operating-system - 是否有关于 'The Social Network'中询问的分页qn的解释？

Question

“假设您给计算机提供了16位虚拟地址，页面大小为256字节。系统使用从地址十六进制400开始的1级页面表。也许您想要DMA ...谁知道？前几个页面保留用于硬件标志等。假定页面表条目具有8个状态位。这8个状态位应为...”

http://www.youtube.com/watch?v=-3Rt2_9d7Jg

有人可以解释为什么答案是Mark/Jesse所描述的吗？

Answer 1

根据该页面记录的The Social Network的some technical inaccuracies，该问题(很严重)是从actual Harvard course的问题派生而来的。

A sample problem: Suppose we are given a computer with a 16-bit virtual addresses, and a page size of 256 bytes. The system uses one-level page tables, which start at address 0x0400. (The first few pages are reserved for hardware flags, etc. Maybe you wanted to have DMA on your 16-bit system, who knows?) Assume page table entries have eight status bits: 1 valid bit, 1 modify bit, 1 reference bit, and 5 permissions bits (this is a very secure system).

How many pages are there? How much memory do the page tables require?

这8个状态位取决于体系结构，在这个特定的问题中，被假定为虚拟计算机的假设。电影制片人只是简单地将问题描述作为问题的假设，而将其中一个假设设为问题-首先提出这个问题是没有道理的。

为了更容易理解这一点，请想象您有一个类似以下的问题

A car traveled across a road for 1 hour. Assuming the car's speed is 100km/h, how much distance did the car travel?

问题变成了

A car traveled across a road for 1 hour. The speed of the car was...?

编辑:没意识到原始文章使用了类似的类比。