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Four registers are used to refer to four segments on the 16-bit x86 segmented memory architecture. DS (data segment), CS (code segment), SS (stack segment), and ES (extra segment). Another 16-bit register can act as an offset into a given segment, and so a logical address on this platform is written segment:offset, typically in hexadecimal ...
Some systems have a "split" memory architecture where machine code, constants, and data are in different locations, and may have different address sizes. For example, PIC18 microcontrollers have a 21-bit program counter to address machine code and constants in Flash memory, and 12-bit address registers to address data in SRAM.
Start monitoring a memory location for memory writes. The memory address to monitor is given by DS:AX/EAX/RAX. [m] ECX and EDX are reserved for extra extension and hint flags, respectively. [n] Usually 0 [o] Prescott, Yonah, Bonnell, K10, Nano: MWAIT [l] MWAIT EAX,ECX: NP 0F 01 C9: Wait for a write to a monitored memory location previously ...
In the original 8086 / 8088 / 80186 / 80188 every address was built from a segment register and one of the general purpose registers. For example ds:si is the notation for an address formed as [16 * ds + si] to allow 20-bit addressing rather than 16 bits, although this changed in later processors.
The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20- bit segmented memory address space (giving 1 MB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware.
The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 [citation needed] and June 8, 1978, when it was released. [5] The Intel 8088, released July 1, 1979, [6] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM ...
The V30 was a factory upgrade from the 8086 used in the GTD-5 EAX Class 5 central office switch. It was also used in the Psion Series 3 , the NEC PC-9801 VM, the Olivetti PCS86, the Applied Engineering "PC Transporter" card for the Apple II series of computers, and in various arcade machines (particularly ones made by Irem ) in the late 1980s.
Instructions included an address for the operand. For instance, an ADD address instruction would cause the CPU to retrieve the number in memory found at that address and then add it to the value already in the accumulator. This very simple example ISA has a "one-address format" because each instruction includes the address of the data. [4]