[转译][马基 杰斯特(MarkeyJester) 摩托罗拉68000 入门教程] 壹 - 基础介绍 | 2. 内存存储
注意：本文经过原作者授权转译，转载请标明出处
原文地址：http://mrjester.hapisan.com/04_MC68/Sect01Part02/Index.html
条件允许建议阅读原文，网上非中文资料还是较多，当作锻炼英文岂不美哉
翻译若有不足之处欢迎批评指正
译文：
"如果有什么榨干了你，它一定是硬件" ---- 未知作者
简介
到目前为止，你应该对数据和不同的数据长度有了一定的基本概念，这里我们将康康数据到底存储在什么地方，以及它们是怎么被存储的
使用"偏移量" 来访问数据
计算机使用一种特殊的访问数据的方式，通过编址 (addressing)
| 偏移量 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00000000 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000010 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000030 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| ... |
上面这个表格是数据存储的一个例子，除了第一列和第一行之外的那些00 就是数据 (data) (即你的内存)，第一列和第一行的粗体数字就是偏移量
计算机会使用偏移量来作为地址 (address)，来定位内存中的它想要读取或者写入的某个字节。比如在下面这张表中，你会发现除了有一个例外，其他内存中的字节都是00：
| 偏移量 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00000000 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000010 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | F2 | 00 | 00 | 00 | 00 |
| 00000030 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| ... |
在B这一列的00000020行处的字节是F2，如果一台计算机想要读取这个字节，它将会用0000002B来作为寻找所用的偏移量，很简单吧？
那么让我们再康康更多的例子，比如下面这个在偏移量 00000013的位置：
| 偏移量 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00000000 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000010 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000030 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| ... |
如你所见在上面的表格里我们把00000010行的3列高亮了，以后所操作的偏移量我们都会高亮显示，现在让我们尝试把字 20 4F 写到0000000A 的位置：
| 偏移量 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00000000 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 20 | 4F | 00 | 00 | 00 | 00 |
| 00000010 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000030 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| ... |
你会发现，字 20 4F被分开了，20被放到了0000000A处，而4F则被放到了0000000B处
如果我们尝试从下面的内存的00000034处读取一个长字：
| 偏移量 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00000000 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000010 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| 00000030 | 00 | 00 | 00 | 00 | F3 | 44 | F5 | 39 | C2 | 00 | 00 | 00 | 00 | 00 | 00 | 00 |
| ... |
可以看到字节 F3，44，F5和39被高亮了，读取到的长字就是F3 44 F5 39，所以计算机不只是读取了00000034处的字节，它连着00000035，00000036和00000037都读取了，然后把它们拼在一起组成了一个长字
之后我们会更加详细和深入的讨论内存相关的话题，希望到现在为止你已经有了一些基本的认识
目录
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