Page 2 : High-Bandwidth Cache, HBM2 Memory, Cache Controller, Why Is It Called A Cache?
AMD Vega will use HBM2 memory, as well as a new High-Bandwidth Cache Controller (HBCC). Together, they are known as the High Bandwidth Cache.
AMD showcased the performance of the High-Bandwidth Cache using a real-time render of Joe Macri’s living room on Radeon ProRender with 700+ GB of data. Although no frame rate was visible, the real-time render appeared to be very smooth.
The HBM2 Memory
HBM2 offers twice the transfer rate per pin (up to 2 GT/s), over its the first-generation HBM memory. This allows it to achieve up to 256 GB/s memory bandwidth per package.
In both HBM and HBM2, up to 8 memory dies can be stacked in a package. But moving to HBM2 allows for twice the memory density – up to 8 GB per package is now possible.
The High-Bandwidth Cache Controller
The second component of the High Bandwidth Cache is the new High-Bandwidth Cache Controller (HBCC). It creates a homogenous memory system for the AMD Vega GPU, with up to 512 TB of addressable memory.
It also allows for the adaptive, fine-grained movement of data between the AMD Vega GPU and the system memory, the NVRAM and the network storage (as part of Infinity Fabric).
Why Is It Called A Cache?
AMD calls the combination of the HBM2 memory and the High-Bandwidth Cache Controller the “High-Bandwidth Cache“. Techies may wonder why AMD chose to call it “cache”, instead of “memory”. After all, HBM2 memory is a type of fast graphics memory.[adrotate group=”2″]
The answer lies in the AMD Vega’s heterogenous memory system. All memory in the system, whether it’s the HBM2 memory or shared memory from the computer’s SDRAM, is seen as a contiguous memory space. A big block of memory, irrespective of how fast they are.
That may be great for memory addressing, but may cause frequently-used data to be placed in slower memory. To avoid such an occurrence, the High-Bandwidth Cache Controller uses the HBM2 memory like a fast cache. This allows it to keep the most frequently-used data in the fastest memory available – the HBM2 memory.
Hence, the HBM2 memory functions like a cache in AMD Vega, and that is why AMD called the combination the High-Bandwidth Cache.