FreeBSD 内存问题

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FreeBSD 8.1-STABLE #0: Wed Aug 11 11:28:40 CST 2010
    [email protected]:/usr/obj/usr/src/sys/FW i386
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Intel(R) Xeon(R) CPU            3050  @ 2.13GHz (2133.42-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0x6f2  Family = 6  Model = f  Stepping = 2
  Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
  Features2=0xe3bd<SSE3,DTES64,MON,DS_CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM>
  AMD Features=0x20100000<NX,LM>
  AMD Features2=0x1<LAHF>
  TSC: P-state invariant
real memory  = 1073741824 (1024 MB)
avail memory = 251969536 (240 MB)
ACPI APIC Table: <DELL   PE_SC3  >
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
FreeBSD/SMP: 1 package(s) x 2 core(s)


为啥实际内存有1G，可是有效地怎么才240M？


top 命令查看的时候如下：

last pid:  1033;  load averages:  0.00,  0.00,  0.00    up 0+00:26:28  12:52:10
22 processes:  1 running, 21 sleeping
CPU:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
Mem: 8060K Active, 6208K Inact, 21M Wired, 36K Cache, 9584K Buf, 207M Free
Swap: 2048M Total, 2048M Free

是不是BIOS里有啥设置不对？或者有显卡之类的占用内存当显存了？或者BIOS太老需要更新一下？