How do hard drives work? - Kanawat Senanan

譯者: Shang-Yung Sun 審譯者: Max Chern

Imagine an airplane flying one millimeter above the ground

想像一架飛機在 離地一毫米的高度飛行

and circling the Earth once every 25 seconds

每 25 秒繞行地球一周

while counting every blade of grass.

同時細數地面上每一根小草

Shrink all that down so that it fits in the palm of your hand,

把這些縮小到你掌心大小

and you'd have something equivalent to a modern hard drive,

差不多即是現在的硬碟

an object that can likely hold more information than your local library.

一個比地方圖書館 可能保存更多資訊的物品

So how does it store so much information in such a small space?

以如此小的空間 是如何儲存這麼多的資料呢 ?

At the heart of every hard drive is a stack of high-speed spinning discs

每個硬碟的核心 是一疊高速旋轉的磁片

with a recording head flying over each surface.

磁片的每一面都有個 飛越其上的記錄磁頭

Each disc is coated with a film of microscopic magnetised metal grains,

每個磁片上都濺鍍一層 極微小的磁性金屬顆粒

and your data doesn't live there in a form you can recognize.

資料是以一種你無法辨識的形態存在

Instead, it is recorded as a magnetic pattern

事實上，資料是由那些成群的 細小顆粒所形成的磁化模式來記錄

formed by groups of those tiny grains.

In each group, also known as a bit,

每一個群組，也就是所謂的「位元」

all of the grains have their magnetization's aligned

所有的顆粒都有它們的磁化排列

in one of two possible states,

以兩種可能狀態之一呈現

which correspond to zeroes and ones.

也就是 0 和 1

Data is written onto the disc

數據寫入磁片中

by converting strings of bits into electrical current

是藉由通過電磁鐵 將一連串的位元轉換為電流

fed through an electromagnet.

This magnet generates a field strong enough to change the direction

這個電磁鐵產生一個強大的磁場

足以改變金屬顆粒的磁化方向

of the metal grain's magnetization.

Once this information is written onto the disc,

一旦資料被寫入磁片

the drive uses a magnetic reader to turn it back into a useful form,

磁碟機會用一個磁性的「讀頭」 將其轉換回可用的模式

much like a phonograph needle translates a record's grooves into music.

就像留聲機的唱針 將唱片紋路轉為音樂

But how can you get so much information out of just zeroes and ones?

但是怎樣從僅僅是 0 和 1 就能得到這麼多資訊呢？

Well, by putting lots of them together.

把它們湊在一起就可以了

For example, a letter is represented in one byte, or eight bits,

例如，用「1 位元組」 或「8 位元」表示一個字母

and your average photo takes up several megabytes,

你一般的照片是幾百萬位元組

each of which is 8 million bits.

一個「百萬位元組」是八百萬位元

Because each bit must be written onto a physical area of the disc,

因為每個位元 必須寫在磁片的實體位置上

we're always seeking to increase the disc's areal density,

所以我們總是致力於 增加磁片的儲存密度

or how many bits can be squeezed into one square inch.

或是在一平方英吋可以塞進多少位元

The areal density of a modern hard drive is about 600 gigabits per square inch,

現代硬碟的儲存密度差不多 是每平方英寸 6000 億位元

300 million times greater than that of IBM's first hard drive from 1957.

比 1957 年 IBM 的 第一個硬碟大 3 億倍

This amazing advance in storage capacity

這儲存容量上的大躍進

wasn't just a matter of making everything smaller,

並不只是把所有東西越做越小

but involved multiple innovations.

而是導入許多的創新

A technique called the thin film lithography process

一種稱為「薄膜微影技術」的製程

allowed engineers to shrink the reader and writer.

讓工程師們能將讀寫裝置縮小

And despite its size, the reader became more sensitive

儘管體積變小 讀頭卻變得更加靈敏

by taking advantage of new discoveries in magnetic and quantum properties of matter.

這全賴物質的磁性與 量子特性的新發現而獲益

Bits could also be packed closer together thanks to mathematical algorithms

位元也被壓縮地更密， 且拜數學演算法之賜

that filter out noise from magnetic interference,

能去除磁性干擾產生的雜訊

and find the most likely bit sequences from each chunk of read-back signal.

以及從每個回讀訊號 理出最有可能的位元排序

And thermal expansion control of the head,

而磁頭的熱膨脹控制

enabled by placing a heater under the magnetic writer,

是在磁性寫頭下方放置一個加熱器

allowed it to fly less than five nanometers above the disc's surface,

讓磁頭能以小於 5 奈米 的高度懸飛於磁碟上方

about the width of two strands of DNA.

差不多 2 串 DNA 的寬度

For the past several decades,

過去幾十年來

the exponential growth in computer storage capacity and processing power

電腦的儲存容量及處理能力呈指數式成長

has followed a pattern known as Moore's Law,

遵循 1975 年的「摩爾定律」模式的預測

which, in 1975, predicted that information density would double every two years.

亦即資訊密度每兩年將會倍增

But at around 100 gigabits per square inch,

但在每平方英吋 1000 億位元左右的密度

shrinking the magnetic grains further or cramming them closer together

若繼續縮小磁性顆粒或將它們排得更緊密

posed a new risk called the superparamagnetic effect.

會造成新的風險，稱為「超順磁性效應」

When a magnetic grain volume is too small,

當磁性顆粒體積太小

its magnetization is easily disturbed by heat energy

它的磁化很容易受熱能干擾

and can cause bits to switch unintentionally,

使得位元在無意中轉換方向

leading to data loss.

造成資料遺失

Scientists resolved this limitation in a remarkably simple way:

科學家們以非常簡單的方法 解決了這個限制：

by changing the direction of recording from longitudinal to perpendicular,

將記錄的方向由 「水平記錄」改成「垂直記錄」

allowing areal density to approach one terabit per square inch.

讓儲存密度提升到 每平方英吋 1 兆位元 ( 1 TB )

Recently, the potential limit has been increased yet again

最近又透過「熱輔助磁性記錄（HAMR）」 再度擴增其潛能

through heat assisted magnetic recording.

This uses an even more thermally stable recording medium,

這方法是使用一個 熱穩定性更好的記錄介質

whose magnetic resistance is momentarily reduced

在雷射加熱一個特定區域時 其磁阻會暫時減小

by heating up a particular spot with a laser

and allowing data to be written.

使資料得以寫入

And while those drives are currently in the prototype stage,

這種硬碟目前還只是在原型階段

scientists already have the next potential trick up their sleeves:

但科學家已經有下一個錦囊妙計了

bit-patterned media,

圖樣化磁紀錄技術 ( BPMR )

where bit locations are arranged in separate, nano-sized structures,

就是將數個位元排成 一個個奈米大小的圖樣結構

potentially allowing for areal densities of twenty terabits per square inch

可能使儲存密度提升到 每平方英吋 20 兆位元

or more.

甚至更多

So it's thanks to the combined efforts of generations of engineers,

總之，歸功於世世代代的工程師、

material scientists,

材料科學家

and quantum physicists

和量子物理學家的共同努力

that this tool of incredible power and precision

這既精密又能力超強的工具

can spin in the palm of your hand.

能運轉於你的手掌之中

翻譯：Shang-Yung Sun