这些单元与基准时间寄存器相同，并且两个线程的PURR值的总和等于基准时间寄存器的值。
The units are the same as the time base register and the sum of the PURR values for both threads is equal to time base register.
例如，编译器为了优化一个循环索引变量，可能会选择把它存储到一个寄存器中，或者缓存会延迟到一个更适合的时间，才把一个新的变量值存入主存。
For example, a compiler may choose to optimize a loop index variable by storing it in a register, or the cache may delay flushing a new value of a variable to main memory until a more opportune time.
有时，语义上等同但采用两种不同方式编写的代码可能会使优化器在执行良好的寄存器分配上所花费的时间相差巨大。
At times, semantically equivalent code, written in two different ways, might cause the optimizer to have a more difficult time performing good register allocation.
使用TB寄存器和systemcfg结构中的值，就可以按纳秒精度计算从UNIX纪元到现在经过的时间，方法如下。
Using the TB register and the values exposed in the systemcfg structure, elapsed time since the epoch with nanosecond precision can be calculated as.
执行过程中的一个阶段所需的时间，在此期间，计算机从主存储器中取出指令或操作数，并将其存入控制器或运算器的寄存器中。
The part of execution in which an operand or instruction is read from main storage and written into a control unit or arithmetic unit register.
中央处理器（CPU）读取寄存器并计算常驻及等待时间，该时间被写入到PTP后续包中。
The CPU reads the register and calculates residence and latency times that is entered in PTP follow up packets.
一般来说，内存层次结构如下的访问时间与快速的CPU寄存器顶部和缓慢的硬盘驱动器在底部。
Generally, the memory hierarchy follows the access time with the fast CPUregisters at the top and the slow hard drive at the bottom.
一般来说，内存层次结构如下的访问时间与快速的CPU寄存器顶部和缓慢的硬盘驱动器在底部。
Generally, the memory hierarchy follows the access time with the fast CPUregisters at the top and the slow hard drive at the bottom.
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