✅ You will reduce the game size on your disk from 7566 MB to 1298 MB (5.83x reduction).
✅ This way you will get over 6 GB of totally free disk space for other games or programs.
✅ You will be able to play the game normally like nothing happened.
✅ You won't delete or convert any game data. The method is quick, simple, lossless and transparent in your operating system.
✅ You won't have to download or install any additional software. GUI for faster and easier usage is entirely optional.
✅ The massive data reduction means there is less data to read from disk, so the game can load faster from HDD or even SSD drives (especially slow eco drives used in laptops).
✅ The process is easily reversible. See "Reversal" section for instructions.

This guide is only for Windows 10 where -83% disk space reduction is possible. If you are using older Windows systems, please use this guide instead:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2120130739

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🟨 Important: If you used my previous guide for older Windows versions (link above), first thing you need to do before progressing further is to decompress the Hollow Knight folder. See the "Reversal" section of the guide above.

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This method is easier for beginners, since it uses a GUI. This simplifies the process and makes it more functional and optimized. See Method #2 if you don't want to download anything.

Go to CompactGUI GitHub[github.com]. Under the Assets section click CompactGUI.exe to download. Save this little program for example in:

Launch CompactGUI.exe. Click the Settings cog wheel.

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Check Skip Files that are Poorly Compressed and Add to Explorer Right-click Menu. Click Save. Close the window and close the program.

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Close Hollow Knight if it's running.
Then go to Steam Library ➡️ Hollow Knight ➡️ Manage ➡️ Properties...

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Local Files ➡️ Browse Local Files...

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Go one step up to common folder.

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Right-click on Hollow Knight folder and select the newly appeared option Compact Folder.
If Compact Folder doesn't appear, you can always choose the folder manually directly in the CompactGUI window.

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Select LZX Compression Algorithm. Then click Compress Folder.
See "Important information" section for more info about this.

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Files are being compressed. Wait till the process completes. Speed depends mostly on your CPU. After completion you will recieve a notification with how much space you just saved on your disk.

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You can now close the CompactGUI window and go back to playing Hollow Knight! Have fun 🙂

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This method is less optimized, but it doesn't require downloading any additional GUI. We will use the compact.exe system program. I still recommend using the CompactGUI, because it will save time and optimize loading times of the game by automatically ignoring files that are poorly compressible.

Go to your Hollow Knight folder (Step 3 in Method #1). Click File ➡️ Open Windows PowerShell as administrator.

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Type:
And press Enter. Make sure you are in the Hollow Knight folder in PowerShell before pressing Enter.

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Wait for the compression process to complete. Speed depends mostly on your CPU and can take a few minutes. After finishing you should see this text in the PowerShell window:

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Now you can close the PowerShell Window and play Hollow Knight. Have fun 🙂

⚠️ Please read important information section first before trying it on any other game than Hollow Knight.

You can use CompactGUI for other games and even programs. Feel free to experiment. These lists may be helpful:

Games and Programs list with disk space gains (Wiki #1)[github.com]
Games and Programs list with disk space gains (Wiki #2)[docs.google.com]

See also game Depots section of any game on Steam in SteamDB:
https://steamdb.info/depot/367521/
If the Download Size is much lower than the Size on disk, it is a good indicator that the game is very compressible.

CompactGUI will often also show you approximated space gains. When you see not a lot of % gain, it usually means it's not worth it to use compression at all. Those approximations can sometimes be wrong, so it is optimal to always verify the information in practice.

🟩 This method uses the new Windows 10 LZX Compression[theitbros.com] to reduce the game folder's size on the disk. It has higher compression ratio and is faster on multi-core CPUs than the old NTFS File Compression (LZNT1)[en.wikipedia.org].
🟩 This method will work on all games with uncompressed game data files on the disk.
🟩 Despite smaller size, the actual data on the disk is not changed. The compression is lossless.
🟩 Windows 10 LZX Compression (like all data compression types) uses some CPU time to decompress data on the fly. The faster the CPU, the faster the max decompression speed. This means that the slower the disk is, the lower the CPU usage (for the decompression of data) and the better the load times gains (compared to uncompressed data on the same disk and CPU).
🟩 The reading of the compressed files is transparent to the user and programs/games. Windows 10 does the decompression of each file automatically in memory, and the game/program doesn't know it.
🟩 Most games already store pre-compressed data on the disk to reduce size and speed up loading times from HDD drives. Hollow Knight on PC is one of the exceptions, that's why it has such high gains.
🟩 Data compressed with the new LZX or XPRESS algorithms cannot be read by anything other than Windows 10.

There are three ways to reverse the process. Any of them will work no matter which method you had chosen for compression.

Just make a copy of the compressed game folder in the same place (Ctrl + C then Ctrl + V). Then delete (or rename) the compressed folder, and rename the folder of the copy you made to the original name ("Hollow Knight"). Done!

🔵 Tip: You can store the same game folder compressed with different algorithms. Just rename it instead of deleting (like "Hollow Knight - LZX"). You can use this for quickly testing the speed and size of different algorithms on the same disk and then selecting the one you liked the most.

Right-click on Hollow Knight folder and select Compact Folder (the same like you did in Steps 3–4). Then click Analyse Folder. Wait for it to complete, then click Uncompress Folder.

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Open the PowerShell window in the Hollow Knight folder like you did before. Type:

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Press Enter and wait for the process to complete.

Please read the Important Information for using Windows Compression[github.com] by the author of CompactGUI. It should answer all the important questions that you have.

🟦 Only one compression algorithm can be used for the same file on the disk at the same time.
If you wish to test another algorithm, make a copy of the folder or uncompress the folder first (see "Reversal" section).

🟦 Using Windows File Compression on other games and data
Using compression for a game folder, which has already precompressed data on the disk, will put completely unnecessary additional load on the CPU (decompressing the same data two times at the same moment). This will of course hurt loading times and will not bring as much data size reduction (if any at all). Additionally, compressing sound, music and video files is also not optimal. Try to avoid compressing those file types if you have the chance.

CompactGUI will take care of this for you and will try to avoid compressing most poorly compressible file types automatically (highly recommended).

🟦 Is it safe to use compression on SSD for games and programs?
Yes. Most games are already storing compressed data to save space. The compressed data is safe for SSD when used mostly for reading data. Decompressing is done in memory. There is of course the one-time cost of some additional writing during the initial compression. So the less frequently you install and compress games, the better. If you used the older LZNT1 compression on a whole folder that is often modified and writes new data very frequently (like a temporary folder for a browser) then it would be much less safe for SSDs in the longer term and this is not recommended.

CompactGUI method is very safe and even tries to avoid unnecessary writing in the first place by ignoring poorly compressible file types. It will also not automatically recompress the files if they were modified (highly recommended for games/programs).

🟦 What compression algorithm to choose?
Choose LZX for Hollow Knight. If the game or program you compressed runs not as fast as you would like on your CPU + disk combination on LZX, then decompress the folder or make a copy, and compress it using XPRESS16K. If you are compressing data that needs to be read on previous Windows systems as well, you can use the old LZNT1 (see my previous guide). If the game or program runs worse after any type of compression, then there is no reason to compress it (except only for pure disk space gain).

🟨 Note: Author of CompactGUI recommends XPRESS8K or 16K instead of LZX. But in practice reading speed differences between all algorithms are so small that you shouldn't even notice them unless you would have a very slow CPU and very fast SSD, which is very unlikely. Therefore I choose the algorithm which gives the best compression, which is LZX. It takes much more time to compress on SSDs and slow CPUs, but gives more disk space. Don't believe me. Testing the differences on your own system and on your own games/programs is always recommended.

🟦 Disk/storage formatting requirements for Windows File Compression
To be able to use Windows File Compression the disk on which the game is stored has to be formatted using NTFS file system. It is used by Windows systems as default for non-removable drives so it shouldn't be a problem in most cases. Plug-and-Play storage like Pendrives and Flash Cards are also supported, but they have to be formatted using NTFS. FAT32/exFAT don't support NTFS File Compression.

🟦 Average measured decompression speed for different algorithms
i7-4790K @ 4.4 GHz. Tested on a RAM Disk. Windows 10 build 18363.836. Hollow Knight folder.
Note: the values don't correspond to game load times. In practice, the game can load game data faster on any of the algorithms or rarely even without compression at all, depending on the system performance, disk speed, disk space reduction and the game itself. Testing in practice on individual games and systems is recommended.
LZX: 750 MB/s <— highest size reduction (good for HDD and SATA SSD)
XPRESS16K: 1022 MB/s <— highest read speed for i7-4790K 4C/8T (good for fast NVMe SSD)
XPRESS8K: 983 MB/s
XPRESS4K: 890 MB/s <— the fastest (lightest) algorithm for very slow CPUs
LZNT1 (Old Windows): 573 MB/s <— not optimized for games/programs
.zip file: 204–420 MB/s (depending on compression settings and program used for decompression)

I wrote a simple open source online tool for analyzing your save file to quickly check everything you missed for your Hollow Knight Game Completion Percentage (also includes locations/costs, Achievements Essentials, Game Statistics and a Hint system):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2209910193

I'm creating Deep Learning Neural Network AI 4K/60fps Remastering, Game Videos, Game Audio, Gameplays, Guides and other technology experiments on my youtube channel (Michael ReznoR). For example:
Diablo 2: AI Remastered Widescreen Gameplay 4K 60fps [Sorceress]
Statistics and fun facts from the conversion process:
✅ Creating this video took ~11 days and nights (not counting the whole research period)
✅ 53121 files total
✅ Over 400 GB disk space total
✅ Lots of re-recording the same footage (Diablo boss fight required recording 4 times, guess why)
✅ At least 21 different tools (programs, scripts, plugins, mods) used for making
You may take a look if you're interested.

Guide by rezno[R] ©️® 2020. All rights reserved.
I'm always open for constructive criticism which will improve the guide for everyone.
Huge thank you and admiration to Team Cherry for creating this awesome game.
If I helped you in any way, I will be happy. Have fun playing Hollow Knight! 🧡
If you like, you can support my efforts through PayPal[www.paypal.me].