klog

Tired of my laptop dying every now and then, I have taken drastic action.

The Acer Travelmate 2420 is very badly designed where it comes to heat management. Air is sucked in from under the laptop (where your leg or the table would block the airflow) and blown out the side of the machine. A smarter arrangement might be to suck in air from above the keyboard and blow it out the side, but hell - what do I know about laptop design…

Anyway - the problem is that the bottom hole is too easily blocked, and besides, the fan is crap - doesn’t pull in enough air.

The solution is to give the fan a helpful boost. So, what I did was to build a small platform from cardboard, and stick three Thermaltake fans in it, each of which was more powerful than the laptop fan. This causes a large airflow through the laptop, keeping the usually-roasting right side of the machine actually colder than the rest of the machine!

1. front view - laptop is at perfect angle for working at. 2. back view - shows the three fans. 3. left view - my hacked power-supply (normal four-wire power cable with two of the wires hooked to a 12v PSU). 4. top view - shows the air hole which sits directly under the laptop fan, and a cardboard block at the bottom middle which helps keep the laptop in place (along with the two grooves on either side).

Yesterday, I backed up my /home/kae directory, formatted the computer, and installed Windows XP. Why? Because I felt the need to spend the next week playing the Thief and Dungeon Keeper games series. I really wanted to do it through ‘98 (yes, I still have the licenses for these OSes), but couldn’t get drivers for my laptop for Windows 98 - the Acer TravelMate 2420 just will not work in Win98…

So anyway - a blissful day later, I decided I should put my system back together. Installed Partition Manager, shuffled the hard-drive around to make space, and got the Fedora 8 disc from the latest Linux Format (/nice/ desktop theme, lads! Much better than that weird balloon crap in FC7).

Stuck the DVD in, rebooted, and …GRIND…

oh dear… tried again. …GRIND…

tried with one of the games CDs that had been working fine for the last day …GRIND…

I worried about this for a few minutes before opening the drive up and taking a look to see if there was something blocking the lens’s path. nope.

It took me a while to notice though that the lens was parked on the /outside edge/ of where a disk would be. As the file allocation table for a CD/DVD is held on the inner rim of the disk, it does not make sense for the lens to be parked far from it when not in use.

I pushed the lens platform in with my finger. I really don’t like doing things like that, as I might be breaking something by doing it, but as the system was already screwed, this was a viable solution.

On rebooting, everything worked fine.

What seems to have happened is that at some point over the last few hours, the lens platform must have moved a little bit too far and was unable to return to its usual route. I am not sure why that happened, as I can only imagine it would happen if I was over-burning something, which I haven’t done in a long time.

Anyway - back to resetting my system, and then back to Dungeon Keeper!

ps: this post, boring as it is, is out there purely because I spent a while trying to find the cause of the noise and disc-drive failure and had to figure it out myself in the end - hopefully someone else searching for “grinding noises dvd” will find this post useful.

When i was 6th class in primary school, we had just finished the primary maths curriculum and had a few days to spare, so the teacher decided he’d try teach us a bit of algebra.

As a test of our out-of-the-box thinking, he posed this little puzzle:

Given a triangle of balls, where there are x balls on the bottom, x-1 above that, x-2 above that, and so on until there is only one on top, how can you figure out x if you are given the overall total y

    O
   O O
  O O O
 O O O O
O O O O O
x=5, y=15

In other words, if x is 5, then there are 5+4+3+2+1=15 balls in total. Given the number 15, how would you figure out that the original x was 5?

I was a bit of a whiz back then and waded in to the problem. About 5 minutes later, I had an answer - but it was for the other way around - given x, I could figure out y with a simple formula:

y=x((x+1)/2)

So, given x=5, y=5((5+1)/2), y=15.

The teacher was a bit surprised at this. After all, I was about 12 years old at the time.

It didn’t solve the problem as it was asked, though.

All through secondary school, I tried reversing the formula to put it in terms of y instead of x. I didn’t succeed until only recently:

y=x((x+1)/2)
2y=x2+x
2y=(x+1/2)(x+1/2)-1/4 <-- this step only occurred to me a few weeks ago
2y+1/4=(x+1/2)2
(2y+1/4)1/2-1/2=x

How a primary school student was supposed to guess that formula, I have no idea!

To test, we plug in the 15 Y example we had:

(2*15+1.4)1/2-1/2=x
30.251/2-.5=x
5.5-.5=x
x=5

Success, but not pretty!

There /is/ a way of doing it which doesn’t involve quite as much maths.

First, you imagine how the triangle looks:

    O
   O O
  O O O
 O O O O
O O O O O

Nothing obvious yet… But, shift all the levels over to the left:

O
O O
O O O
O O O O
O O O O O

Now, it is obvious that the triangle is half of a square.

It’s not /exactly/ half, but it’s close enough that you can easily figure out x by getting the square root of 2y, then rounding down.

x = Floor[2y1/2]

I am almost certain that that’s the method that my teacher expected us to come up with. Took me 15 minutes to figure out the original formula, and 18 years to notice the much more obvious way to do it.