Rocket Lake (RKL) is Intel’s new micro-architecture that will be a direct successor to the Comet Lake-S series of desktop CPUs and high-performance mobile devices. These were expected to hit the market by the end of this year, but the roadmap from Intel paints a slightly different picture.
Intel has been using the same iteration of the 14nm FinFET process node with the Skylake Architecture for many years. Comet Lake-S was also fabbed on this aging process node, which has held Intel back in terms of IPC uplift and efficiency gains over AMD’s Ryzen lineup. The Rocket Lake-S desktop platform is hopefully going to be the last CPU architecture to be based on an advanced 14nm process node. Intel’s Rocket Lake will use a 14++ nm ‘back-port’ of the Willow Cove core architecture. Intel plans to focus more on the single-threaded performance with this new CPU lineup.
If recent rumors are to be believed, Rocket Lake will offer fewer cores than today’s Comet Lake-S series of processors, maxing out at eight cores and twelve threads. Strangely enough, Intel’s Rocket Lake-S lineup was not mentioned during the Q2 earnings call, and it was also not present in Intel’s press release or Q&A session. Though, the company did confirm that the successor ‘Alder Lake-S’ lineup is going to launch in the second half of 2021, meaning Rocket Lake-S might arrive a bit sooner than previously expected. The series could launch in late 2020 or early 2021.
Rocket Lake Desktop CPUs will also be the first to support the PCIe Gen 4.0 protocol, and this support has now been confirmed in a leaked entry as spotted by TUM_APISAK over at the SiSoftware database. Till now support for the PCIe gen 4.0 interface has been rather limited in Intel’s lineup/stack of processors, with only 10th Gen Core ‘Ice Lake-U’ and ‘Ice Lake-Y’ mobile processors supporting it so far. The upcoming 11th Gen Tiger Lake mobile processors will also support it. But the new SANDRA database screenshot shows a Rocket Lake-S powered machine running a PCI-Express 4.0 NVMe SSD.
This new Rocket Lake-S Desktop engineering sample was tested with a PCIe SSD having 1 TB of capacity and was running in PCIe 4×4 mode. The device provides a bandwidth of up to 1.2 GB/s and I/O speeds of 45,000 IOPS. This confirms that Rocket Lake-S will be the first platform on Intel’s side to offer PCIe Gen 4.0 support. This sample is presumed to have a 32 EU Gen 12 Xe GPU, making up for a total of 256 cores. The I/O section of Rocket Lake-S platform also shows some progression. The CPU socket not only puts out its usual PEG slot (16 lanes for PCI-Express), but also a CPU-attached M.2 NVMe slot with 4 PCI-Express gen 4.0 lanes, much like the AMD X570 or B550 chipset. Intel has beefed-up the chipset bus with 8 lanes. Even though the bus is still DMI 3.0 (PCI-Express gen 3.0 physical layer), 8 lanes could mean a doubling in bandwidth compared to the 400-series and older chipset. The 500-series PCH will still be PCI-Express gen 3.0 based though, unlike the AMD X570 which uses a PCI-Express 4.0 x4 pipe to the CPU. According to _rogame, Rocket Lake-S is using the ‘Cypress Cove’ core architecture.
The Rocket Lake CPUs will also support the LGA 1200 socket and the high-end Z490 motherboard chipset. The Z490 motherboard has readiness for PCIe Gen 4.0, but the current Comet Lake-S Desktop CPU lineup lacks support for this Gen 4.0 protocol. But since hardware-level support for PCIe 4.0 is already built-in these Z490 boards, only Rocket Lake CPUs are going to offer compatibility of the PCIe Gen 4.0 standard. PCIe- 4.0 has been an AMD-only feature within the consumer market till now, but things might change with the launch of Rocket lake-S CPUs. Most of the motherboard vendors like MSI, ASRock, and Gigabyte have already given some form of PCIe Gen 4.0 support on their Z490 boards, which means hardware-level features are also supported. So end users/gamers will not have any problem plugging in any PCIe Gen 4.0 device, and get access to higher transfer speeds that this new protocol offers, when the Rocket Lake-S CPUs arrive on shelves. This rumor was already confirmed before by motherboard makers, who announced PCIe 4.0 hardware readiness for the next-gen Intel core CPU series.
Recently, MSI also confirmed Rocket Lake-S support on their entry-level H410 chipset motherboard series. Few months ago, WccfTech confirmed that the Rocket Lake-S desktop CPUs are only going to be compatible with the Z490 chipset and LGA 1200 socket motherboards, since Motherboard vendors heavily advertised that these boards are PCIe-4.0 ready. But now it appears that the mainstream and low-end 400 series boards are also going to offer support for Rocket Lake-S. GIGABYTE has already confirmed that their Z490 AORUS lineup of motherboards support limited PCI-E 4.0 capabilities on Comet Lake-S CPU lineup, which makes sense given these processors do not support all the features of the PCI-e 4.0 interface. But this places Intel’s Z490 platform longevity in a difficult position, since INTEL won’t be supporting the LGA 1200 socket for long. LGA 1200 based motherboards are probably not going to stay for a long time, as Z490 is only expected to support Comet Lake-S and Rocket Lake-S CPU series, while Alder Lake-S is already rumored to feature the new LGA1700 CPU socket.
According to previous rumors Rocket Lake will deliver desktop users up to eight cores and sixteen threads on the high-end, which means two cores and four threads less than the current Comet Lake processor lineup. But the reduction in core count could also mean that Intel plans to rely on increased single-threaded performance, thus boosting overall system performance through single-threaded gains. Single-threaded performance will help Intel to compete more in the CPU market segment, even if AMD can deliver higher core count SKUs. Not all applications/tasks are highly multi-threaded in nature, which makes the single-threaded performance all the more important.
When it comes to the Rocket Lake-S CPU lineup, I have another piece of info to share with you. Few months ago, one VLSI engineer who also goes by the name Retired Engineer on his personal Twitter account, @chiakokhua, tweeted one of his old findings from November 2019 last year. According to him the upcoming Rocket Lake-S processors are going to feature ‘multi-chip modules/MCM’ of core and uncore GPU dies built on different silicon fabrication nodes. This is speculation from his side, but he has a strong record of accurate prediction in the past, when he spoke about the 3rd gen Ryzen Matisse AM4 processors being multi-chip modules as well.
Apparently, it might be possible that Intel is also designing these socket LGA1200-based Rocket Lake processors to feature multi-chip modules, similar to Matisse in some ways. According to the block diagram posted by @chiakokhua, it appears that Rocket Lake-S is a multi-chip module consisting of a 14nm die that holds the ‘CPU cores’; and a 10 nm die that holds the ‘uncore’ components. But in the case of Rocket Lake the uncore die is more advanced that the CPU die.
The CPU die is fabbed on a 14 nm node on Rocket Lake-S, which contains the Willow Cove CPU cores in this die, and a system agent, which are connected together by a Ring-bus interconnect. And the system agent connects to the 10nm uncore GPU die via EMIB. The 10 nm GPU uncore die on the other hand features the Gen12 XE iGPU with up to 96 EUs, a dual-channel DDR4 memory controller, a PCI-Express 4.0 controller, as well as display and media engines. Rocket Lake-S MCM provides a total of 24 PCI-Express lanes, out of which 16 are assigned as PEG (PCI-Express Graphics), and 8 lanes are assigned as chipset bus. Previous gen Comet Lake-S CPU lineup only provided us with 20 lanes.
This is not the first time Intel is taking the MCM approach. Clarkdale, first-gen desktop processor supporting the LGA1156 package was an MCM having a 32 nm CPU die, and a 45 nm uncore graphics and integrated memory controller die. It remains to be seen whether Intel really chooses the MCM approach with the Rocket Lake- S lineup of desktop processors.