the computer and a power supply for providing power to the device. In use, the external clock unit is connected to jumper pins on the processor clock signal line and the system identification code generator.

Abstract: An external clock unit for use in increasing the clock cycle time in a DEC 8000 series computer without making any hardware changes inside the computer includes a first crystal oscillator for generating a first clock signal 160.2 MHZ, a second crystal oscillator for generating a second clock signal, a multiplexor for receiving said first clock signal and said second clock signal and outputting one of said clock signals, a first line driver for driving the clock signal of 157.53 MHZ outputted by the multiplexor, a second line driver for outputting a clock enable signal, a toggle switch for turning on the clock enable signal and a power supply for providing power to said first crystal oscillator, said second crystal oscillator, said multiplexor and said first and second line drivers. In use, the accelerator is connected to the clock module in the computer through pins in the backplane.