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Die of AMD 8088. The 8088 was designed at Intel's laboratory in Haifa, Israel, as were a large number of Intel's processors. [9] The 8088 was targeted at economical systems by allowing the use of an eight-bit data path and eight-bit support and peripheral chips; complex circuit boards were still fairly cumbersome and expensive when it was released.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] ... The descriptor contains a memory address and a PCID. [ab]
This derived directly from the hardware design of the Intel 8086 (and, subsequently, the closely related 8088), which had exactly 20 address pins. (Both were packaged in 40-pin DIP packages; even with only 20 address lines, the address and data buses were multiplexed to fit all the address and data lines within the limited pin count.)
The Intel 8088 CPU, used in the original IBM PC, was able to address 1 MB (2 20 bytes), since the chip offered 20 address lines. In the design of the PC, the memory below 640 KB was for random-access memory on the motherboard or on expansion boards, and it was called the conventional memory area.
On the 8086, 8088, and 80186, the result of an effective address that overflows 20 bits is that the address "wraps around" to the zero end of the address range, i.e. it is taken modulo 2^20 (2^20 = 1048576 = 0x100000). However, the 80286 has 24 address bits and computes effective addresses to 24 bits even in real mode.
In computing, protected mode, also called protected virtual address mode, [1] is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
The Intel 8086, Intel 8088, and Intel 80186 processors had 20 address lines, numbered A0 to A19; with these, the processor can access 2 20 bytes, or 1 MB. Internal address registers of such processors only had 16 bits.
The Intel 8088 processor used in the original IBM PC had 20 address lines and so could directly address 1 MiB (2 20 bytes) of memory. Different areas of this address space were allocated to different kinds of memory used for different purposes.