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In computer architecture, millicode is a higher level of microcode used to implement part of the instruction set of a computer. The instruction set for millicode is a subset of the machine's native instruction set, omitting those instructions that are implemented using millicode, plus instructions that provide access to hardware not accessible using the native instruction set.
Machine code is generally different from bytecode (also known as p-code), which is either executed by an interpreter or itself compiled into machine code for faster (direct) execution. An exception is when a processor is designed to use a particular bytecode directly as its machine code, such as is the case with Java processors .
As of October 30, 2009 there were fewer than 500 lines of Yod'm source remaining in the DeskSpace code base. On February 6, 2009, DeskSpace was reviewed on the BBC News ' Click ' television segment. [ 10 ]
[7] [8] Second generation languages represented a massive step away from the tradition of programmers conforming to the needs of a machine, and the first step towards the machine accommodating for the programmer, a phenomenon that would be repeated in all subsequent programming language generations. [2] [3]
Individual registers in the file are referred to by number in the machine code. Encoding a number in the machine code requires several bits. For instance, in the Zilog Z80 there were eight general-purpose registers in the file. To select one of eight values requires three bits, as 2 3 = 8. More registers in the file will result in better ...
In computer architecture, predication is a feature that provides an alternative to conditional transfer of control, as implemented by conditional branch machine instructions. Predication works by having conditional ( predicated ) non-branch instructions associated with a predicate , a Boolean value used by the instruction to control whether the ...
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.
The default OperandSize and AddressSize to use for each instruction is given by the D bit of the segment descriptor of the current code segment - D=0 makes both 16-bit, D=1 makes both 32-bit. Additionally, they can be overridden on a per-instruction basis with two new instruction prefixes that were introduced in the 80386: