作者chanwen (Te quiero!)
看板PangSir
标题[问题] Protected Mode Flat Segmentation Model
时间Wed Nov 3 22:35:57 2004
课本 51 页写:
Each segment is defined by a segment descriptor, a 64-bit value stored
in a table known as the global descriptor table (GDT). ... The segment li-
mit field can optionally indicate the amount of physical memory in the sys-
tem. In Figure 2-12, the segment limit is 0400. ...
套色框又写:
Suppose a computer had 256MB of RAM. The segment limit field would con-
tain 10000 hex because its value is implicitly multiplied by 1000 hex, pro-
ducing 10000000 hex (256MB).
想问的问题是:
1. CS, SS, DS 不都只有 16-bit, 那到底是怎麽表示 segment? 是指说 CS 会连到一个
像 000000000040---- 的 GDT 去吗? 还是说他本身存的是 base address 的部份?
2. limit field 是 16-bit or 20-bit 还是可以随便指定? 不然为什麽图例是 0400h
但套色框的可以是 10000h?
3. limit field value is implicitly multiplied by 1000 hex. Why 1000h? 那麽
一个 segment 能表示的最大范围究竟是多大?
烦请助教帮忙解惑 谢谢
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