🚀 go-pugleaf

In <1990Sep17....@hq.demos.su>, Vadim G. Antonov posted:

	Another piece of BESM's hardware is a drum printers ACPU-128
	(stands for Alphabetic-Numeric Printing Device, oh days of yore!)
	These printers have a funny control: each hammer can be moved
	by setting or clearing bits in the register. Interrupt per
	each rotating drum position generated. So, driver should catch
	interrupts and recalculate positions of hammers. As a result
	the best printer driver takes 12% of CPU per one device.
	Another feature of such printer control is *very* funny:
	if driver failed to handle interrupt at a time the line of garbage
	appeared. One can also calculate a loading of the machine by
	measuring distances between baseline and letters.

	Vadim Antonov
	DEMOS, Moscow, USSR
	(It is NOT a joke!)

Well, America had its share of really dumb printers too.

I recall how the 1132 printer (part of the IBM system 1130)
was similar, but it was SO DUMB that
missing an interrupt caused the printer to fire the hammers
for the same character positions for the next character.

Simple way to make a lot of noise:
	set the printer buffer to all one.
	issue "start printer" command
	halt the CPU
The printer will fire ALL 132 hammers for every character, not
stopping until the printer's STOP button was pressed.

The 1132 printer didn't use a drum: it had 132 print wheels all
spinning together, but the individual wheel was kicked back by the
hammer to hit the paper from the front.

I recognized the paper tractor mechanism and carriage control
tape from a brochure for "accounting machines".

The CPU overhead was rather low: it interrupted for every character
and read its buffer directly using DMA.   The driver just had to
fill the buffer before the characters came into position.

Now my printers all have buffers and their own CPU.
They're harder to confuse.  They're no fun anymore.

Jeffrey Jonas
jeffj@synsys.uucp