Weekly Classic Computer Trivia Question (20150112)

Johnny Billquist bqt at update.uu.se
Mon Jan 12 12:42:54 CST 2015

On 2015-01-12 19:34, Vincent Slyngstad wrote:
> From: Johnny Billquist: Monday, January 12, 2015 10:17 AM
>> Interrupt driven mass storage was (and is) pretty uncommon, because it
>> requires so much CPU. But of course, for those who do, you transfer
>> only at interrupt time, so you are not bound by the disk speed anyway.
> For other systems maybe, but for the PDP-8, not so much.

The one I can recall off my head (unless my brain is fooling me) is the 
RX8. And it's definitely true for that one.

If you are thinking of the TD8E then you need to remember that this 
controller is not even interrupt driven. It is a purely polled 
controller. And that one is truly horrible, and difficult to even use in 
an interrupt driven system. It can be sortof made to work with the help 
of timers, calculations, and temporarily turning off interrupt when you 
want to do the actual transfers, as it cannot tolerate anything else 
interrupting the code while a transfer is in progress.

>> And of course, you also have things like OS/8, which runs with
>> interrupts off at all times, to which the answer to the original
>> question would be "OS/8". :-)
> Exactly :-)

But anything running constantly with the interrupts off should not be in 
the "competition". As it's hardly called latency when you just ignore 
the signal.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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