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For example, an 8-bit-byte-addressable machine with a 20-bit address bus (e.g. Intel 8086) can address 2 20 (1,048,576) memory locations, or one MiB of memory, while a 32-bit bus (e.g. Intel 80386) addresses 2 32 (4,294,967,296) locations, or a 4 GiB address space. In contrast, a 36-bit word-addressable machine with an 18-bit address bus ...
The 1 MB total address space was a result of the 20-bit address space limit imposed on the 8088 CPU. Using the color video buffer space, some third-party utilities could add memory at the top of the 640k conventional memory area, to extend memory up to the base address used by hardware adapters. This could ultimately backfill RAM up to the MDA ...
The Commodore 128, and other 8-bit systems, meaning still with 16-bit addressing, could use more than 64 KB, i.e. 128 KB RAM, also the BBC Master with it expandable to 512 KB of RAM. While in general 8-bit CPUs have 16-bit addressing, in some architectures you have both, such as in the MOS Technology 6502 CPU, where the zero page is used ...
The most common word size is 8 bits, meaning that a single byte can be read or written to each of 2 m different words within the SRAM chip. Several common SRAM chips have 11 address lines (thus a capacity of 2 11 = 2,048 = 2k words) and an 8-bit word, so they are referred to as 2k × 8 SRAM.
An eight-bit processor like the Intel 8008 addresses eight bits, but as this is the full width of the accumulator and other registers, this could be considered either byte-addressable or word-addressable. 32-bit x86 processors, which address memory in 8-bit units but have 32-bit general-purpose registers and can operate on 32-bit items with a ...
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 address space. On the 8088, these address accesses were wrapped around to the beginning of ...
Internal RAM (IRAM) has an 8-bit address space, using addresses 0 through 0xFF. IRAM from 0x00 to 0x7F contains 128 directly addressable 1-byte registers, which can be accessed using an 8-bit absolute address that is part of the instruction.
An iconic example of virtual-to-physical address translation is virtual memory, where different pages of virtual address space map either to page file or to main memory physical address space. It is possible that several numerically different virtual addresses all refer to one physical address and hence to the same physical byte of RAM.