Umm... what system do you have in mind? PS1 does not have USB ports, so that's out of the question. PS2 has USB ports, but can only load PS2 games in that fashion. Furthermore it is limited to USB 1.1, even slower than PS2 DVD drive speed. PS2 games will stutter/slowdown if loaded in this fashion.
I've searched it before and I believe it is impossible to get PS1 off USB. I'm very rusty on it but a tutorial on Open PS2 Loader should explain playing off USB
The reason it wouldn't work with the PS2 is very simple, but also technical. In a traditional, phat ps2, the controller chip that is responsible for the usb/firewire ports is in fact the same CPU (along with 2MB RAM) that ran the PS1. When a PS1 disc is inserted, the bootloader does some funky logic that turns off the EE and uses the GS for handling graphics, since the PS2's GS supercedes everything that the original PS1's graphics chip could do. It then is running off its MIPS chip for the primary. So, by that, ps1 games off usb on a ps2 won't work because the EE is turned off, along with the USB ports, for that compatibility. I can't exactly explain it for the neutered slim PStwo, since that one migrates everything to the EE, and melds the EE and GS together in the same silicon package... but I can only imagine that (with as lazy $ony is) they would engineer the revised hardware to behave similarly. The software emulation for PS1 on a PS3 is the same, but is more accurate largely because the PS3 is so much more powerful to be able to handle things better. PS2 off external is not possible unless you maybe have a BC model in the first place... but PS1 should be more likely.
As far as I know Sony never removed PS1 CPU from PS2 Slim. That chip is responsible for PS1 BC, DVD drive, Ethernet port, and USB ports I/Os.
It was my understanding, and knowledge, that as a cost-cutting measure for the PStwo slim (opposed to the PS2 proper), Sony... Axed off the MIPS chip and relegated its functionality into the revised EE/GS singular chip Which in turn moved PS1 BC on a PS2 from full hardware to software... And because PS1 games played slow or glitchy at the original clock speed... ... the EE was overclocked to compensate Which introduced a lot of errata that included breaking a lot of high profile games, like Final Fantasy VII on PS1, and even PS2 games that had used some undocumented functionality or really strained the PS2 silicon, like how infamously the first release of the PStwo slim could barely play GTA San Andreas, if it could even play it at all. Most video capture shots I'd seen from users at the time showed awful graphics corruption, if the game could even start in the first place.
Some changes were indeed made to the design, but the backwards compatibility was never full-on hardware as not all games were compatible with the PlayStation 2. I'm assuming that the reason why PS1 games cannot be loaded from the HDD bay or from USB is because the hardware that controls those peripherals is simply busy pretending to be PS1 hardware, making the matter pretty tricky. This is why ps2psxe was developed, which is hardly an ideal solution, but it does the job in some cases. If you have any resources on what changes were made in revisions of the motherboards, I'd love to have a read codezer0 - that'd shed some light on the matter. tl;dr The only way to get USB/HDD loading to work is to use ps2psxe and emulate the PS1 which is hit and miss - some games will work perfectly fine, some will chug or glitch. Go on ahead and experiment with that as it's your only non-disc-based solution.
Do you have any factual source on this? Everywhere I read PS2 Slim still carries original PS1 CPU as I/O processor. You are the only one who claimed Sony removed the chip on PS2 Slim. Furthermore I can play FFVII just fine on my SCPH-79001. PS1 game played on PS2 does not upscale, still rendered at 240p. And what is this GTA San Andreas problem on PS2 Slim? I know a lot of people have this problem, not just PS2 Slim, but PS2 FAT too. Many occasion their problems comes down to scratched disc or lens. Like Foxi4 have said though, even original PS2 FAT have problem with some PS1 titles, despite much of the hardware from PS1 was included. Same thing with PS3 FAT, despite EE and GS chips PS2 were included, some PS2 games do have glitches. http://en.wikipedia.org/wiki/List_o...ompatible_PlayStation_2_and_PlayStation_games
I'll try finding it again, but I can't count on it... my google-fu isn't the best, and the site was linked on a site meant for a now-defunct modchip, so it might be lost in internet history. I just know I haven't seen one with the same kinda depth as this one for the PS1 in quite a while. One thing I do remember pretty well with the slimline model was the fact that despite the obvious physical inability to install a hard drive internally, someone enterprising enough with electronics found the connectors to plug a hard drive in were still responding... but the whole process to re-enable that functionality required the installation of a DMS4 Pro, which already had an obnoxious amount of soldering needed to be done.
Only earliest PS2 Slim, SCPH-7000x, has IDE circuitry left behind that Sony forgot to remove. In that instance you can solder an IDE connector and it'll behave like a PS2 FAT HDD. For all other Slims, you have HD Pro which requires to be used in addition to a modchip. In this instance HDD operates more like an ODE that PS2 FAT HDD. You cannot play FFXI in this way, because from PS2 perspective it doesn't see the HDD. DMS4Pro is solderless, but the least reliable modchip for PS2.
You can have it be full on hardware and still not achieve 100% perfect compatibility. Hell, sometimes a certain hardware revision won't even work with some older games right on that same system. But PS2 definitely uses PSX hardware, not software, to do BC. PS3 on the other hand does PSX BC in software, and it's a quite noticeable difference in how it comes out unlike when you compare a PS2 to a PS2 slim (which come out identically in my experience).
