关于SuSE下E820显示的内存信息

yushang

<4> BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)    ＊
<4> BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
<4> BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
<4> BIOS-e820: 0000000000100000 - 000000001f7d0000 (usable)    ＊
<4> BIOS-e820: 000000001f7d0000 - 000000001f7e5600 (reserved)
<4> BIOS-e820: 000000001f7e5600 - 000000001f7f8000 (ACPI NVS)
<4> BIOS-e820: 000000001f7f8000 - 000000001f800000 (reserved)
<4> BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
<4> BIOS-e820: 00000000fed20000 - 00000000fed9b000 (reserved)
<4> BIOS-e820: 00000000feda0000 - 00000000fedc0000 (reserved)
<4> BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
<4> BIOS-e820: 00000000ffb00000 - 00000000ffc00000 (reserved)
<4> BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)
这是boot.msg中显示的物理内存的配置情况，我的机器配置了512M内存，
从这些信息里怎么才能看出来呢，为什么可用的内存这么少呢（标＊的）
才247M多一点，为什么？