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A second prominent example is the set of microcode patches that Intel offered for some of their processor architectures of up to 10 years in age, in a bid to counter the security vulnerabilities discovered in their designs – Spectre and Meltdown – which went public at the start of 2018.
The processor boots up using a set of microcode held inside the processor and stored in an internal ROM. [1] A microcode update populates a separate SRAM and set of "match registers" that act as breakpoints within the microcode ROM, to allow jumping to the updated list of micro-operations in the SRAM. [ 1 ]
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 .
The XSAVE instruction set extensions are designed to save/restore CPU extended state (typically for the purpose of context switching) in a manner that can be extended to cover new instruction set extensions without the OS context-switching code needing to understand the specifics of the new extensions.
The MIC-1 is a CPU architecture invented by Andrew S. Tanenbaum to use as a simple but complete example in his teaching book Structured Computer Organization.. It consists of a very simple control unit that runs microcode from a 512-words store.
The source code for EIS/FIS microcode was included so these instructions, normally located in the third MICROM, could be loaded in the WCS, if desired. [ 11 ] Later Q-Bus based systems such as the LSI–11/23, /73, and /83 are based upon chip sets designed in house by Digital Equipment Corporation.
If <address> is hex xxFF (i.e., any word ending in FF), the processor will not jump to the address stored in xxFF and xxFF+1 as expected, but rather the one defined by xxFF and xx00 (for example, JMP ($10FF) would jump to the address stored in 10FF and 1000, instead of the one stored in 10FF and 1100). This can be avoided simply by not placing ...
Some microcoded CPU designs with a writable control store use it to allow the instruction set to be changed (for example, the Rekursiv processor and the Imsys Cjip). [19] CPUs designed for reconfigurable computing may use field-programmable gate arrays (FPGAs). An ISA can also be emulated in software by an interpreter. Naturally, due to the ...