Editing 1938: Meltdown and Spectre
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The phantom trolley driving through walls is an analogy for the computer instructions being able to access areas of memory that should be protected from them. This may also be a reference to {{w|quantum tunnelling}}, or even simply a joke about the phantom trolley being a literal phantom, i.e. incorporeal. | The phantom trolley driving through walls is an analogy for the computer instructions being able to access areas of memory that should be protected from them. This may also be a reference to {{w|quantum tunnelling}}, or even simply a joke about the phantom trolley being a literal phantom, i.e. incorporeal. | ||
− | In many cases, contrary to what the comic implies, both paths are not taken simultaneously during speculative execution. A {{w|branch predictor}} may be used to select the most likely path, and the effects should be completely erased if the predicted path is incorrect | + | In many cases, contrary to what the comic implies, both paths are not taken simultaneously during speculative execution. A {{w|branch predictor}} may be used to select the most likely path, and the effects should be completely erased if the predicted path is incorrect. Both branch prediction and taking both paths (known as eager evaluation) are considered speculative execution and are affected by these bugs. |
The {{w|Row hammer}} problem had been known for many years before this comic was published. A {{w|Dynamic random-access memory|common form of computer memory}} is constructed from tiny capacitors organized in a two-dimensional grid of rows and columns. Capacitors store charge to represent information. By applying a pattern of memory access that rapidly changes a row of capacitors, you can cause charge to overflow to nearby rows and incorrectly change their states. | The {{w|Row hammer}} problem had been known for many years before this comic was published. A {{w|Dynamic random-access memory|common form of computer memory}} is constructed from tiny capacitors organized in a two-dimensional grid of rows and columns. Capacitors store charge to represent information. By applying a pattern of memory access that rapidly changes a row of capacitors, you can cause charge to overflow to nearby rows and incorrectly change their states. |