某些层次负责的是对下层不同实现的抽象，从而对上层屏蔽实现细节。比方说 VFS 对上层（系统调用层）来说提供了统一的调用接口，同时对下层中不同的文件系统规约了实现模型，当新增一种文件系统实现的时候，只需要按照这种模型来设计，就可以无缝插入到 Linux 文件系统中

缓存技术蕴含的是空间换时间的思想；压缩体现的是时间换空间的思想；分布式思想也最初体现在 CPU 的设计和实现上

普通磁盘的寻道时间是 10ms 左右，而相比于磁盘寻道花费的时间，CPU 执行指令和内存寻址的时间都在是 ns（纳秒）级别，从千兆网卡上读取数据的时间是在μs（微秒）级别

分层架构可以让我们更容易做横向扩展。如果系统没有分层，当流量增加时我们需要针对整体系统来做扩展。但是，如果我们按照上面提到的三层架构将系统分层后，那么我们就可以针对具体的问题来做细致的扩展

分层架构需要考虑的另一个因素，是层次之间一定是相邻层互相依赖，数据的流转也只能在相邻的两层之间流转

Happens-Before 并不是说前面一个操作发生在后续操作的前面，它真正要表达的是：前面一个操作的结果对后续操作是可见的

导致可见性的原因是缓存，导致有序性的原因是编译优化，那解决可见性、有序性最直接的办法就是禁用缓存和编译优化

Java 内存模型在 1.5 版本对 volatile 语义进行了增强。怎么增强的呢？答案是一项 Happens-Before 规则

Java 内存模型规范了 JVM 如何提供按需禁用缓存和编译优化的方法

final 修饰变量时，初衷是告诉编译器：这个变量生而不变，可以可劲儿优化

“同一时刻只有一个线程执行”这个条件非常重要，我们称之为互斥。如果我们能够保证对共享变量的修改是互斥的，那么，无论是单核 CPU 还是多核 CPU，就都能保证原子性了。

一个或者多个操作在 CPU 执行的过程中不被中断的特性，称为“原子性”

使用 watch 选项允许我们执行异步操作 (访问一个 API)，限制我们执行该操作的频率，并在我们得到最终结果前，设置中间状态。这些都是计算属性无法做到的

如果 <navigation-link> 没有包含一个 <slot> 元素，则该组件起始标签和结束标签之间的任何内容都会被抛弃。

计算属性是基于它们的响应式依赖进行缓存的。只在相关响应式依赖发生改变时它们才会重新求值。这就意味着只要 message 还没有发生改变，多次访问 reversedMessage 计算属性会立即返回之前的计算结果，而不必再次执行函数

组件是可复用的 Vue 实例，所以它们与 new Vue 接收相同的选项，例如 data、computed、watch、methods 以及生命周期钩子等。仅有的例外是像 el 这样根实例特有的选项

Roman Polanski is a man who cares deeply about his art and its place in this world. What happened to him on his incredible path is filled with tragedy, and most men would have collapsed. Instead, he became a great artist and continues to make great films.

In law, nothing is certain but the expense.

The U.S. Forces are winning in Iraq. It is to be hoped that they will win at home also.

It's a great thing to live in a digital age. It's convenient; it's fast.

I don't like family stories forcefully mixed with commercial elements.

In the '70s, everybody thought drugs were just good times. People didn't really know about drug addiction, or that such a thing existed. When I grew up in the '70s I thought you had to take drugs. It was almost like I didn't think you had a choice.

Labor Day is seen as a day of rest for many hardworking Americans.

We believed in our idea - a family park where parents and children could have fun- together.

Charm the quality in others that makes us more satisfied with ourselves.

Most of the debates I've participated in have been on Christian college campuses or on secular campuses; so, largely before a student audience.

Really, all I worry about is the work in hand.

Life is constantly supporting us and giving us gifts. It's a matter of opening ourselves to that.

But I think the - what the tea party movement demonstrates, and I think the, the, the enthusiasm that we're seeing from independents and Republicans, is that if Washington isn't going to change itself, then we're going to change Washington. And I think that's what we're seeing.

We cannot afford the creeping paralysis that destroys the effective will of democracy - the paralysis carried by hate and rancor, between class and class, person and person, party and party, as plague is carried through the streets of a town.

When I was 12, all I wanted for Christmas was a trampoline or a four-wheeler. I ended up getting both presents for Christmas.

It's time for Haitians to have access to health care. It's time to open our borders to the Haitian diaspora, open our markets to the world. It's time to open our country to potential investors.

A seventeenth-century house tends to be short on frills like hallways and closets; you must improvise.

If you're not being pessimistic, you're not being very realistic. But I think one must always have hope, and when you have children, of course, you have no choice but to work your tail off to try and protect the future for your children. And that is infused by hope in the end.

I feel good now. I've gained all my weight back after getting stoned for three weeks and not eating and not sleeping much. I've been coming by my mom's and eating food.

Let me be absolutely clear: I think it is defeatist to sort of say we want to leave the European Union. We're going to try and change the rules and change the way it works and change the objectives that it has in order to make it something that works for Britain.

As Congress debates overhauling the nation's health care system, it should not authorize a reform plan that would further our financial woes. We must avoid creating an unsustainable government program. There is no question that reform is needed, but health care can be made more affordable without massive and expensive new bureaucracies.

The extreme form of passionate love is secret love.

Comics, for me, is being able to sing alone in the shower. I find it freeing. You just pick up a pen and get to it.

Rich kids work hard. Most black kids aren't working hard enough.