In a surprise announcement late last week, some PS4 Pro owners running the beta version of the console’s firmware pointed others to a new feature that went undocumented by Sony, called “Boost Mode”. This is a new feature inside the console’s OS that disables the restrictions placed on old PS4 games that are not patched to support faster rendering modes on the PS4 Pro. With it enabled on selected games set by the user, these games may be able to run faster if they have an unlocked framerate, or if their framerate is generally lower than the 30fps minimum that Sony tells developers to aim for.
If you’re late to the party about the PS4 Pro patch, you can catch up quickly by reading one of my old columns, “Some misconceptions about the PS4 Pro need to be cleared up.” In it, I mention patent application US20160246323A1 that PS4 designer Mark Cerny made on behalf of Sony, detailing how the PS4 Pro is able to emulate the hardware inside a standard PS4 with a high degree of accuracy, despite the PS4 Pro being faster and having a much more powerful GPU. The following passage is copied verbatim from the patent’s explanation of Sony’s emulation technique:
“To give an example, the GPU of the prior version of the system might run at a GPU clock of 500 MHz, and the current system might run at a GPU clock  of 750 MHz. The system would run with  set to 750 MHz when an application is loaded that is designed only for the current system. In this example, the cycle counter [CC] would correspond to the 750 MHz frequency (i.e., it is a true cycle counter). When a legacy application (i.e., an application designed for the prior version of the system) is loaded, the system  may run at a frequency slightly higher than the operating frequency of the prior system (e.g., with  set to 505 MHz). In this backward compatible mode, the GPU spoof clock  would be configured to run at 500 MHz, and the cycle counter CC would be derived from the spoof clock, thus providing the expected value to the legacy application.”
The technique here is a type of emulation, but it is different to the emulation that Sony uses to run PS1 games on the PS4, or that Microsoft uses on the Xbox One to provide backwards compatibility for Xbox 360 games. Both of those techniques rely on a software translation layer that interprets commands that the chips in the old consoles would have understood natively, while the PS4 and Xbox One have chip architectures that are vastly different.
Boost mode builds on patent US20160246323A1 by offering higher clock speeds to the game than it originally had, boosting performance in games that need all the help they can get. In the system menu on systems running system software 4.50, this is description for the feature:
“Experience improved gameplay,including higher framerates, for some games that were released before the introduction of PS4 Pro (CUH-7000 series). Turn this off if you experience unexpected behaviour during gameplay.”
Digital Foundry was the first to test out these changes that Boost Mode offered, and they ran though a gamut of games that traditionally ran very poorly, often with minimum framerates dropping to 22fps in some places. Everything from Assetto Corsa, Project Cars, and Assassin’s Creed: Unity, to Knack saw a boost in performance. Older launch games which didn’t run very well saw an immediate boost, quite similar to the way old Xbox 360 titles run slightly better on an Xbox One thanks to higher throughput on the GPU. Both their initial and follow-up testing videos are embedded below:
So why is that patent relevant? Well, the PS4 Pro still isn’t offering all of its power to these older, unpatched games. The way Sony went about their emulation is to offer slightly higher clock speeds than the original hardware in order to keep the spoofed system clock running on time – 505MHz vs 500MHz, for example, to work around any hiccups or stalls in the rendering pipeline. Boost mode offers increases to both the GPU and CPU clock speed, but there are several games in Digital Foundry’s test run that see as little as a 14% framerate boost (mostly GPU-dependent titles), jumping up as much as 35% in the case of Project Cars, which is both CPU and GPU intensive. Not every game running on the PS4 Pro benefits from Boost mode in the same way, despite the fact that it just mimics a faster PS4.
Not every game is going to run with Boost mode enabled either, because some games may be unplayable due to issues that can’t be resolved without disabling it. In the patent for the PS4 compatibility mode, Mark Cerny explains that the system uses a cycle counter to emulate the lower clock speeds of the PS4, and running those games at the full 2.1GHz clockspeed of the CPU, for example, might be problematic for things like Havok CPU-based physics, which relies on particular commands or threads being completed in a specific number of cycles. Only games that were designed to allow an unlocked framerate in the beginning, or that have no requirements for particular workloads being completed in a specific amount of time, would be able to compensate for the extra speed.
The fact that the toggle for Boost mode is optional and hidden in the system settings menu, and that it requires users to enable it, also tells me that Sony would rather avoid controversy by not enabling it for everyone. This way, it requires anyone who knows what Boost mode is to accept the fact that it won’t work across the board. This ties in with a statement that Sony made to Digital Foundry after they started testing the benefits of Boost mode:
“Boost Mode has been designed to provide better performance for those legacy titles that have not been patched to take advantage of the PS4 Pro’s faster CPU and its faster and double-sized GPU,” Sony says. “This can provide a noticeable frame-rate boost to some games with variable frame-rate, and can provide frame-rate stability for games that are programmed to run at 30Hz or 60Hz.
“Depending on the game, the increased CPU speed may also result in shorter load times. Boost Mode is not guaranteed to work with all titles, however, turning the setting off will allow the game to be played in a mode that replicates the standard PS4. As an aside, the older unpatched titles that run in Boost Mode are unaware that they are running on a PS4 Pro and consequently don’t take full advantage of the PS4 Pro capabilities; power consumption for these games will therefore be a bit lower compared to playing a newer title.”
If you were on the fence before about buying a PS4 Pro, this is a pretty good reason to look at getting one sometime this year.