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There's nothing to trim from PS1 ISOs, The ISO size is the same as the Game's data size.
Trimming is used only on Read Only Memory chipset dump (ROM), because when you dump a chipset you read all "sectors" of the chipset from start to end, whether there are data or not.
Then, trimming means removing the ending part of the resulted dump file where there's no Data (the part after the game's size up to the chipset size, which could be up to 49% removed from the dump).
Chipset are always multiple of 2, so the chipset size are 2, 4, 8, 16, (24 too), 32 etc.
Let's talk in Megabit (chipsets size are always counted in bit not bytes)
If your game is 5Mb, it will not fit in the 4Mb chipset, the manufacturer will use a 8Mb chipset for only 5Mb of game's data.
When you dump the game, you end with a 8Mb file dump, but only 5Mb is used so you can safely "trim" the 3Mb of unused data from that dump, which is (always?) located at the end of the chipset.
If you want to reduce an ISO size, you need to edit the game's content and remove data (like unused languages if the game is multi-5, replace all videos with a dummy/shorter videos, etc.)
PS1 data is not encrypted or signed, you can edit and replace the files with a simple file explorer and make a new ISO.
If you want to reduce the file size for storage purpose only, you should check ecm tool from Neil Corlett :
http://www.neillcorlett.com/ecm/
Trimming is used only on Read Only Memory chipset dump (ROM), because when you dump a chipset you read all "sectors" of the chipset from start to end, whether there are data or not.
Then, trimming means removing the ending part of the resulted dump file where there's no Data (the part after the game's size up to the chipset size, which could be up to 49% removed from the dump).
Chipset are always multiple of 2, so the chipset size are 2, 4, 8, 16, (24 too), 32 etc.
Let's talk in Megabit (chipsets size are always counted in bit not bytes)
If your game is 5Mb, it will not fit in the 4Mb chipset, the manufacturer will use a 8Mb chipset for only 5Mb of game's data.
When you dump the game, you end with a 8Mb file dump, but only 5Mb is used so you can safely "trim" the 3Mb of unused data from that dump, which is (always?) located at the end of the chipset.
If you want to reduce an ISO size, you need to edit the game's content and remove data (like unused languages if the game is multi-5, replace all videos with a dummy/shorter videos, etc.)
PS1 data is not encrypted or signed, you can edit and replace the files with a simple file explorer and make a new ISO.
If you want to reduce the file size for storage purpose only, you should check ecm tool from Neil Corlett :
http://www.neillcorlett.com/ecm/
Sorry for digging up an older thread, but this really intrigues me. Are you saying that I can just open a PS1 ISO with Windows Explorer, delete what I want to delete, make a new ISO from those files using something like ImgBurn, and it will play without error? I used to fill my PSP with PS1 titles I converted but the file size was usually fairly high on some titles. If I could edit the size myself, that'd be awesome! The only thing I've seen similar to that are ROM clippers for DS and ripkits for PSP, but never anything for PS1 titles.
Ripping, before the concept largely died with the likes of the 360 and PS3 having disc checks unbroken by the available methods of hacking, was also a term for removing content as Cyan described as well as the now more common use of dumping a game. The dreamcast and xbox used such techniques extensively and quite a few used them on the DS as well, though aside from some binary compression stuff never that I saw on scene releases for the DS.
Anyway yeah you can, most PS1 and PS2 games used raw iso 9660 as their underlying format. Sadly I have no freeware tools you can rebuild/edit isos with, and if you are dealing in legacy dumps then you will have a whole bunch of formats (clonecd, cdrwin, discjuggler, nero/nrg....) to contend with anyway, so it is something like ultraiso, magiciso or poweriso that you will need to do the deed.
The only other thing of note is raw LBA/DMA/sector level reads. It was variously used as a form of antipiracy and later (and more commonly on the PS2) used to hide data away (Square (Enix) being noted fans of it.
Also deleting might be a bit strong, you might do better to instead relink the files or inject smaller versions of them but deleting also works in many cases.
Edit. Might as well have the old DS ripping thread linked up
http://gbatemp.net/threads/gbatemp-...-rewritten-for-2012.73394/page-2#post-1799596
Anyway yeah you can, most PS1 and PS2 games used raw iso 9660 as their underlying format. Sadly I have no freeware tools you can rebuild/edit isos with, and if you are dealing in legacy dumps then you will have a whole bunch of formats (clonecd, cdrwin, discjuggler, nero/nrg....) to contend with anyway, so it is something like ultraiso, magiciso or poweriso that you will need to do the deed.
The only other thing of note is raw LBA/DMA/sector level reads. It was variously used as a form of antipiracy and later (and more commonly on the PS2) used to hide data away (Square (Enix) being noted fans of it.
Also deleting might be a bit strong, you might do better to instead relink the files or inject smaller versions of them but deleting also works in many cases.
Edit. Might as well have the old DS ripping thread linked up
http://gbatemp.net/threads/gbatemp-...-rewritten-for-2012.73394/page-2#post-1799596
