What is the expected growth rate for Rambus's SG&A expenses for the year
Seraphin -- Chief Executive Officer
Thanks, Sidney.
Operator
Your next question comes from the line of Mehdi Hosseini with SIG. Your line is open. You may ask your question.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
Yes, thanks for taking my question. Just want to follow up to Sidney's. And want to dig into silicon IP opportunities, especially with AI and machine learning. And this is something that, in my opinion, we're still in the early phase.
But I want to see how much of those incremental opportunities are part of your expectation? Or would this actually provide any upside to your overall opportunities for this year and beyond? And I have a follow-up.
Luc Seraphin -- Chief Executive Officer
Hi, Mehdi. The AI and ML opportunities do add potential revenue for our IP cores, especially HBM where we do show a very high-bandwidth capability, you know? AI is going to be consuming a large portion of the data center growth going forward. So anyone building a chip for AI that goes into data center will eventually need these high-speed interfaces, mostly HBM, to some extent, GDDR6. So these growth of AI into the data center, the data center market growth itself are driving growth for IP cores.
You know, IP core business is growing in double-digit growth, but the AI through HBM GDDR6 are the main drivers for that.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
So -- but would it be possible that this were early in adoption and perhaps if it materializes, it may provide upside to your expectation for this year and beyond? Or is it already dialed into what you have communicated for opportunities?
Luc Seraphin -- Chief Executive Officer
Maybe it is dialed in what we have communicated for our opportunities. The Rambus strategy has always been to focus on data centers and high-speed interfaces. So what we've done over the last few years is we focus our portfolio on the IP that serves those markets and HBM, GDDR6 controller, and PHY as well as a security IP focus on to benefiting from that market growth. So this is dialed in our expectations.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
Got it. Thank you. And just a quick follow-up. Your pro forma opex over the past fourth quarter has remained below $50 million.
Is this something that we should be thinking of over the next four to eight quarters like at most $50 million of opex?
Rahul Mathur -- Chief Financial Officer
Hi, Mehdi, it's Rahul. Thanks very much for the question, and we're delighted to have you on the call today. In terms of an opex perspective, look, I think we've done a fantastic job of improving our operational efficiency and in particularly taking cost out of SG&A. What you've seen is that we've taken probably about $20 million of cost out compared to where we were a couple of years ago.
My expectation is that from an overall opex perspective, our SG&A through the course of this year should stay roughly flat on a quarterly basis. There's always some ins and outs on a quarterly basis related to tax or hiring or other things as well. What I'd expect, though, is that if we had some increases in spend, it would be on the R&D side. We are investing in these very exciting product programs that Luc was talking about earlier, both on the chip side as well as on the silicon IP side.
So you might see a little bit of increase on the R&D side from a quarter-to-quarter perspective. But I think that, you know, 50 million a quarter, we should be under that through the course of this year. But I'd like to see us continue to invest in R&D toward the back half of this year and then out in the future to fuel these products -- plans that are growing very nicely. Maybe to the question you're asking earlier, you know, we look at our silicon IP business on total, as Luc mentioned, growing kind of in the double-digit range on an annual basis.
And that's embedded, I think, in the growth estimates that you see for analysts and consensus estimates. And I think I mentioned that in our prepared remarks.
Mehdi Hosseini -- Susquehanna International G
Seraphin -- Chief Executive Officer
Thanks, Sidney.
Operator
Your next question comes from the line of Mehdi Hosseini with SIG. Your line is open. You may ask your question.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
Yes, thanks for taking my question. Just want to follow up to Sidney's. And want to dig into silicon IP opportunities, especially with AI and machine learning. And this is something that, in my opinion, we're still in the early phase.
But I want to see how much of those incremental opportunities are part of your expectation? Or would this actually provide any upside to your overall opportunities for this year and beyond? And I have a follow-up.
Luc Seraphin -- Chief Executive Officer
Hi, Mehdi. The AI and ML opportunities do add potential revenue for our IP cores, especially HBM where we do show a very high-bandwidth capability, you know? AI is going to be consuming a large portion of the data center growth going forward. So anyone building a chip for AI that goes into data center will eventually need these high-speed interfaces, mostly HBM, to some extent, GDDR6. So these growth of AI into the data center, the data center market growth itself are driving growth for IP cores.
You know, IP core business is growing in double-digit growth, but the AI through HBM GDDR6 are the main drivers for that.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
So -- but would it be possible that this were early in adoption and perhaps if it materializes, it may provide upside to your expectation for this year and beyond? Or is it already dialed into what you have communicated for opportunities?
Luc Seraphin -- Chief Executive Officer
Maybe it is dialed in what we have communicated for our opportunities. The Rambus strategy has always been to focus on data centers and high-speed interfaces. So what we've done over the last few years is we focus our portfolio on the IP that serves those markets and HBM, GDDR6 controller, and PHY as well as a security IP focus on to benefiting from that market growth. So this is dialed in our expectations.
Mehdi Hosseini -- Susquehanna International Group -- Analyst
Got it. Thank you. And just a quick follow-up. Your pro forma opex over the past fourth quarter has remained below $50 million.
 Is this something that we should be thinking of over the next four to eight quarters like at most $50 million of opex?
Rahul Mathur -- Chief Financial Officer
Hi, Mehdi, it's Rahul. Thanks very much for the question, and we're delighted to have you on the call today. In terms of an opex perspective, look, I think we've done a fantastic job of improving our operational efficiency and in particularly taking cost out of SG&A. What you've seen is that we've taken probably about $20 million of cost out compared to where we were a couple of years ago.
My expectation is that from an overall opex perspective, our SG&A through the course of this year should stay roughly flat on a quarterly basis. There's always some ins and outs on a quarterly basis related to tax or hiring or other things as well. What I'd expect, though, is that if we had some increases in spend, it would be on the R&D side. We are investing in these very exciting product programs that Luc was talking about earlier, both on the chip side as well as on the silicon IP side.
So you might see a little bit of increase on the R&D side from a quarter-to-quarter perspective. But I think that, you know, 50 million a quarter, we should be under that through the course of this year. But I'd like to see us continue to invest in R&D toward the back half of this year and then out in the future to fuel these products -- plans that are growing very nicely. Maybe to the question you're asking earlier, you know, we look at our silicon IP business on total, as Luc mentioned, growing kind of in the double-digit range on an annual basis.
And that's embedded, I think, in the growth estimates that you see for analysts and consensus estimates. And I think I mentioned that in our prepared remarks.
Mehdi Hosseini -- Susquehanna International G