4.01 M33 by M33=Dark_AleX
===================Requirements
-------------- In order to install 4.01 M33 Firmware you will need the following:
- Either a PSP-100* console (AKA Fat PSP) running either 3.52 M33-3 or 3.52 M33-4 or higher (Previous versions of M33 won't work, due to a bug that affects them and OE) or a PSP-200* (AKA Slim PSP) running 3.60-M33 or higher.
- 4.01 M33 (MIRROR#1 - MIRROR#2) by M33=Dark_AleX
- Official SONY v4.01 Firmware Update EBOOT. Download it from PSP-Hacks.Com [RAR format]
- Official SONY v1.50 Firmware Update EBOOT. This one will ONLY be required if you want to install the 1.50 Kernel compatibility, which is useful ONLY to Classic (Fat) PSPs. If you have a Slim DO NOT even try installing it, it won´t work. Download it from QJ-Net [ZIP Format] or from PSP-Hacks.Com [ZIP Format].
Precautions/Suggestions before you start
--------------------------------------------
- Ensure the memory stick used for the upgrade/downgrade process is in good shape. This means it's got no bad sectors that may result in failed CRC checksums for the files contained in it.
- Normally if your Memory Stick is legitimate you should not have any problems. Many people have experienced semibricks / bricks due to cheap fake and unreliable memory sticks sold on eBay. As a suggestion I recommend you either use the original 1GB memory card bundled originally with your PSP or find out whether your memory stick is legitimate or not before attempting the process.
- A good practice would be formatting the Memory Stick prior to the downgrade (Remember to back your important files up before you do that) and use any error-checking utility to scan the Memory Stick for failures.
- Alternatively you can use a CRC checksum utility (SFV, MD5SUM...) to verify that the data copied onto your memory stick is consistent with the original.
- Charge your battery to its maximum capacity in advance and leave the PSP plugged to the mains during the upgrade/downgrade process.
- During the upgrade/downgrade process, once the files have started being copied to the flash memory you MUST not be reboot your PSP manually, or turn it off, or the remove the Memory Stick until the flashing process has finished, or otherwise your PSP will end up bricked.
- If you are installing either the 4.01 M33 CFW or any of the UPDATE files in a Fat PSP, ensure you have configured in the Recovery Menu of the PSP the GAME folder to run in the 3.XX kernel mode, or otherwise the installer will refuse to run.
Installation
------------1.- Download the 4.01 M33 by M33=Dark_AleX from any of the above link. Uncompress the contents of the downloaded "
401M33.rar" file (The name may differ is you got it from any of the mirrors) into a handy location of your HD. Browse the uncompressed contents in your HD, and you will see a folder called
UPDATE.
2.- Connect your PSP to your PC via USB cable and enable the USB Mode on your PSP.
3.- From your Operative System, go to the directory
:/PSP/GAME located in your memory stick.
4.- Copy the
UPDATE folder and its contents, into the folder
:/PSP/GAME of your Memory Stick.
5.- Download the 4.01 Official SONY Update File from the download link above. Make sure you select a handy location in your Hard Disk where you can find easily it later on, i.e. Your Windows Desktop. The Update EBOOT.PBP file will be packed in RAR Format and you might need some additional software to uncompress the file (for instance WinRAR). Uncompress the RAR file, and you should en up with a uncompressed file named
EBOOT.PBP. This is the uncompressed Firmware Update file. Keep the file in a handy location easy to find in your HD. Alternatively, if you have access to a wireless conexion for your PSP, you can just skip this step and let the PSP connect to the internet and download the update file itself. If you chose this alternative, then just jump onto step 11.
6.- Rename the file
EBOOT.PBP into
401.PBP.
7.- Copy the file
401.PBP to the folder
:/PSP/GAME/UPDATE of your Memory Stick.
Note: The program will not even show in the PSP if you copy it to a different folder than that one.
8.- Disable the USB Mode safely and disconnect the PSP from the PC.
9.- In the PSP's XMB Menu, goto "Game" -> "Memory Stick"
10.- Highlight the 4.01 M33 installer and press the X button to execute the program which will require al least 78% of battery. If you have idstorage corrupted due to a downgrader, the program will ask you to correct it automatically so the update can continue.
11.- Press X, and the Sony updater will begin. Sit and enjoy while Sony code installs 4.01 M33
12.- When finished, the updater will ask you to reboot (pressing X or O). DO SO. Do not skip this step by shutting down the PSP using the On/Off Switch or otherwise you'll end up with a brick.
13.- Restart your PSP. Check your PSP Settigs Menu (Settings -> System Settings -> System Information). You should be now in 4.01 M33
Upgrading your CFW or installing the latest bugfix patch the "new" and easy way
------------------------------------------------------------------------------Dark_Alex has implemented a cool new feature since CFW 3.80 M33, the automatic installer via internet.
If you are currently in 3.80 M33 (or over), just configure a Network Connection so you can browse the internet via WiFi with your PSP. Go to System -> Network Update and press the "X" button. The PSP will connect to the internet and check whether there is a bugfix patch available at
Dark_ALex´s Homepage. If there´s any it will download it for you automatically, and once downloaded it will ask if you want to install it straightaway or otherwise it will tell you to run it via the Game menu.
With this Network Update you can even update from 3.80 M33 (or over) to 4.01 M33, the PSP will even ask you if you want to download the Official SONY v4.01 Firmware Update EBOOT in the process

With this feature you can currently update up to
4.01 M33-2!!
This nice feature is enable by default. You can turn it off in the Recovery Menu (When off, Network Update will download Sony updates as usual). Basically it is an automated install and makes the process even simpler and fool proof. Obviously you need access to a WiFi Hotspot or local WAN at home. If you don´t just carry on reading and do it the "old" way.
Installing the latest bugfix patch the "old" way
------------------------------------------------Currently the latest patch is the
UPDATE #2. Your PSP must be running 4.01 M33 already prior to the installation of this patch. These update patches usually correct bugs identified by users, hence it´s strongly recommended to apply them. They are also cumulative, meaning that the update 5 for instance will contain the bugfixes fromt he Updates 2, 3 and 4 as well, hence no need to install every single one of them in order, just grab the latest and that´s it.
1.- Download the
UPDATE #2.
2.- Uncompress the contents of the "
401M33-2.rar" file into a handy location your HD. Browse the uncompressed contents in your HD, and you will see a folder called
UPDATE.
3.- Connect your PSP to your PC via USB cable and enable the USB Mode on your PSP.
4.- From your Operative System, go to the directory
:/PSP/GAME located in your memory stick.
5.- Copy the
UPDATE folder and its contents, into the folder
:/PSP/GAME of your Memory Stick. If it asks you to overwrite any files, confirm with "Yes".
6.- Disable the USB Mode safely and disconnect the PSP from the PC.
7.- In the PSP's XMB Menu, goto "Game" -> "Memory Stick"
8.- Highlight the M33 Updater and press X button to execute the program.
9.- Press X, and the Update will be installed.
10.- Check your PSP Settigs Menu (Settings -> System Settings -> System Information). You should be now in 4.01 M33-2
Installing the 1.50 Kernel compatibility (FOR FAT PSPs ONLY)
---------------------------------------------------------------Since the Slim PSP is not compatible with 1.50 Kernel the main CFW installer will not install 1.50 Kernel anymore. Nevertheless a 1.50 Kernel addon for 4.01 M33 is available to add this capability (but for Fat PSPs ONLY). Therefore if you have a Slim PSP you must skip this section.
Note: This update is totaly independent of the 4.01 M33 version installed (1 or future ones).
1.- Download the
1.50 Kernel addon for 4.01.
2.- Uncompress the contents of the "
150k_addon401.rar" file into a handy location your HD. Browse the uncompressed contents in your HD, and you will see a folder called "
150k_Addon" containing four files (EBOOT.PBP, ipl_update.prx, libpsardumper.prx and pspdecrypt.prx).
3.- Connect your PSP to your PC via USB cable and enable the USB Mode on your PSP.
4.-Copy the folder called "
150k_Addon" and all its contents to
ms0:/PSP/GAME4xx/5.- Download the 1.50 Official SONY Update File from any of the download links above. Unzip the 1.50 update to a temporary folder. Rename the unzipped 1.50
EBOOT.PBP file to
150.PBP. Then copy it into the root of your Memory Stick.
6.- Disable the USB Mode safely and disconnect the PSP from the PC.
7.- In the PSP's XMB Menu, goto "Game" -> "Memory Stick"
8.- Highlight the 1.50 Kernel Installer for 4.01 M33 and press X button to execute the program.
9.- The updater will remind you that once installed you will loose the Location Free Player and Korean font. Press X to agree, and the Update will be installed.
20.- Your fat PSP will now be able to execute homebrew applications based in 1.50 Kernel. (Remember that by default all 1.50 Kernel Homebrew should be installed in the
:/PSP/GAME150/ folder).
Changes in 4.01 M33
--------------------- Now uses 4.01
- Bug fix: vshmenu didn't let change camera mode due to camera_plugin using select button. Fixed, now vsh menu will not be loaded when using the camera.
- Recovery can now be translated. Check readme.txt within 401M33.rar file to find out how. Translation to spanish is autoincluded.
- pdated the M33 SDK with a new function and sample, and released the psp-packer tool to compress prx's and PBP's in the ~PSP format.
- The folder of 4.01 and highre homebrew will be GAME4XX so it won't need change on update
Basically these are the Original CFW / UPDATE / 150 ADDON Instructions from the ReadMe.txt with a few additions / changes to make it more understandable.
If you have read the instructions but you are still having trouble to get the CFW installed working, we suggest that you reply to this topic with the question(s) that you may have rather than starting a new topic/thread instead. We'll try to help

.
Hopefully this guide will stop unnecessary threads from people asking the same questions again and again.
It goes without saying that any replies asking or discussing about ISO capabilities of any sort will be automatically deleted. O:-)
Credits to:
Dark_ALeX