Streaming SSD, How It Works and What Advantages it Brings in Video Games.

Solid disks or better known as its acronym in English: SSD , are one of the most important pieces of hardware for games in the coming years and not only to accelerate loading times, but also for continuous access to data from the disk by the game itself. But what do these improvements translate into? How does the SSD benefit data streaming ?

Game data streaming from disk

There are two ways to design a game in terms of level architecture

• The first is to do it by levels in which we divide the game into delimited areas not communicated with each other, the player has an objective that when it is fulfilled the next area opens.
• The second is an open world completely interconnected with each other, there are no divisions and we can have a continuous transition throughout the world.

Well, the second type has not occurred until now due to the fact that despite the fact that at an aesthetic level it may seem to us that there is continuity, there are always traps to hide that the levels are loading. These can be a cinematic, a very large hallway, an elevator, and even an action scene on a very small screen while the rest of the stage is loaded in the back room.

With the SSD, not all the data in memory is necessary for streaming

But if the transfer speed is high enough then we can avoid those pitfalls completely and make the second type of scenarios completely possible and this is where the use of solid drives as a replacement for hard drives comes in.

The trick is that as the player approaches a non-charged area to use the internal telemetry of the game so that the scenario in which we are going charges beyond the horizon. If this is done well then the virtual world will move its borders according to the position of the player in it and if it is done adequately enough, the loading times will be able to be dispensed with without having to dump all the data from the level to RAM.

But to understand what the advantage is, we must first understand what are the handicaps of the traditional hard disk and the advantages of using a solid disk.

The hard disk and its disadvantages for data streaming

A Hard Drive is to be a rotating circular storage medium, which is organized in a series of concentric circles called “tracks”, where each track has a series of “sectors” whose standard size is usually 512 bytes. Depending on the file system used by the operating system, the tracks are organized into groups of various idems called clusters, which correspond to the minimum size that a file has on that system of the file system used by the operating system, the size of a file can never be smaller than that of a cluster.

The problem with hard drives is that depending on the track in which the data is located, the speed you want to access, then the access speed varies. For the outermost tracks, the data access speed is faster, and it becomes slower for the tracks that are further inside due to the fact that the head has to change tracks, thus the data access latency of the hard disk will always depend on where they are.

This is a huge problem for streaming, since the data we need in the short term in the game can be found on one of the internal tracks of the disc, which can lead to the stage not being built fast enough and force stages. of Transition.

But it is not the only existing problem, the other problem is that we need to use an address table, a file located in RAM and / or on the hard disk itself that has to be continuously consulted by the CPU to know where the data is. . This ties the hard drive to a file system related to the operating system and prevents any processor without an MMU as complex as a CPU from accessing the hard drive.

All these handicaps mean that hard drives are not the best storage medium from which to stream data.

Access to the SSD and its advantages for data streaming

SSD disks use non-volatile RAM (NVRAM) or better known as flash memory, the best known and most used being the NAND type.

All this means that the MMU can access the SSD as if it were RAM memory and treat it as an extension of it for addressing, which makes it possible to completely dispense with a file system. This is also what allows a GPU that has a much simpler unit than a GPU to have access to the SSD since it does not have to run an operating system, the latter allows expanding the storage capacity of the graphics.

For example, one of the things that increases efficiency is with virtual texturing, which is that we only have in memory the textures that are necessary for the frame and not the entire memory map. With the hard disk we need to bring entire memory pages but with an SSD we can choose what data and in what volume we want to be copied from the solid disk itself to RAM.

The SSD memory is NVRAM but the system does not access as if it were RAM memory

Well the answer is no, actually at the physical level there is no direct addressing with the SSD but when we talk about unified addressing we mean how the MMU sees the system memory from the same virtual addressing.

When a set of memory pages of the virtual address is not available in RAM, what the MMU does is send a request to the IOMMU and this to the SSD controller. What the SSD controller is going to do is translate the memory address that has arrived into a physical address of the SSD where the data that we want to obtain or modify is located.

The problem is that this data search process is very tedious and slow and what is done is to take advantage of the enormous bandwidth of the PCIe interface to copy large volumes of data from the SSD to a RAM space used as a kind disk cache. It is precisely the speed of the PCIe interface that eliminates these transitions in game design.

It is possible that in a few years, at least in some games, the term level will disappear completely and it will all be thanks to what we have just explained to you