From the quote from Wikipedia, does "address translations" here mean the translation from virtual memory address to physical memory address?

Vector processors take this concept one step further. Instead of pipelining just the instructions, they also pipeline the data itself. The processor is fed instructions that say not just to add A to B, but to add all of the numbers "from here to here" to all of the numbers "from there to there". Instead of constantly having to decode instructions and then fetch the data needed to complete them, the processor reads a single instruction from memory, and it is simply implied in the definition of the instruction itself that the instruction will operate again on another item of data, at an address one increment larger than the last. This allows for significant savings in decoding time.

To illustrate what a difference this can make, consider the simple task of adding two groups of 10 numbers together. In a normal programming language one would write a "loop" that picked up each of the pairs of numbers in turn, and then added them. To the CPU, this would look something like this:

execute this loop 10 times
  read the next instruction and decode it
  fetch this number
  fetch that number
  add them
  put the result here
end loop

But to a vector processor, this task looks considerably different:

read instruction and decode it
fetch these 10 numbers
fetch those 10 numbers
add them
put the results here

There are several savings inherent in this approach. For one, only two address translations are needed. Depending on the architecture, this can represent a significant savings by itself. Another saving is fetching and decoding the instruction itself, which has to be done only one time instead of ten. The code itself is also smaller, which can lead to more efficient memory use.


1 Answer 1


Short answer: yes.

Long answer for the benefit of those who might not be familiar with the guts of a CPU:

In a modern architecture such as amd64, the CPU needs to take a virtual address that is basically an offset into a process's address space and map it into the raw (physical) address space - this is likely what you meant by virtual memory (not swap space).

This distinction is done both to simplify program code and to insulate userspace programs from each other. Back in the DOS days one rogue program could crash the whole operating system. Modern operating systems and CPUs prevent this by giving each program its own virtual sandbox to play in and closely guarding shared resources such as memory, hard disk, the network interface, etc.

  • Let's be more specific: this has nothing to do with CPU architecture and everything to do with the OS. The OS is responsible for managing virtual address translations (which may be hardware-assisted once configured). All CPUs can execute in a mode which permits direct access to physical memory - otherwise you could never boot up the OS needed to map those virtual pages.
    – nneonneo
    Feb 21, 2015 at 23:32
  • @nneonneo correct, modern desktop CPUs have multiple modes they can run in. However, protected mode is by far the most common for the reasons I outlined. I am not describing a theoretical issue but a practical one.
    – user22815
    Feb 21, 2015 at 23:33
  • You made it about the CPU architecture. I want to make it clear that this is not about the CPU architecture. It's about the OS. (Note that "protected mode" is a term very specific to x86-derived architectures; ARM, for example, has no such concept.)
    – nneonneo
    Feb 21, 2015 at 23:35
  • @nneonneo then what is the function of a MMU? If this is about the OS, why is the question talking about CPU instructions and pipelining?
    – user22815
    Feb 22, 2015 at 4:20

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