This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "High memory" – news · newspapers · books · scholar · JSTOR(October 2012) (Learn how and when to remove this message)
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 4 GB 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.[1]
However, if the kernel needs to refer to physical memory for which a userspace translation has not already been provided, it has only 1 GB (for example) of virtual memory to use. On computers with a lot of physical memory, this can mean that there exists memory that the kernel cannot refer to directly—this is called high memory. When the kernel wishes to address high memory, it creates a mapping on the fly and destroys the mapping when done, which incurs a performance penalty.
High Bandwidth Memory (HBM) is a computer memory interface for 3D-stacked synchronous dynamic random-access memory (SDRAM) initially from Samsung, AMD...
Highmemory 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...
In DOS memory management, the highmemory area (HMA) is the RAM area consisting of the first 65520 bytes above the one megabyte in an IBM AT or compatible...
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time...
and manage them itself. DOS memory management Conventional memory Expanded memory (EMS) Highmemory area (HMA) Upper memory area (UMA) Global EMM Import...
main memory or primary storage. Archaic synonyms for main memory include core (for magnetic core memory) and store. Main memory operates at a high speed...
Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash...
Eidetic memory (/aɪˈdɛtɪk/ eye-DET-ik), also known as photographic memory and total recall, is the ability to recall an image from memory with high precision—at...
are the basis of "true" memory span. Though numerous factors affect memory span, the test is one that shows surprisingly high reliability. Results obtained...
physical memory in a machine could be organised as a combination of base or conventional memory (including lower memory), upper memory, highmemory (not the...
conventional memory by self-relocating resident drivers which move most of themselves into upper memory, the highmemory area, expanded or extended memory as well...
In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is...
small-form-factor version of the Memory Stick (including the PRO Duo); the even smaller Memory Stick Micro (M2), and the Memory Stick PRO-HG, a high speed variant of...
In computing, remote direct memory access (RDMA) is a direct memory access from the memory of one computer into that of another without involving either...
Synchronous Dynamic Random-Access Memory (DDR4 SDRAM) is a type of synchronous dynamic random-access memory with a high bandwidth ("double data rate") interface...
chips to need highmemory caches themselves. Internal storage Newer consoles have included internal storage devices, such as flash memory, hard disk drives...
flashbulb memory are a high level of surprise, a high level of consequentiality, and perhaps emotional arousal. The term flashbulb memory was coined...
Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices...
Memory segmentation is an operating system memory management technique of dividing a computer's primary memory into segments or sections. In a computer...
In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that...
Intel 80286 processors. It runs in real mode but can make use of the highmemory area. In addition to full Windows packages, there were runtime-only versions...
infrastructure, not shared by other tenants. HighMemory – Highmemory compute configurations to run memory-intensive applications. Shared Linodes – A balanced...
upper memory blocks (UMBs). The next stage in the evolution of DOS was for the operating system to use upper memory blocks (UMBs) and the highmemory area...
Memory management is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically...