Introduction
I recently help some people who said ``I don't understand how to use my computer, but I want to do something.'' I found these people have interesting questions. So I write them that story here.What does it mean 8GB on my USB stick?
Some of my friends work on a social movement. They want to study something, they want to tell something to people and they want to discuss about it with others. For example, what is nationality of children when a couple married internationally? Are there any rights differing with others? They want to study these questions themselves. Usually it is deeply connected to their life.Here is a woman, who researched on a certain subject. She got a video materials and she wanted to share it with others. ``I don't know how to do that, but I want to show these materials to some people.'' This time I have a chance to help her. What she wanted was to show this video to around 30 people by a video projector.
She told me a compute is just a magic. However, she has a desktop computer and she can read and write emails. She can also browse the web pages. I thought that is enough. She can use a computer. If she told me, ``I can not type the keyboard,'' that would be hard. However, she has already had some knowledge. So we started.
First, we got a permission from the producer and the director to show it under some condition. Also she found a small place for 30 people with a video projector. One of her friends rents her a notebook computer, but it has no DVD drive. Her friend told her, ``you need a USB stick to hold the video.'' So the question was,
``I have 8GW stick, unused, does it work?''8GW? That's the power more than Kashiwazaki-Kariwa nuclear power plant, the largest nuclear power plant in the world. What on the earth does she have in her hand? It turned out 8GB. In German, W and B have somewhat similar pronunciation.
She told me, she has no idea, what these numbers and words, like what does GB means. She wanted to know it. I started explaining, but how much I should explain was not clear. There was a back and forth. At the end, the explanation was the following.
A computer usually stores information as `a file.' It originally means a paper file. It holds some papers to organize them. Computer uses this as an analogy to keep the information. A file in a computer has a size. The unit of size is called byte, written as 'B'.
One byte (1B) can hold roughly one Latin character information. If you need to remember 10 characters, then you need 10 bytes (10B). Computers only remember numbers, thus 1B storage actually holds a number. 1B can hold a number from 0 to 255. A typical Latin characters are: numbers ('0', '1', ..., '9'), small letters ('a', 'b', ..., 'z'), capital letters ('A', 'B', ..., 'Z'), symbols ('!', '#', '*', ...). 256 is enough large number to distinguish them. There are some tables that which number is corresponding to which character. The most widely used table is called ASCII (American Standard Code for Information Interchange. See https://en.wikipedia.org/wiki/ASCII). For instance, the character 'A' is represented by 65. (However, you see this method can only keep 256 kinds of characters and cannot hold Chinese or Japanese characters.)
Now you know what is `B' in 8GB. What is `G' after the 8? This `G' is called SI metric prefix (https://en.wikipedia.org/wiki/Metric_prefix). It represents a large number of a small number with a power of ten. SI stands for ``Le Système International d'Unités'' in French, it means a International Systems of Units. Does it sound too complicated? I believe you already know some of them. For example, a prefix represents 1000 is k, called kilo. One thousandths is m, called milli. (Actually a computer usually uses binary numbers, so it is 1024 instead of 1000 for kilo. However, I explain the system with decimal numbers here for simplicity. Let's learn one by one.)
Examples of SI prefixes.
| Multiples | Symbol | reading | Word origin |
|---|---|---|---|
l/1000000000
|
n
|
nano
|
``dwarf'' in Greek
|
1/1000000
|
μ
|
micro
|
``small'' in Greek
|
1/1000
|
m
|
milli
|
``thousandth'' in Latin
|
1
|
|||
1000
|
k
|
kilo
|
`thousand'' in Greek
|
1000000
|
M
|
Mega
|
`Great'' in Greek
|
1000000000
|
G
|
Giga
|
`Giant'' in Greek
|
1000000000000
|
T
|
Tera
|
`Monster'' in Greek
|
1KB means 1000B (in decimal). 1KB memory can store 1000 Latin characters. 1MB is a million B, and 1MB memory can store one million Latin characters.
These prefixes are based on Greek or Latin, so you can find related words. Sometime you can say something large things as Giga- or Mega-. There is a product called ``iPad nano.'' This means a small iPad. A small film is called microfilm. A small software company called Microsoft, ... no, this case, it is just a name. :-)
These k or M are prefixes and not only for B (byte). You can use them for other units, too. For example, m is a unit of length (meter). You can put k before m, km (kilometer). I don't see 1 Mm, still it should be valid. I don't know why I don't see 1Mm, it is usually written as 1000km. If you put a mass unit, g, 1000g is 1kg (kilogram). The unit of power is W (Watt), 1000W is 1kW, and 1000kW is 1MW.
Here is a rule of thumb of the size: a standard CD-ROM (compact disk read only memory) can hold approximately 650MB. A standard DVD-ROM (digital versatile disc read only memory) can hold 4.7GB. There are a few different format, so the size may differ, but there are good approximations. How long music or movie can these size hold? That actually depends on encoding/compression technology. Typically, a CD-ROM can hold 70 minutes sounds and a DVD-ROM can hold a two hours movie. Your computer's hard disk size is typically a few hundreds GB or a few TB in 2015.
The first question of my friend was ``I have 8GB stick, unused, does it work?'' (Here I fixed 8GW to 8GB.) If I know what is the size of her documentary movie files, then I can answer the question. She had 5 movie files, each of them is around 3 to 4 GB, but all of them are less than 4GB. They are 90 minutes to 120 minutes movie files. So, the answer is `No.' We need at least a 20GB USB stick if she wants to put all the movies in one USB stick.
I hope now you understand what the meaning of this three letters, 8GB. (I have not explained what is `8', but I think you know it.)
Summary
- I think you have an ability to use the computer if you can use emails and you can search on the web. I found some people just afraid a computer, but it is just a tool. Of course, you need some cautious to use a computer. But, you don't need to afraid of it. You can learn and understand it at some extent.
- How much information can a compute hold is measured by the unit B (byte). One byte can hold one Latin character.
- To express a large number or a small number easily, we use SI-prefixes. For example, 1,000 is represented by k (kilo), 1,000,000 is represented by M (mega).
- 8GB USB stick can hold around 8,000,000,000 Latin characters. This can usually hold two two hours movies.
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