[flashman]

> Sidebar: A note on frames per second. The European PAL C64 updated at 50fps, whereas the US NTSC systems updated at 60fps

This is because alternating current is 50Hz in PAL countries (eg Europe), and 60Hz in NTSC countries (eg America). Analogue TVs vertical refresh rate was synced to the AC frequency for a bunch of practical reasons, which meant gaming consoles had to send signals to the television at either 50Hz or 60Hz.

Result? Many PAL console games actually ran at 5/6ths of NTSC speed. Most notoriously, Sonic the Hedgehog, whose agility was more sluggish (and soundtrack less vivacious) for a large fraction of the world. More information in this video: https://www.youtube.com/watch?v=cWSIhf8q9Ao

[eriknstr]

In a similar fashion, some turntables have four rows of dots on their platter and a strobe light that will blink at a frequency determined by your mains AC frequency, and when the platter is moving at a perfect 33 RPM or 45 RPM, the respective row of dots for your AC frequency will appear to be standing still.

https://www.youtube.com/watch?v=LdyiFn_idpY

[mschaef]

Synchronous clocks do this too... they've driven by a motor that's designed to work in phase with the electrical grid's frequency. This means they rotate at a fixed speed and can be used as a time base for a clock.

From the perspective of the grid operator, however, 50 or 60Hz is not always 50 or 60Hz. A sudden load or a generator tripping offline (to preserve itself) results in a transient slowdown of the frequency of the entire grid. I spent a summer in high school helping out with the analysis of these kinds of disturbances, and there's a distinct pattern to the fluctuation of grid frequency. There are also slight longer term errors in grid frequency, although operators are held to strict standards.

Getting back to clocks, integrating these transient frequency errors over time results in clocks that shift forward and backward relative to real time. This integrated time error is often displayed in grid control rooms, and it is something they deliberately manage to ensure that the 'grid time' is accurate. In practical terms, this means a period of ever so slightly less than nominal frequency is likely to be followed by a period of deliberately induced slightly higher than normal frequency, so that the overall integrated error tends to zero.

More details on the time control aspect on page 13 here: http://www.nerc.com/docs/oc/rs/NERC%20Balancing%20and%20Freq...

[eriknstr]

I previously worked with Unix sysadmin tasks and software development at Statnett SF [1], the transmission system operator (TSO) for the national level of the Norwegian electrical power distribution network, and am currently studying at the university to become an electrical engineer. We started learning about transformers, generators and motors in three-phase systems this semester, so that document is of interest to me. I looked over the document briefly and intend to read it in full later, for example tomorrow when I will be going on a two hour train trip to Oslo.

The electricity sector in Norway relies predominantly on hydroelectricity. In 2008, hydroelectricity generated 141 terawatt-hours (TWh) and accounted for 98.5% of the national electricity demand. [2]

I have been told that the nature of hydroelectric power generator installations makes the act of balancing the power system in Norway quite different from what most other countries are dealing with but I think the document you linked will be informative to me none-the-less. Besides, understanding power systems balancing in general and not just for Norway would allow me to work in other countries in the future should I want to. Not saying that the university is going to teach me things that apply to Norway only of course but I hope that you understand what I mean.

PS: Statnett has a live view of the Nordic power balance on their website -- http://statnett.no/en/Market-and-operations/

[1]: http://statnett.no/en/About-Statnett/

[2]: https://en.wikipedia.org/wiki/Electricity_sector_in_Norway

[mschaef]

Cool... good luck! (If you ever find an intuitive way to think about reactive power, please let me know... I get it in broad strokes, I've been trying to wrap my head around the details for over 20 years, off and on.)

> I have been told that the nature of hydroelectric power generator installations makes the act of balancing the power system in Norway quite different from what most other countries are dealing with

Hydro has both upsides and downsides. To the upside, they're easily able to respond to changes in demand. It's the difference between opening a wicket gate and adding fuel/air to boil more water, to make more steam, to apply more torque. Hydro can also support stored power.... sometimes you see what are known as pumped storage generators generate 'negative' output. This means they're running as a motor to pump water up a hill. When power is needed they can just drain the water through turbines to generate power.

That said, Hydro also has additional constraints on operation that can be imposed by flood control requirements, reservoir levels [1], environmental regulations, etc.

1] https://wrrc.arizona.edu/drought-diminishes-hydropower

[rusk]

> for a bunch of practical reasons

Basically makes it cheaper to build. You have a natural frequency there to use, and you don't have to come up with all this additional hardware to smooth out the existing frequency and come up with a new one.

I think there was a flip-side to this ... though NTSC had faster refresh, PAL had a higher resolution (more lines). I'm not sure, but I think this may have been a tradeoff.

[ldite]

It also reduced the effects of mains interference. If you had a 60Hz vertical scan, but there was interference from 50Hz mains (as there often was) then this would cause rapid rolling vertical distortion.

At 50Hz, even if the vertical sync wasn't actually locked to the mains frequency, any mains distortion would roll much, much more slowly, and be less offputting.

[mdpye]

You are correct. A black bar at the bottom of the screen is a nostalgic trigger for me! (When playing games which were designed for NTSC resolution on PAL screen. This was a generation later on the Amiga)

[boomlinde]

With analog TVs, it's the signal source that generates the synchronization signal. For the C64 specifically, like all the home computers and video game systems I know, this is derived from a crystal, not mains A/C. Since you need a pixel clock and horizontal clock at consistent multiples of the vertical draw time, using mains to derive the video sync seems very impractical.

My (basic) understanding is that having the beam move at roughly the same frequency as the A/C current is done to mitigate noise and distortion caused by other appliances, which earlier tubes were much more susceptible to.

[simias]

You have more lines with PAL but in practice since most of the game devs were either in Japan or in the US (with a few notable exceptions) most games were designed for NTSC and many didn't bother to increase the resolution when porting to PAL. Furthermore many games refreshed the display at half the video framerate so you end up with 25fps on PAL.

So in many cases you end up with games that run at 5/6th the nominal speed and have black bars at the top and bottom of the screen. PAL gaming was pretty crap, but of course at the time I didn't know any better and I didn't understand english anyway, so it's not like I had a choice...

[anticodon]

> Basically makes it cheaper to build. You have a natural frequency there to use, and you don't have to come up with all this additional hardware to smooth out the existing frequency and come up with a new one.

I'm not an expert, but I read that it was the idea but it was never implemented and TVs used independent generators.

[MatthewWilkes]

I recently modded my Master System to have composite out and added a 50/60 switch at the same time. Flipping it in-game feels really strange, as I'm so familiar with the PAL speed, but the NTSC speed is obviously the correct one.