| 翻訳と辞書 |
| PCI memory hole ： ウィキペディア英語版 |
PCI hole
The PCI hole or PCI memory hole is a limitation of 32-bit hardware and 32-bit operating systems that causes a computer to appear to have less memory available than is physically installed. This memory addressing limitation and the later workarounds necessary to overcome it are functionally similar to the memory limits of the early 8088 IBM PC memory architecture (see Conventional memory).
Similar situations have often arisen in the history of computing, when hardware intended to have up to a certain level of resources is designed to handle several times the maximum expected amount, which eventually becomes a severe restriction as Moore's law increases resources economically available. The original IBM PC was typically supplied with 64 KB of memory or less; it was designed to take a maximum of 640 KB, far more than it was thought would ever be needed. In fact, Bill Gates is famously (but dubiously〔:wikiquote:Talk:Bill Gates〕) thought to have pointed out that "640 KB ought to be enough for anyone." This rapidly became a restriction that had to be handled by complex DOS memory management. Similar successive restrictions in size have been imposed and overcome on hard drives.
==Unavailable memory==
The loss of usable memory caused by the PCI hole, when using memory-mapped I/O, is caused by using the same address space for both physical memory and to communicate with hardware devices. Thus, installed hardware devices need some of the address space in order to communicate with the processor and system software. As 32-bit hardware has a total of four gigabytes of addressable memory, some of the real physical memory of a 32-bit machine, when enough memory is installed, needs to be sacrificed by making it hidden so the devices have room to communicate. Which part of physical memory becomes replaced with the device communication space depends upon the machine, but it is usually anything above 2.5 to 3.5 GB.
The amount of system memory that is hidden and unavailable varies widely with the actual mainboard and chipset, the BIOS, the amount of physical memory, the amount of video RAM installed on graphics cards, and the number and type of PCI cards installed in the system. More than a gigabyte of 32-bit system memory can be unavailable when four gigabytes of physical memory and multiple 3D cards with large amounts of video memory are installed; on some mainboards, the hole is always at least one gigabyte in size regardless of the installed expansion cards.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「PCI hole」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|