Although there has been plenty of hype surrounding Ryzen Threadripper, AMD kept many of the technical details surrounding the CPUs secret until the launch was imminent. One such titbit of information was discovered by professional overclocker deb8auer: Threadripper CPUs are in fact repurposed EPYC server chips, contained four Ryzen CPU (i.e. Zepplin) dies of which two had been fused off. That’s quite a revelation, and in of itself has intriguing implications for the future, but for now we’ll focus on the practicalities.
Each Ryzen Threadripper CPU has only two of four Zepplin dies active, for a maximum of up to 16 active CPU cores (the actual number of active cores depends on SKU). These dies are always a diagonal pair, to some extent equalising the heat distribution from the CPU under its heatspreader whilst under load.
With two cores fused off the package supports quad-channel DDR4 memory, a first for an AMD desktop product. Motherboards using the X399 chipset will typically be kitted out with 8 DIMM slots for DDR4 memory, and can support up to 1TB of LR-DIMMs (128GB per slot). Most customer configurations will likely top out at 64 (4 x 16GB or 8 x 8GB) or 128GB (8 x 16GB) DDR4 memory, depending on application.
CPU Cache levels for Threadripper CPUs is derived from the Ryzen dies present in its configuration. Each core features 512KB of dedicated L2 cache, not shared between the cores. Also present on a 4-core CCX is a total pool of up to 8MB L3 cache, accessible by all the cores on the die (not just those enabled in its CCX). In total therefore the Threadripper 1950X is equipped with 8MB L2 cache and 32MB L3 cache – frankly a gargantuan amount.
Level 3 cache in the Zen architecture is what’s known as a victim cache. Usually at least as large as the higher level cache, a victim cache stores blocks of data as they are evicted from the higher level. Should a miss occur on L2 cache for instance, L3 cache will then be looked up for the block, reducing the number of cycles needed to otherwise find the data in system memory.
One critical capability of Threadripper is the across-the-board availability of 64 PCI-Express 3.0 lanes, no matter the number of cores enabled on the chip. This compares extremely favourably with Intel’s maximum of 44 on the Core i9 7900X, and more general access to 28 on 8-core and 6-core parts on their HEDT platform. We should of course note that AMD’s figure includes lanes reserved by the chipset (a total of 4), but nonetheless that’s quite a competitive advantage.
The value and versitalitity of more PCI-Express lanes is not something we’ll be able to capture in this launch review. Previous generations often leveraged the additional bandwidth by making use of multiple GPU SLI/CrossFire configurations, but support for n-way graphics on discrete GPUs is in the process of being depreciated by AMD and NVIDIA. Currently only 2-way SLI is officially approved by NVIDIA for consumers, whilst recently AMD place no emphasis on CrossFire for Vega (although the GPU is technically capable of this feature).
A more recent development has been use of NVMe storage. High speed SSDs utilising M.2 or U.2 with PCI-Express signalling are easily capable of surpassing the limitations of SATA III, pushing read rates that exceed 2GB/s. It’s scenarios which utilise this vast quantities of this storage (in a RAID array or similar) that can really take advantage of additional PCI-Express lanes.
Users who combine high bandwidth storage and graphics in one system - for use with gaming, streaming and video editing (potentially in real time) for example – could thrive on the Threadripper platform. However if all you’re doing is a spot of gaming and streaming, Rysen might be the AMD platform for you.
It should be noted that Threadripper X399 isn’t currently capable of booting from NVMe Raid Arrays.
A new CPU architecture often means that the CPU socket needs to be updated, and such is the case with Threadripper. AMD’s gargantuan new CPU utilises a variant of their SR4 EYPC server socket they’re calling TR4, sporting 4096 contact points, but SR4 and TR4 solutions are currently incompatible. That’s a major increase over the 1331 contacts of Socket AM4, and accounts for the higher level of signalling complexity required by the new CPU.
TR4 is a Land Grid Array (LGA) type socket, meaning that pins are located on the motherboard side with contact pads printed on the underside of the CPU. As a result the CPU package is far less fragile, reducing the chances you’ll incur damage when handling it, but the installation process can be a little bit more complex.
Due to the size of the Threadripper CPU package TR4 has a massive footprint compared to existing desktop sockets. That has posed a unique challenge to motherboard manufacturers working within the confines of existing motherboard standards, and cooling solutions will also require a update to the new mounting system. We don’t yet know whether mATX and other small form factor motherboard designs will be possible using the TR4 socket, but currently EATX appears to be the standard of choice. Ensure that your chassis can accommodate it before you buy.