How computer memory works - Kanawat Senanan

翻译人员: Sophie Anderson 校对人员: Wu Di

In many ways, our memories make us who we are,

在许多方面来说，记忆决定了我们是什么样的人

helping us remember our past,

让我们不忘往事

learn and retain skills,

学习并记住新本领

and plan for the future.

以及为未来做规划

And for the computers that often act as extensions of ourselves,

像计算机常常扮演人的延伸这一角色

memory plays much the same role,

内存也起着同样的作用

whether it's a two-hour movie,

不论是一部两个小时的电影

a two-word text file,

写着两个单词的文本

or the instructions for opening either,

或是执行把两者都打开的指令

everything in a computer's memory takes the form of basic units called bits,

所有在计算机内存里的东西 都采以基本单位“比特”的这一形式出现

or binary digits.

我们也称之为二进制数字

Each of these is stored in a memory cell

每个二进制数被存放于存储元件中

that can switch between two states for two possible values,

在两种可能值间自如转换

0 and 1.

0和1

Files and programs consist of millions of these bits,

由数百万计的二进制数组成的程序和文件

all processed in the central processing unit,

在中央处理器中统一处理

or CPU,

也就是CPU

that acts as the computer's brain.

它担任计算机大脑一职

并且，随着要处理的二进制数成倍增长

And as the number of bits needing to be processed grows exponentially,

computer designers face a constant struggle

电脑设计师不断面临着

between size, cost, and speed.

有关数据大小、成本费用和处理速度三方面的难题

Like us, computers have short-term memory for immediate tasks,

和我们一样，电脑对于即时任务 有着短期记忆

and long-term memory for more permanent storage.

也有更为长久的固定储存器来保留长期记忆

When you run a program,

当你运行某个程序时

your operating system allocates area within the short-term memory

操作系统位于短期记忆的区域内

for performing those instructions.

以便践行指令

For example, when you press a key in a word processor,

打比方说，当你在文字处理软件中 按下一个键

the CPU will access one of these locations to retrieve bits of data.

中央处理器会访问其中一个位置 来检索这些数据

It could also modify them, or create new ones.

它也可以进行修改 或是产生新的数据

The time this takes is known as the memory's latency.

这个过程所花费的时间被称为延时

And because program instructions must be processed quickly and continuously,

由于程序指令必须处理迅速并且不断进行

all locations within the short-term memory can be accessed in any order,

短期记忆区的所有定位点以任意顺序被访问

hence the name random access memory.

因此又名随机访问存储器

The most common type of RAM is dynamic RAM, or DRAM.

最常见的随机储存器是动态随机存储器 或者说DRAM

There, each memory cell consists of a tiny transistor and a capacitor

在动态储存器中 每个储存单元由微小的晶体管和电容器组成

that store electrical charges,

用以贮存电荷

a 0 when there's no charge, or a 1 when charged.

0代表没有电 有电则是1

Such memory is called dynamic

我们称之为动态记忆的原因是

because it only holds charges briefly before they leak away,

它仅是在电荷耗散前 短暂保留它们

requiring periodic recharging to retain data.

需要定期充电来保留这些数据

But even its low latency of 100 nanoseconds

但即使是100纳秒的低延迟

is too long for modern CPUs,

对于现代CPU来说都算是高延迟了

so there's also a small, high-speed internal memory cache

因此“内部快取记忆体”应运而生

made from static RAM.

也就是静态随机存取存储器

That's usually made up of six interlocked transistors

它通常以六个联结晶状体所构成

which don't need refreshing.

不需要去更新

SRAM is the fastest memory in a computer system,

静态随机存取储存器是计算机系统中最快的存储器

but also the most expensive,

但也是最贵的

and takes up three times more space than DRAM.

也占用了比动态随机存取储存器多三倍的空间

But RAM and cache can only hold data as long as they're powered.

但是RAM和高速缓冲存储器只有充电后才能保存数据

For data to remain once the device is turned off,

为了保留数据 设备一旦关机后

it must be transferred into a long-term storage device,

必须将之转移到长期储存设备中

which comes in three major types.

这样的储存设备主要有三种类型

In magnetic storage, which is the cheapest,

在磁存储器，也就是三者中最便宜的储存设备中

data is stored as a magnetic pattern on a spinning disc coated with magnetic film.

数据以磁性模式 储存于磁膜编码的旋转盘上

But because the disc must rotate to where the data is located

但正因圆盘必须转到数据所位于的地方

in order to be read,

才能让它们被读取

the latency for such drives is 100,000 times slower than that of DRAM.

所以磁储存器的延时比DRAM慢上100,000倍

On the other hand, optical-based storage like DVD and Blu-ray

另一方面，像DVD和蓝牙这样的光储存设备

also uses spinning discs,

同样也使用旋转盘

but with a reflective coating.

只不过多了一层反射涂层

Bits are encoded as light and dark spots using a dye that can be read by a laser.

二进制数字被编译成空白点和黑点 加以涂料方便被激光识别读取

While optical storage media are cheap and removable,

尽管光储存媒体价钱便宜并可摘除

they have even slower latencies than magnetic storage

它们甚至比磁存储器有着更低的延时

and lower capacity as well.

同样也有着更小的容量

Finally, the newest and fastest types of long-term storage are solid-state drives,

末了，固态硬盘 是最新也是最快捷的长期存储器

like flash sticks.

比如闪存存储器

These have no moving parts,

它没有可运转的部件

instead using floating gate transistors

而是使用浮栅晶体管

that store bits by trapping or removing electrical charges

在他人专门设计的内部构件中

within their specially designed internal structures.

以捕获和排除电荷存储二进制数字

So how reliable are these billions of bits?

那么，这数十亿的二进制数字可靠性到底如何

We tend to think of computer memory as stable and permanent,

我们总认为 计算机存储器具有稳定性和永久性

but it actually degrades fairly quickly.

但实际上它降解得相当快

The heat generated from a device and its environment

由装置和周身环境所产生的热

will eventually demagnetize hard drives,

会使硬盘去磁

degrade the dye in optical media,

降解光学媒体内的染料

and cause charge leakage in floating gates.

并造成浮置栅极里的电荷流失

Solid-state drives also have an additional weakness.

固态硬盘也有额外的缺陷

Repeatedly writing to floating gate transistors corrodes them,

在不断重复存盘到浮栅中的过程中 晶体管会腐蚀固态硬盘

eventually rendering them useless.

使之毫无用处

With data on most current storage media

当今大多存储媒体内的数据

having less than a ten-year life expectancy,

寿命预测也不超过10年

scientists are working to exploit the physical properties of materials

科学家们正在尝试开拓材料的物理性能

down to the quantum level

将它们下至量子水平

in the hopes of making memory devices faster,

希望能因此制造出更快

smaller,

更小

以及更耐久的设备

and more durable.

For now, immortality remains out of reach, for humans and computers alike.

眼下，不朽仍无法实现 不论对于人类还是电脑而言