Almost all computer processors these days usually come with a separate L1 or Level 1 cache and it is typically divided into two parts, data cache and instruction cache.
These two caches are used as two separate banks, one for storing the data and the other for storing the instructions.
In reality, there is not much difference between the data cache and the instruction cache apart from that apparently.
However, taking a closer look at the technicalities behind them, there are a few other differences that are quite evident.
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KEY TAKEAWAYS
- The data cache is designed to store the data while the instruction cache is designed to store instructions in it.
- The instruction cache is less associative and can run at the same speed of the CPU to offer single latency.
- The memory stage in the data cache is wired but in the instruction cache the fetch stage is wired.
7 Differences Between Data Cache and Instruction Cache
1. Purpose
The data cache is specifically designed to store data exclusively while the instruction cache, on the other hand, is exclusively used to store the instructions.
2. Coherence
In a few specific types of architectures, the instruction cache may not be as coherent as the data cache.
3. Economic Aspect
The instruction cache is comparatively cheaper in comparison to the data cache because it does not need memory coherence or to handle lookups for the storage.
On the other hand, the data cache is not so economic in that particular sense.
4. Stages Wired
In the data cache, typically, the memory stage is wired.
However, in comparison, it is the fetch stage that is wired to the instruction cache.
5. Associative Nature
The data cache is more associative in nature in comparison to the instruction cache.
On the other hand, the instruction cache is less associative in nature because it is made quite simpler and smaller in order to make it able to operate at the same speed as the Central Processing Unit or the CPU to ensure single cycle latency.
6. Inclusions
The data cache usually includes the cache lines that are fetched from the memory for the purpose of loading them into the register as data.
On the other hand, the instruction cache would typically include the cache lines that are typically fetched for execution from the memory.
7. Allocation
When and if the decode unit finds out that the data is a store or load, it passes the control over to the Load-Store unit and the data is then allocated to or retrieved from the data cache.
On the other hand, any data that is fetched on the basis of the address from the computer is allocated in the instruction cache by default since it is considered to be an instruction.
Which One is Necessary – Data Cache or Instruction Cache?
As it is evident from the list of differences between a data cache and an instruction cache above, it is pretty hard to say that the data cache eclipses the instruction cache in any or many aspects, and vice versa.
Therefore, the simple answer to your question is: none of them are. Typically, both data cache and instruction cache are necessary for a better performance of the CPU and the computer system overall.
It is true that the instruction cache in the software needs to be disabled when a user wants to create a code on the fly in order to make it work.
Still, the importance of this cache simply cannot be or should not be overlooked. And, there are lots of reasons to say so.
Generally speaking, both data and instructions have and follow a different pattern to access the memory.
Also, they both have to access different regions of it.
This means that if a computer system or a CPU, to be more precise, comes with the same cache for both data and instructions, it may not always work out well.
Therefore, it is so common to have two separate caches – a data cache that will be dedicated for storing the data only and an instruction cache that will be solely responsible for storing the varied types of instructions.
The modern processors are designed to rely heavily on faster caches while operating simply due to the reason that the main system memory or RAM is located far away and therefore results in much slower access.
Therefore, it is extremely necessary to have two separate caches which will invariably and effectively meet with the growing demand of the modern processors that need to run really fast.
As a result, a significant factor of the performance of the modern processors, which needs to be at a constant high level, is their heavy reliance on distinct pools of memory for instruction and data.
This is irrespective of the fact that the implementation details of it are quite complex.
So, it makes a lot of sense and provides a lot of logic to have separate data cache and instruction cache in the CPU design. Ideally, the Level 1 cache is divided into data and instruction cache.
Here the data cache cannot have both data and instructions especially, if you are not reading a part of a code as data.
On the other hand, the instruction cache cannot update copies of instructions written in a stream immediately.
And, when you consider the Level 2 and Level 3 caches, they will usually be shared and unified and may store both data and instructions.
Therefore, with all that said and explained, it can be concluded that separating the cache into two distinct parts will allow simultaneous access to the memory as and when required between the memory stage and instruction fetch stage of the CPU.
This will offer much higher bandwidth which is extremely important for the pipelined processors that are made these days to perform well.
Therefore, functionally speaking, the instruction cache, which is in no way different from any other type of CPU cache, along with the data cache are both typical and strict performance requirements for the modern process.
Conclusion
So, as you can see, there is not much difference between the data cache and the instruction cache but that does not mean your computer will perform well by using only one of them.
The article must have made clear the specific reasons for it to you.