Dev.SN

Transatlantic Ping Faster than Sending a Pixel to Screen

posted by mrcoolbp on Friday March 28 2014, @05:40AM   
from the 1ms-2ms-3ms-floor dept.

Anonymous Coward writes:

Two years ago John Carmack tweeted, "I can send an IP packet to Europe faster than I can send a pixel to the screen. How f'd up is that?" And if this weren't John Carmack, I'd file it under the interwebs being silly.

Not convinced? You aren't alone, but Carmack appeared when called out to defend this claim.

We looked further and found this informative article from AnandTech about input lag.

• Re:Gone backwards? (Score: 0) by Anonymous Coward on Friday March 28 2014, @09:24AM

  by Anonymous Coward on Friday March 28 2014, @09:24AM (#22494)

  Your fast update also excludes the whole "read
  user input and figure out what to do with it"
  part. TFA suggests ~10-100ms for that on a modern
  computer; I'd guess 2-5x that on your Sinclair,
  for a contemporary game.

  I wouldn't be so sure about that. I don't know about the sinclair, but on the C64, the keyboard was laid out (electronically) in an 8x8 matrix, connected to two memory mapped 8 bit parralel ports. Although you do say "game", which is completely different from Carmacks test. For his test, which only needs to poll one key, you could set up one port ahead of time to the correct row (assuming interrupts disabled), after which polling the port is a single instruction plus a branch if the port read as zero. Updating the screen background color is a third instruction. Along with a jump back to the test, that's four instructions for the entire test routine (after setting up everything), and the jump is not time critical.

  Even with 1 MHz, three instructions is pretty fast.

  Parent