The PlayStation 5's built-in boost mode is much, much more powerful than the PlayStation 4 Pro's. Sony says the boost is so dramatic that some older PS4 games simply can't handle it.

The PS5's backward compatibility is pretty lackluster in terms of supported games. Unlike the Xbox Series X, which can play OG Xbox, Xbox 360, and all Xbox One games at launch, the PlayStation 5 will only support 100 of the most popular PS4 games. But why? The PS5's native boost mode is the culprit. Here's how it works.
Like the Xbox Series X, the PlayStation 5 will natively boost any PS4 game you put into it. For example, Xbox Series X will auto-upgrade 2015's Gears of War 4 to native 4K resolution. Sony's PS5 will also boost PS4 games, but Sony hasn't detailed specifics. We could see all sorts of perf boosts like 120FPS, ray tracing, and more--imagine playing Bloodborne at 1080p 120FPs.
Sony did outline how PS5 backward compatibility works, though.
The PS5's new 10.3 TFLOP Navi GPU and 8-core Zen 2 CPU will automatically scale performance to emulate PS4 and PS4 Pro hardware via new Legacy Modes. But even in these legacy-optimized modes the games will be boosted quite a bit--so much that some games simply can't handle it.
- Native Mode - Fully unlocks the Navi GPU at 2.23GHz for next-gen games
- PS4 Pro Legacy Mode - Downscales the GPU to 911MHz, 218GB/sec bandwidth, and 64 ROPs to emulate the PS4 Pro
- PS4 Legacy Mode - Drops the GPU to 800MHz with 176GB/sec bandwidth and 32 ROPs to emulate the base PS4

So basically developers have to work alongside Sony to get older games running on the PS5. That's why there's so few titles supported at launch, and why Sony asserts new games have to be added on a title-to-title basis.
"Running PS4 and PS4 Pro titles at boosted frequencies has also added complexity. The boost is truly massive this time around and some game code just can't handle it. Testing has to be done on a title-by-title basis," PlayStation 5 architect Mark Cerny said in a recent presentation.
With its new 2.23GHz Navi GPU, 3.5GHz Zen 2 CPU, ultra-fast customized 825GB SSD, and 16GB of unified GDDR6 RAM, the next-gen PS5 is simply so advanced that engineers have to tweak the game's code--or tweak how the SoC responds to older game code--to get certain games running on the platform.
Expect first-party PS4 games to look, feel and play absolutely amazingly on the next-gen PlayStation 5.
"Results are excellent though. We recently took a look at the top 100 PlayStation 4 titles as ranked by play time and we're expecting almost all of them to be playable at launch on PlayStation 5."
"Achieving this unification of functionality took years of efforts by AMD as any roadmap creates a potential divergence in logic. Backwards compatibility was handled masterfully by AMD. They treated it as a key need through the design process.
The PlayStation 5's SSD will be a big part of this new boost mode functionality, and we recently did a deep-dive on the system's remarkable new custom storage tech. Find that here.
The console will release in Holiday 2020, and it may cost $499.
Check below for more info on everything we know about the PlayStation 5 so far:

PlayStation 5 specs and details:
- Custom SoC with second-gen Navi GPU, Zen 2 CPU
- 8-Core, 16-thread Zen 2 CPU at 3.5GHz
- Navi 2X GPU with 36 CUs on RDNA 2 at 2.23GHz
- Ultra-fast 825GB SSD with up to 9GB/sec speeds
- Support for 4K 120 Hz TVs
- Ray-tracing enabled
- 8K output support (for gaming)
- Plays PS4 games, BC is on a title-to-title basis
- Separate games that ship on BD-XL Blu-ray discs
- New controller with extensive haptic and tactile feedback
PlayStation 5 Coverage:
- PS5 won't play PS1, PS2 or PS3 discs, 100 PS4 games supported at launch
- Understanding the PS5's SSD: A deep dive into next-gen storage tech
- PlayStation 5 won't use memory cards, supports third-party SSDs
- PlayStation 5 specs: 10TFLOPs Navi RDNA 2 2.23GHz GPU, 3.5GH Zen 2 CPU
- PlayStation 5 SSD speeds hit 9GB/sec with custom 12-channel controller
- PlayStation 5, Xbox Series X ray tracing is easily scalable for devs
- Report: PlayStation 5 Pro and base PlayStation 5 coming in 2020
- 60FPS on next-gen PlayStation 5, Xbox Series X 'is much easier'
- PlayStation 5 specs confirmed by Sony: 10TFLOPs Navi RDNA 2 2.23GHz GPU, 3.5GH Zen 2 CPU
- PlayStation 5 could use Samsung's 980 QVO SSDs
- PlayStation 5 is beating Xbox Series X in dev kit form right now
- Hardly any devs are making next-gen PS5, Xbox Series X games
- Sony working on new horror IP for PlayStation 5
- PlayStation 5 devkit UI possibly leaked
- Leaked PlayStation 5 concepts show weird X-shaped case
- Sony's first-party PS4 exclusives are coming to PC
- PlayStation 5's new DualShock 5 may be usable on PS4
- Sony skips E3 2020, has two major events planned for February
- Next-gen console exclusives will be few and far between through 2021
- PlayStation 5's biggest features have yet to be announced, Sony says
- PS4 has sold over 1 billion games and 106 million consoles
- PlayStation 5 backward compatibility should support every PS4 game
- Sony reveals the PlayStation 5...logo
- New trapezoidal PS5 render is an expensive accident waiting to happen
- A $399 PlayStation 5 will conquer next-gen
- PlayStation 5 to outsell Xbox Series X in 2020, analyst predicts
- PS5 may only enhance PS4 games, legacy PS1, PS2 and PS3 games unlikely
- PlayStation 5 prototype dev kit console gets V-shaped clean
- Sony: The future is coming at CES 2020
- PlayStation 5 GPU: 9.2 TFLOPs with 36 custom Navi compute units
- PlayStation 5 GPU emulates PS4, PS4 Pro with special modes
- PS5, Xbox Series X SSD may use software-defined flash to boost speeds
- PS5's SSD is 'exceptionally powerful,' may beat Xbox Series X speeds
- DualShock 5 renders show new trigger design, USB-C, ergonomic shell
- PlayStation 5 to support 8K gaming, Sony confirms
- New PlayStation 5 renders show off radical different design, again
- Leaked PlayStation 5 ad prices console at $1,000, is totally fake
- Sony seeks a new Head of Strategy for Worldwide Studios
- Leaked PlayStation 5 devkit photos show new DualShock controller
- PS5, Xbox Scarlett SSD may use Optane-like ReRAM to supercharge speeds
- NVIDIA G-Sync monitors to improve PlayStation 5 and Xbox Scarlett
- PlayStation 5: Everything We Know So Far
- PlayStation 5 confirmed to have 8C/16T Zen 2 CPU from AMD
- PS5, Project Scarlett may use Samsung's 6th gen V-NAND NVMe SSDs
- PS5 backward compatibility confirmed, will play PS4 games
- Sony's next-gen PlayStation 5 has 4K 120Hz output support
- PS5, Project Scarlett to hit over 10TFLOPs of power, sources say
- PS4 will be supported into 2022, to live alongside PS5
- Sony: ultra-high-speed SSD is 'the key' to next-gen PS5
- PS5 dev kit rumor: 'ultra-fast RAM', Navi GPU with 13 TFLOPs
- PlayStation 5 rumored to ship with 2TB of super-fast SSD for $499
- Insider: PlayStation 5 dev kit faster than Xbox Scarlett right now
- PS5 cartridges aren't real, patents are for Sony kids toys
- PS5's SSD may benefit PS4 games the most
- PS5 powered by Navi in 2020, AMD making Navi with Sony input
- Cloud-powered PlayStation controller may let you play free game demos
- Gran Turismo 7 is a PlayStation 5 launch title: launches Nov 20, 2020
- PS5 confirmed to support 8K video, ray tracing, all on Navi
- PlayStation 5 rumored to cost $499, launches November 20, 2020
- PlayStation game demos are coming back with Sony's ambitious new plan
- PS5 controller: Built-in mic, USB-C, no lightbar, ergonomic design
- PlayStation 5 concept video shows totally new design
- Sony solves PS5's biggest issue
- Sony: PS5 development going according to plan
- New Viking Assassin's Creed may be next-gen console launch game
- AMD working on 'secret sauce' for next-gen Xbox/PlayStation
- The first real photo of a PlayStation 5 dev kit appears
- Next-gen PS5/Xbox Scarlett open-world game: 'best real-time graphics'
- Sony restructures workforce to prepare for PS5
- PlayStation VR 2: built-in cameras, wireless, ready for PS5
- PS5 games will ship on 100GB Blu-ray BDXL discs
- PS5 and Xbox Scarlett will both handle ray tracing differently
- PlayStation 5 could feature AI-powered 'PlayStation Assist'
- Sony won't abandon singleplayer story-driven games on PS5
- PS5 rumor: GPU is nearly as powerful as RTX 2080, GPU clocked at 2GHz
- PlayStation 5 rumored to be unveiled on February 12, 2020
- Sony to raise PS5 cost thanks to U.S. tariffs