課本 51 頁寫:
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. ...
套色框又寫:
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).
想問的問題是:
1. CS, SS, DS 不都只有 16-bit, 那到底是怎麼表示 segment? 是指說 CS 會連到一個
像 000000000040---- 的 GDT 去嗎? 還是說他本身存的是 base address 的部份?
2. limit field 是 16-bit or 20-bit 還是可以隨便指定? 不然為什麼圖例是 0400h
但套色框的可以是 10000h?
3. limit field value is implicitly multiplied by 1000 hex. Why 1000h? 那麼
一個 segment 能表示的最大範圍究竟是多大?
煩請助教幫忙解惑 謝謝
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