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The IBM System/360 Model 91 was an early machine that supported out-of-order execution of instructions; it used the Tomasulo algorithm, which uses register renaming. The POWER1 from 1990 is the first microprocessor that used register renaming and out-of-order execution. This processor implemented register renaming only for floating-point loads.
Reservation station as part of Intel's Nehalem microarchitecture. A unified reservation station, also known as unified scheduler, is a decentralized feature of the microarchitecture of a CPU that allows for register renaming, and is used by the Tomasulo algorithm for dynamic instruction scheduling.
Tomasulo's algorithm uses register renaming to correctly perform out-of-order execution. All general-purpose and reservation station registers hold either a real value or a placeholder value. If a real value is unavailable to a destination register during the issue stage, a placeholder value is initially used.
On hardware where software pipelining is necessary to improve performance alongside loop unrolling (i.e. hardware which lacks register renaming or implements in-order superscalar execution), additional registers may need to be used to store temporary variables from multiple iterations that could otherwise reuse the same register. [7]
Example of a 4-window register window system. In computer engineering, register windows are a feature which dedicates registers to a subroutine by dynamically aliasing a subset of internal registers to fixed, programmer-visible registers. Register windows are implemented to improve the performance of a processor by reducing the number of stack ...
The rename command is supported by Tim Paterson's SCP 86-DOS. [26] On MS-DOS, the command is available in versions 1 and later. [27] DR DOS 6.0 also includes an implementation of the ren and rename commands. [28] In Windows PowerShell, ren is a predefined command alias for the Rename-Item Cmdlet which basically serves the same purpose. [29]
This same technique is used in the R10000 register renaming mapping file, which stores a 6-bit virtual register number for each of the physical registers. In the renaming file, the renaming state is checkpointed whenever a branch is taken, so that when a branch is detected to be mispredicted, the old renaming state can be recovered in a single ...
The 1967 IBM System/360 Model 91, was another early influence that introduced out-of-order execution, pioneering use of Tomasulo's algorithm. [3] The Intel i960 CA (1989), [ 4 ] the AMD 29000 -series 29050 (1990), and the Motorola MC88110 (1991), [ 5 ] microprocessors were the first commercial single-chip superscalar microprocessors.