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Cyrix Coma Bug
The Cyrix coma bug is a design flaw in Cyrix 6x86 (introduced in 1996), 6x86L, and early 6x86MX processors that allows a non-privileged program to hang the computer. Discovery According to Andrew Balsa, around the time of the discovery of the F00F bug on Intel Pentium, Serguei Shtyliov from Moscow found a flaw in a Cyrix processor while developing an IDE disk driver in assembly language. Alexandr Konosevich, from Omsk, further researched the bug and coauthored an article with Uwe Post in the German technology magazine ''c't'', calling it the "hidden CLI bug" (CLI is the instruction that disables interrupts in the x86 architecture). Balsa, as a member on the Linux kernel mailing list, confirmed that the following C program (which uses inline x86-specific assembly language) could be compiled and run by an unprivileged user: unsigned char c = ; int main() { asm ( " movl $c, %ebx\n" "again: xchgl (%ebx), %eax\n" " movl %eax, %edx\n" " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Design Flaw
''Design Flaw'' is the fifth studio album by Art Bergmann, released on the Other People's Music record label in 1998."Bergmann back to form". ''The Province'', November 6, 1998. The album featured acoustic recordings of songs, primarily from Bergmann's prior albums but also including a new Gram Parsons cover. ''Calgary Herald'' music critic James Muretich named the album as one of the year's best, writing that "one of our best singer-songwriters of the last 20 years brilliantly delves into his repertoire of songs dealing with desire, drugs and dreams.""Rufus heads up the tracks of '98: Canadian critics pick albums by Wainwright, Lucinda Williams as the year's best releases". ''Montreal Gazette ''The Gazette'', also known as the ''Montreal Gazette'', is a Canadian English-language broadsheet daily newspaper which is owned by Postmedia Network. It is published in Montreal, Quebec, Canada. It is the only English-language daily newspape ...'', December 26, 1998. Bergmann's nex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Interrupt
In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, the processor will suspend its current activities, save its state, and execute a function called an '' interrupt handler'' (or an ''interrupt service routine'', ISR) to deal with the event. This interruption is often temporary, allowing the software to resume normal activities after the interrupt handler finishes, although the interrupt could instead indicate a fatal error. Interrupts are commonly used by hardware devices to indicate electronic or physical state changes that require time-sensitive attention. Interrupts are also commonly used to implement computer multitasking and system calls, especially in real-time computing. Systems that use interrupts in these ways are said to be interrupt-driven. History Hardware interrupts wer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
NOP (code)
In computer science, a NOP, no-op, or NOOP (pronounced "no op"; short for no operation) is a machine language instruction and its assembly language mnemonic, programming language statement, or computer protocol command that does nothing. Machine language instructions Some computer instruction sets include an instruction whose purpose is to not change the state of any of the programmer-accessible registers, status flags, or memory. It often takes a well-defined number of clock cycles to execute. In other instruction sets, there is no explicit NOP instruction, but the assembly language mnemonic NOP represents an instruction which acts as a NOP; e.g., on the SPARC, sethi 0, %g0. A NOP must not access memory, as that could cause a memory fault or page fault. A NOP is most commonly used for timing purposes, to force memory alignment, to prevent hazards, to occupy a branch delay slot, to render void an existing instruction such as a jump, as a target of an execute i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Deadlock (computer Science)
In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lock. Deadlocks are a common problem in multiprocessing systems, parallel computing, and distributed systems, because in these contexts systems often use software or hardware locks to arbitrate shared resources and implement process synchronization. In an operating system, a deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process. If a process remains indefinitely unable to change its state because resources requested by it are being used by another process that itself is waiting, then the system is said to be in a deadlock. In a communications system, deadlocks occur mainly due to loss ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Branch Predictor
In computer architecture, a branch predictor is a digital circuit that tries to guess which way a branch (e.g., an if–then–else structure) will go before this is known definitively. The purpose of the branch predictor is to improve the flow in the instruction pipeline. Branch predictors play a critical role in achieving high performance in many modern pipelined microprocessor architectures. Two-way branching is usually implemented with a conditional jump instruction. A conditional jump can either be "taken" and jump to a different place in program memory, or it can be "not taken" and continue execution immediately after the conditional jump. It is not known for certain whether a conditional jump will be taken or not taken until the condition has been calculated and the conditional jump has passed the execution stage in the instruction pipeline (see fig. 1). Without branch prediction, the processor would have to wait until the conditional jump instruction has passed the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Instruction Pipeline
In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming Machine code, instructions into a series of sequential steps (the eponymous "Pipeline (computing), pipeline") performed by different Central processing unit#Structure and implementation, processor units with different parts of instructions processed in parallel. Concept and motivation In a pipelined computer, instructions flow through the central processing unit (CPU) in stages. For example, it might have one stage for each step of the von Neumann architecture, von Neumann cycle: Fetch the instruction, fetch the operands, do the instruction, write the results. A pipelined computer usually has "pipeline registers" after each stage. These store information from the instruction and calculations so that the logic gates of the next stage can do th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
