High memory

High Memory is the part of physical memory in a computer which is not directly mapped by the page tables of its operating system kernel. The phrase is also sometimes used as shorthand for the High Memory Area, which is a different concept entirely.

Some operating system kernels, such as Linux, divide their virtual address space into two regions, devoting the larger to user space and the smaller to the kernel. In current 32-bit x86 computers, this commonly (although does not have to, as this is a configurable option) takes the form of a 3GB/1GB split of the 4GB address space, so kernel virtual addresses start at 0xC0000000 and go to 0xFFFFFFFF. The lower 896 MB, from 0xC0000000 to 0xF7FFFFFF, is directly mapped to the kernel physical address space, and the remaining 128 MB, from 0xF8000000 to 0xFFFFFFFF, is used on demand by the kernel to be mapped to high memory. When in user mode, translations are only effective for the first region, thus protecting the kernel from user programs, but when in kernel mode, translations are effective for both regions, thus giving the kernel an easy way to refer to the buffers of processes—it just uses the process' own mappings.

词汇	High memory
分类	英语词汇英语翻译词典
释义	High memory 原声例句两分钟论文 Typically, in a maturing field, new techniques introduce a different kind of trade-off, for instance, less execution time but at the cost of higher memory consumption is a classical case. 通常来说，在一个成熟的领域，新技术总是会引入一种不同的折中方法，比如更少的执行时间，但是代价是更高的内存消耗，这是一种典型的情况。英语百科 High memory High Memory is the part of physical memory in a computer which is not directly mapped by the page tables of its operating system kernel. The phrase is also sometimes used as shorthand for the High Memory Area, which is a different concept entirely. Some operating system kernels, such as Linux, divide their virtual address space into two regions, devoting the larger to user space and the smaller to the kernel. In current 32-bit x86 computers, this commonly (although does not have to, as this is a configurable option) takes the form of a 3GB/1GB split of the 4GB address space, so kernel virtual addresses start at 0xC0000000 and go to 0xFFFFFFFF. The lower 896 MB, from 0xC0000000 to 0xF7FFFFFF, is directly mapped to the kernel physical address space, and the remaining 128 MB, from 0xF8000000 to 0xFFFFFFFF, is used on demand by the kernel to be mapped to high memory. When in user mode, translations are only effective for the first region, thus protecting the kernel from user programs, but when in kernel mode, translations are effective for both regions, thus giving the kernel an easy way to refer to the buffers of processes—it just uses the process' own mappings.
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