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计算机内存是怎样工作的? – 译学馆
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计算机内存是怎样工作的?

How computer memory works - Kanawat Senanan

在许多方面来说 记忆决定了我们是什么样的人
In many ways, our memories make us who we are,
让我们不忘往事
helping us remember our past,
学习并记住新本领
learn and retain skills,
以及为未来做规划
and plan for the future.
像计算机常常扮演人的延伸这一角色
And for the computers that often act as extensions of ourselves,
内存也起着同样的作用
memory plays much the same role,
不论是一部两个小时的电影
whether it’s a two-hour movie,
写着两个单词的文本
a two-word text file,
或是执行把两者都打开的指令
or the instructions for opening either,
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
everything in a computer’s memory takes the form of basic units called bits,
我们也称之为二进制数字
or binary digits.
每个二进制数被存放于存储元件中
Each of these is stored in a memory cell
在两种可能值间自如转换
that can switch between two states for two possible values,
0和1
0 and 1.
由数百万计的二进制数组成的程序和文件
Files and programs consist of millions of these bits,
在中央处理器中统一处理
all processed in the central processing unit,
也就是CPU
or CPU,
它担任计算机大脑一职
that acts as the computer’s brain.
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,
电脑设计师不断面临着
computer designers face a constant struggle
有关数据大小、成本费用和处理速度三方面的难题
between size, cost, and speed.
和我们一样 电脑对于即时任务有着短期记忆
Like us, computers have short-term memory for immediate tasks,
也有更为长久的固定储存器来保留长期记忆
and long-term memory for more permanent storage.
当你运行某个程序时
When you run a program,
操作系统位于短期记忆的区域内
your operating system allocates area within the short-term memory
以便践行指令
for performing those instructions.
打比方说 当你在文字处理软件中
For example, when you press a key in a word processor,
按下一个键中央处理器会访问其中一个位置
the CPU will access one of these locations to retrieve bits of data.
来检索这些数据 它也可以进行修改或是产生新的数据
It could also modify them, or create new ones.
这个过程所花费的时间被称为延时
The time this takes is known as the memory’s latency.
由于程序指令必须处理迅速并且不断进行
And because program instructions must be processed quickly and continuously,
短期记忆区的所有定位点以任意顺序被访问
all locations within the short-term memory can be accessed in any order,
因此又名随机访问存储器
hence the name random access memory.
最常见的随机储存器是动态随机存储器或者说DRAM
The most common type of RAM is dynamic RAM, or DRAM.
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
There, each memory cell consists of a tiny transistor and a capacitor
用以贮存电荷
that store electrical charges,
0代表没有电有电则是1
a 0 when there’s no charge, or a 1 when charged.
我们称之为动态记忆的原因是
Such memory is called dynamic
它仅是在电荷耗散前短暂保留它们
because it only holds charges briefly before they leak away,
需要定期充电来保留这些数据
requiring periodic recharging to retain data.
但即使是100纳秒的低延迟
But even its low latency of 100 nanoseconds
对于现代CPU来说都算是高延迟了
is too long for modern CPUs,
因此“内部快取记忆体”应运而生
so there’s also a small, high-speed internal memory cache
也就是静态随机存取存储器
made from static RAM.
它通常以六个联结晶状体所构成
That’s usually made up of six interlocked transistors
不需要去更新
which don’t need refreshing.
静态随机存取储存器是计算机系统中最快的存储器
SRAM is the fastest memory in a computer system,
但也是最贵的
but also the most expensive,
也占用了比动态随机存取储存器多三倍的空间
and takes up three times more space than DRAM.
但是RAM和高速缓冲存储器只有充电后才能保存数据
But RAM and cache can only hold data as long as they’re powered.
为了保留数据设备一旦关机后
For data to remain once the device is turned off,
必须将之转移到长期储存设备中
it must be transferred into a long-term storage device,
这样的储存设备主要有三种类型
which comes in three major types.
在磁存储器 也就是三者中最便宜的储存设备中
In magnetic storage, which is the cheapest,
数据以磁性模式储存于磁膜编码的旋转盘上
data is stored as a magnetic pattern on a spinning disc coated with magnetic film.
但正因圆盘必须转到数据所位于的地方
But because the disc must rotate to where the data is located
才能让它们被读取
in order to be read,
所以磁储存器的延时比DRAM慢上100 000倍
the latency for such drives is 100,000 times slower than that of DRAM.
另一方面 像DVD和蓝牙这样的光储存设备
On the other hand, optical-based storage like DVD and Blu-ray
同样也使用旋转盘
also uses spinning discs,
只不过多了一层反射涂层
but with a reflective coating.
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
Bits are encoded as light and dark spots using a dye that can be read by a laser.
尽管光储存媒体价钱便宜并可摘除
While optical storage media are cheap and removable,
它们甚至比磁存储器有着更低的延时
they have even slower latencies than magnetic storage
同样也有着更小的容量
and lower capacity as well.
末了 固态硬盘是最新也是最快捷的长期存储器
Finally, the newest and fastest types of long-term storage are solid-state drives,
比如闪存存储器
like flash sticks.
它没有可运转的部件
These have no moving parts,
而是使用浮栅晶体管
instead using floating gate transistors
在他人专门设计的内部构件中
that store bits by trapping or removing electrical charges
以捕获和排除电荷存储二进制数字
within their specially designed internal structures.
那么 这数十亿的二进制数字可靠性到底如何
So how reliable are these billions of bits?
我们总认为计算机存储器具有稳定性和永久性
We tend to think of computer memory as stable and permanent,
但实际上它降解得相当快
but it actually degrades fairly quickly.
由装置和周身环境所产生的热
The heat generated from a device and its environment
会使硬盘去磁
will eventually demagnetize hard drives,
降解光学媒体内的染料
degrade the dye in optical media,
并造成浮置栅极里的电荷流失
and cause charge leakage in floating gates.
固态硬盘也有额外的缺陷
Solid-state drives also have an additional weakness.
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
Repeatedly writing to floating gate transistors corrodes them,
使之毫无用处
eventually rendering them useless.
当今大多存储媒体内的数据
With data on most current storage media
寿命预测也不超过10年
having less than a ten-year life expectancy,
科学家们正在尝试开拓材料的物理性能
scientists are working to exploit the physical properties of materials
将它们下至量子水平
down to the quantum level
希望能因此制造出更快更小
in the hopes of making memory devices faster,
以及
smaller,
更耐久的设备
and more durable.
眼下 不朽仍无法实现不论对于人类还是电脑而言
For now, immortality remains out of reach, for humans and computers alike.

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