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发表于 2005-8-7 16:35:19
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Post by 风雨纵横
又胡说了,32位机只能寻址 4 GB内存,物理无论你怎么操作系统都只能是4GB最多
CPU寻址,把32位地址编码放入EBX,ECX进行读取,这个是物理限制的,无论用什么操作系统都没用
所谓的超过 4 GB内存,是指swap+物理内存得到的,操作系统可以管理超大的swap
welans说的对, 寻址空间取决于地址总线数
物理地址扩展 (PAE) , 是intel Pentium Pro起引入的技术,它把原32根地址总线扩展到了36根.
HIGHMEM solution for using up to 4 GB of memory
Since Linux can't access memory which hasn't been directly mapped
into its address space, to use memory > 1 GB, the physical pages have
to be mapped in the kernel virtual address space first. This means
that the pages in ZONE_HIGHMEM have to be mapped in ZONE_NORMAL before
they can be accessed.
The reserved space which we talked about earlier (in case of x86, 128
MB) has an area in which pages from high memory are mapped into the
kernel address space.
To create a permanent mapping, the "kmap" function is used. Since this
function may sleep, it may not be used in interrupt context. Since the
number of permanent mappings is limited (if not, we could've directly
mapped all the high memory in the address space), pages mapped this
way should be "kunmap"ped when no longer needed.
Temporary mappings can be created via "kmap_atomic". This function
doesn't block, so it can be used in interrupt context. "kunmap_atomic"
un-maps the mapped high memory page. A temporary mapping is only
available as long as the next temporary mapping. However, since the
mapping and un-mapping functions also disable / enable preemption,
it's a bug to not kunmap_atomic a page mapped via kmap_atomic.
3. HIGHMEM solution for using 64 GB of memory
This is enabled via the PAE (Physical Address Extension) extension
of the PentiumPro processors. PAE addresses the 4 GB physical memory
limitation and is seen as Intel's answer to AMD 64-bit and AMD
x86-64. PAE allows processors to access physical memory up to 64 GB
(36 bits of address bus). However, since the virtual address space is
just 32 bits wide, each process can't grow beyond 4 GB. The mechanism
used to access memory from 4 GB to 64 GB is essentially the same as
that of accessing the 1 GB - 4 GB RAM via the HIGHMEM solution
discussed above.
还有
http://www.microsoft.com/whdc/sy ... ver/PAE/pae_os.mspx |
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发表于 2005-8-6 11:55:08