Content deleted Content added
→End-of-address space quirkiness: copy edit/language correction: this not referring to a space that is about the "end of address", it is quirkiness about the "end of address space". |
→End-of-address-space quirkiness: This applies equally to 8086 and 8088 CPUs. |
||
Line 47:
=== End-of-address-space quirkiness ===
{{main article|A20 line}}
The last segment, FFFFh (65535), begins at linear address FFFF0h (1048560), 16 bytes before the end of the 20-bit address space, and thus can access, with an offset of up to 65,536 bytes, up to 65,520 (65536−16) bytes past the end of the 20-bit 8088 CPU's address space. A further 4,094 next-highest 64K-segments also still cross that 1MB-threshold, but by less and less. On the 8086 and 8088
In 16-bit real mode, enabling applications to make use of multiple memory segments (in order to access more memory than available in any one 64K-segment) is quite complex, but was viewed as a necessary evil for all but the smallest tools (which could do with less memory). The root of the problem is that no appropriate address-arithmetic instructions suitable for flat addressing of the entire memory range are available.{{Citation needed|date=July 2011}} Flat addressing is possible by applying multiple instructions, which however leads to slower programs.
| |||