His Story

分不清楚电脑系统里的家长控制(Parental Control)功能是用来让家长去控制 的，还是控制家长的。反正刚刚听同事说，他家小学快毕业的小孩用这个很牛B的功能把电脑加了密，然后他怎么也登陆不了。他本身就是搞技术开发，可就是没辙。

BTW，说到家长，今天是老妈五十岁生日。小时候不懂事，让您费心了。生日快乐！

Wow, that is a long title. Yes, they are the famous two principles in Software Engineering I’ve learned when I was in ITB. It says that, the software you designed is stable, if in general

1. It will never enter a undesired state
2. If it unfortunately enters an undesired state, it will eventually back to a desired state later.

While it is realistically impossible to achieve the first goal, although software engineers are trying to reach it as close as possible, there are many ways to accomplish the second one. It sometime can be some procedures, which are what we called "backup plans"; it sometime can be some kind of self recovery mechanism; or, it can be proved that the software will eventually do something good. Here is the video version of the idea.

……但是还是有很多神奇的东西。刚刚从邮箱里发现伊不远万里寄来的一个礼物，欣喜万分。

大家猜猜看这是个什么东西？

9/11 更新：

这个东西叫做i卡拉OK。只要接在水果牌的音乐播放器上，那个小孔出来的音乐就是消过原声的。然后对着另外一端唱歌，声音会自动融入消过原声的音乐里。上面那些按钮是调 key 的，所以不会有破音的机会。厉害吧？

It’s a nice sunny afternoon in the library. So I tried to start a video chat to share this sunshine with her. However, she denied my request. She said that there is a limit on the bandwidth of 1GB per week with the broadband network in her residence.

Bandwidth, is a measure of the amount of data that can be transferred between computers in a network within a specific period.

I’ve been thinking about this for a while: Why do the Internet service providers want to limit the bandwidth? Well, the most reason I’ve heard is that they want to protect the network device from being overloaded and avoid other network users from squeezed out of the information highway.

Hmm, how can they do that by limiting the bandwidth? Let’s take an example in real world. Say there is a bridge on a river and people walk through the bridge from one side to the other side every day. Unfortunately there is a policy from the bridge owner that the bandwidth, the number of times one person allowed to walk through the bridge, is 10 times per day. Sadly, most people need to use the bridge several times only in the morning. It turns out that there are about 100 people walking on the bridge and each person go back and forth 10 times during that time. They don’t really need the bridge for the rest of the day except in the morning. Bridge is overloaded and few guys with bad luck fell into the river because of that.

I think, what the bridge owner really mean, is to limit the throughput.

Throughput, is a measure of the amount of data that can be transferred in a time unit between computers in a network.

It means that, if I am the bridge owner, I don’t care how many time you walk through the bridge everyday. But you must follow the rule that you are allowed to using that bridge for at most twice per hour! So no one will be waiting by the entrance and the bridge is always is good shape.

It’s the same for the computer network. Why can’t they just limit the throughput to, say 256kb per second? Doesn’t that make more sense?