On 26/03/2013 11:20 AM, scott wrote:
> On the Acorn there was no concept of CPU load as we have today - the CPU
> was always running at 100%.

Interestingly, this is apparently how MS Access 97 works. It always uses 
100% CPU. Because, in 1997, busy-waiting was an acceptable design decision.

http://www.youtube.com/watch?v=dOV5WXISM24

Post a reply to this message

On 26-3-2013 11:25, Orchid Win7 v1 wrote:
> Interestingly, there were several virus scanner programs for the Amiga,
> so clearly there were viruses around. I guess without the Internet, it's
> just that much harder to catch one...

They were spread through the exchange of floppy disks I seem to remember 
from my Amiga days ;-)

Thomas

Post a reply to this message

On 26/03/2013 12:58 PM, Thomas de Groot wrote:
> On 26-3-2013 11:25, Orchid Win7 v1 wrote:
>> Interestingly, there were several virus scanner programs for the Amiga,
>> so clearly there were viruses around. I guess without the Internet, it's
>> just that much harder to catch one...
>
> They were spread through the exchange of floppy disks I seem to remember
> from my Amiga days ;-)

That's probably why I never saw an actual Amiga virus. I didn't have any 
friends.

Post a reply to this message

On 26-3-2013 11:25, Orchid Win7 v1 wrote:
>>> The mouse was drawn as a hardware sprite overlay, so moving the mouse
>>> pointer involves poking new coordinates into some video registers. This
>>> takes a handful of compute cycles, and is easily implemented by a single
>>> interrupt handler.
>>
>> IIRC it was not even that. I don't have my hardware books lying around
>> anymore, but I think the horizontal and vertical motion of the mouse was
>> determined by two bit gray codes. These two bits were directly connected
>> to the video chip and the coordinates of the mouse were updated in
>> hardware. No interrupt required.
>
> I'm pretty much certain that's not correct.

well, they were directly connected to Denise and there were hardware 
counters in Denise for X and Y.

> Under sufficiently heavy CPU load, the mouse pointer became slightly
> less responsive. There's no reason for that to happen if it's all
> implemented in hardware.

I can not find the logic circuit of Denise, so perhaps you are right and 
the contents of the register had to be fetched and put in the mouse 
sprite x and y.

>> At the user level it was not fully preemptive. You had to do an explicit
>> call to allow other programs to get some time too.
>
> What in the world makes you think that?

Because I have written programs at that level.
It is a great way to avoid a busy wait on an event in a high level 
language. Just check if your condition is met, if not pass control back 
to the scheduler. Repeat until you have something to do.

What I remember from those days is that a process could be interrupted 
by a higher level process, but user programs ran until they voluntary 
gave control back to the scheduler.*

> If you run two programs that
> both try to use 100% CPU, they both end up getting approximately 50%
> CPU. (And everything else becomes fairly slow.)

Because all programs you used behaved decent and passed control to the 
scheduler regularly? Remember we are thinking about a multitasking 
single user machine. There is no point in annoying the user by not 
giving other programs a change to run. There is not even a point in 
trying to get more than your fair share. But see the note below.

*) trying to google things, the wiki page on Exec_(Amiga) claims that 
linus once mistakingly said that AmigaOS was cooperative. In earlier 
versions of this page it *was* apparently considered cooperative, 
because google quotes a text that is no longer there. Another source 
says that the first version of AmigaOS was cooperative, implying that 
later versions weren't. Possibly I have been programming the earlier 
version and later versions indeed were fully preemptive, but the system 
calls still worked, so I did not notice the change.
For what I needed cooperative multitasking was exactly what I needed. 
E.g I had a multichannel dataacquisition running on a PC that was 
connected to the Amiga over a parallel port. I had one channel live in a 
separate screen** and a data analysis program that could use the same 
parallel connection to get the full data of a part of the recording. On 
the Amiga side I had several programs running, all cooperatively, 
including the parallel communication program (a sort of device driver 
but at user level). On the PC side I had to solve it with one big event 
loop.

**) for the non-amiga users: the Amiga was able to display several 
'screens' at the same time. Each with its own resolution and color 
depth. Transistions between screens were always at a horizontal line and 
the display line where that happened was handled by another custom chip. 
You could move a screen in front of another revealing or hiding as much 
as you wanted.

Post a reply to this message

On 26-3-2013 17:09, Orchid Win7 v1 wrote:
> On 26/03/2013 12:58 PM, Thomas de Groot wrote:
>> On 26-3-2013 11:25, Orchid Win7 v1 wrote:
>>> Interestingly, there were several virus scanner programs for the Amiga,
>>> so clearly there were viruses around. I guess without the Internet, it's
>>> just that much harder to catch one...
>>
>> They were spread through the exchange of floppy disks I seem to remember
>> from my Amiga days ;-)
>
> That's probably why I never saw an actual Amiga virus. I didn't have any
> friends.

LOL. I didn't meet any virus either but at work one guy was a huge 
collector of all kind of more or (mostly) less legal copies of Amiga 
software, and he regularly struggled with virus problems.

Thomas

Post a reply to this message

On 23/03/2013 8:48 PM, Jim Henderson wrote:
> On Sat, 23 Mar 2013 20:23:19 +0000, Stephen wrote:
>

>>
>> I never really took to Willie R. Too much of a middle class snob to my
>> mind. He was funny, though.
>
> I don't know much about Willie other than that I found him funny on
> Clue. :)  But he often had one-liners that would just bring the house
> down, and even the other guys who were on the team at the time just don't
> have the comedic sense of timing that he did.
>

I’m sorry, I thought that I had replied to you. I had a BSOD which wiped 
my own memory as well.

I grew up thinking Willie Rushton was the bee’s knees. Then, as I grew 
aware of the world, I found his right ling views unpalatable. I can’t 
hear recordings of him now without hearing a pompous, self regarding, 
smart arse, too full of his own self importance. But he was funny.

> About the closest they come now to that kind of timing is in the game
> Word for Word, when (almost always as the second word), Tim will say
> "Pardon?" and then the other player will repeat what he said previously,
> to which Tim says "No, that was my word."
>
> That one makes me chuckle every time, even though it's entirely
> predictable.
>

I thought that it was Graeme who did that.

>>> And Humph.  Jack's getting the 'curmudgeon' routine down well,
>>> but nobody does it the way Humph did.
>>>
>>>
>> That is Jack Dee's normal persona. He does well but Humph had years on
>> the rest of the team and could look on everyone with the contempt of an
>> adult with adolescents. He does very well but he is a youngster amongst
>> giants. I think that in the long run they would have done better picking
>> someone else as the chairman, someone with a different style. Maybe
>> supper nannie. ;-)
>
> Yeah, I've seen Jack on QI and a few other things (Kingdom, IIRC), and it
> does seem to be something even his characters have in common with him.
> But I don't know who else they could've picked - they couldn't "promote"
> any of the panelists because that just wouldn't work - that group of
> panelists works well together,

Indeed that is true.

> even with the floating guest spot (which
> they really should just let Rob Broydon fill full time),

I like the variety, one day they might get Nicolas Parsons.

> but putting
> Barry or Graeme in charge (I couldn't see Tim doing it) would change the
> entire dynamic.
>
> But I think Jack does his own thing - he doesn't try to be Humph, and
> that's a good thing.  I think if he did that, it wouldn't work at all.
> His demeanor is similar, but also distinctly different.
>

He does the best at an impossible job - filling Humph's boots.

-- 
Regards
     Stephen

Post a reply to this message

>> I'm pretty much certain that's not correct.
>
> well, they were directly connected to Denise and there were hardware
> counters in Denise for X and Y.
>
>> Under sufficiently heavy CPU load, the mouse pointer became slightly
>> less responsive. There's no reason for that to happen if it's all
>> implemented in hardware.
>
> I can not find the logic circuit of Denise, so perhaps you are right and
> the contents of the register had to be fetched and put in the mouse
> sprite x and y.

That was my understanding. The hardware may well be in the same chip, 
but it's under software control. (Like I said, it only takes a few 
op-codes to copy the X and Y coordinates from one pair of registers to 
another.)

>>> At the user level it was not fully preemptive. You had to do an explicit
>>> call to allow other programs to get some time too.
>>
>> What in the world makes you think that?
>
> Because I have written programs at that level.
> It is a great way to avoid a busy wait on an event in a high level
> language. Just check if your condition is met, if not pass control back
> to the scheduler. Repeat until you have something to do.
>
> What I remember from those days is that a process could be interrupted
> by a higher level process, but user programs ran until they voluntary
> gave control back to the scheduler.*

> *) trying to google things, the wiki page on Exec_(Amiga) claims that
> linus once mistakingly said that AmigaOS was cooperative. In earlier
> versions of this page it *was* apparently considered cooperative,
> because google quotes a text that is no longer there.

http://en.wikipedia.org/wiki/Exec_%28Amiga%29

"Exec is the multi-tasking kernel of AmigaOS. It enabled pre-emptive 
multitasking in as little as 256k of memory (as supplied with the first 
Amiga 1000s). Exec provided functionality for multi-tasking, memory 
allocation, interrupt handling and handling of dynamic shared libraries."

Sounds pre-emptive to me...

In particular, like several other fully pre-emptive systems, Exec 
provides Yield(), which lets you relinquish the rest of the current 
quantum if you wish. However, if you do not call this, a hardware 
interrupt causes Exec to perform a context switch to the next runnable 
task, in round-robin fashion, whether you ask for it or not.

Indeed, were Exec not pre-emptive, there would be no need for Forbid() 
and Permit(), which disable and enable pre-emption. (It's apparently 
used as a crude form of critical section.)

Now, if you mean that a lower-priority task can never run until all 
higher-priority tasks go to sleep, then yes, that's how the scheduler 
works. Usually the very high-priority tasks were things like the 
keyboard scan, which run for a tiny amount of time and then sleep again.

Post a reply to this message

On Wed, 27 Mar 2013 10:56:20 +0000, Stephen wrote:

> I’m sorry, I thought that I had replied to you. I had a BSOD which wiped
> my own memory as well.

:(

> I grew up thinking Willie Rushton was the bee’s knees. Then, as I grew
> aware of the world, I found his right ling views unpalatable. I can’t
> hear recordings of him now without hearing a pompous, self regarding,
> smart arse, too full of his own self importance. But he was funny.

That's a shame.  I feel kinda the same way about Jeremy Hardy, even 
though his leanings are similar to mine (but a bit more to the left).  
There are places where comedy and politics play well (and he uses this to 
great effect on The News Quiz), but other places where it doesn't belong.

>> About the closest they come now to that kind of timing is in the game
>> Word for Word, when (almost always as the second word), Tim will say
>> "Pardon?" and then the other player will repeat what he said
>> previously, to which Tim says "No, that was my word."
>>
>> That one makes me chuckle every time, even though it's entirely
>> predictable.
>>
> I thought that it was Graeme who did that.

That could be.  It's usually late when we're listening. :)

>> even with the floating guest spot (which they really should just let
>> Rob Broydon fill full time),
> 
> I like the variety, one day they might get Nicolas Parsons.

The variety is nice - it was fun to listen to a show from series <mumble> 
with Sandi Toksvig on it.  She made a joke about being proud to be one of 
a long list of female guests they'd had on the show, and it went over 
very well. :)

>> but putting Barry or Graeme in charge (I couldn't see Tim doing it)
>> would change the entire dynamic.
>>
>> But I think Jack does his own thing - he doesn't try to be Humph, and
>> that's a good thing.  I think if he did that, it wouldn't work at all.
>> His demeanor is similar, but also distinctly different.
>>
>>
> He does the best at an impossible job - filling Humph's boots.

That's the truth, no mistake about that.

Jim

Post a reply to this message

On 27/03/2013 9:42 PM, Jim Henderson wrote:
> On Wed, 27 Mar 2013 10:56:20 +0000, Stephen wrote:
>

>
> That's a shame.  I feel kinda the same way about Jeremy Hardy, even
> though his leanings are similar to mine (but a bit more to the left).
> There are places where comedy and politics play well (and he uses this to
> great effect on The News Quiz), but other places where it doesn't belong.
>

It is not a problem, nowadays. ;-)
True, some comedians have only one string to their bow. We had one, who 
died this month, whose act consisted of speaking as if his microphone 
was intermittent. He got thirty years of work out of it.


>>>
>> I thought that it was Graeme who did that.
>
> That could be.  It's usually late when we're listening. :)
>

I know, that late night interference on the shortwave radio can be 
dreadful. :-P


> The variety is nice - it was fun to listen to a show from series <mumble>
> with Sandi Toksvig on it.  She made a joke about being proud to be one of
> a long list of female guests they'd had on the show, and it went over
> very well. :)
>

That must have been the series when H&D did Hogmanay at the Big Hoose.



-- 
Regards
     Stephen

Post a reply to this message

On Thu, 28 Mar 2013 10:20:14 +0000, Stephen wrote:

> On 27/03/2013 9:42 PM, Jim Henderson wrote:
>> On Wed, 27 Mar 2013 10:56:20 +0000, Stephen wrote:
>> That's a shame.  I feel kinda the same way about Jeremy Hardy, even
>> though his leanings are similar to mine (but a bit more to the left).
>> There are places where comedy and politics play well (and he uses this
>> to great effect on The News Quiz), but other places where it doesn't
>> belong.
>>
> It is not a problem, nowadays. ;-)
> True, some comedians have only one string to their bow. We had one, who
> died this month, whose act consisted of speaking as if his microphone
> was intermittent. He got thirty years of work out of it.

Can't fault him for continuing to do something that works. :)

>>> I thought that it was Graeme who did that.
>>
>> That could be.  It's usually late when we're listening. :)
>>
> I know, that late night interference on the shortwave radio can be
> dreadful. :-P

It's pretty awful, I will admit. :)

>> The variety is nice - it was fun to listen to a show from series
>> <mumble>
>> with Sandi Toksvig on it.  She made a joke about being proud to be one
>> of a long list of female guests they'd had on the show, and it went
>> over very well. :)
>>
> That must have been the series when H&D did Hogmanay at the Big Hoose.

H&D?

Jim

Post a reply to this message