Editing Bios

== Content ==

Here is an overview of what is contained in a PS2 ROM (including TOOL, DESR/PSX, ps2emu/ps2gxemu/ps2softemu (PS3), System 246 and System 256).
This list isn't finished yet, so add your comments below!

{| class="wikitable" style="font-size:small;"
|-
! File !! Description !! Remarks
|-
| ACDEV || Arcade ROM device service. || 
|-
| ADDDRV || Adds support for the DVD ROM (rom1:), via ROMDRV. || 
|-
| ADDROM2 || Adds support for rom2 (which contains a Chinese font file), only for Chinese consoles (SCPH-50009). || 
|-
| APPLOAD || || 
|-
| ATAD || The DEV9+ATAD(+Flash device) combo driver. First appearing in ROM v1.10. Has no support for the CXD9566R. Despite its similar name, it is very different from the full ATAD module. || 
|-
| BNNETCNF || not entirely sure what this is for, but it appears in the PS3's PS2 ROMs. Seems to be for network configuration, but why? || 
|-
| BOARDINF || reads in the DSW602 board's ID and sets up the values for Boot Modes 6 and 7. Only does something useful on TOOL units. || 
|-
| BTNB01 || || 
|-
| BUILD || || 
|-
| CDVDFSV || The RPC server for CDVDMAN. || 
|-
| CDVDMAN || The CD/DVD manager. || 
|-
| CLEARSPU || Seems to clear/reset the SPU, but is known to cause crashes under some conditions. Not sure if it's buggy or not. Only used by the OSDSYS of the SCPH-10000 and SCPH-15000, probably retained for backward-compatibility. || 
|-
| CMN01 || || 
|-
| CMN02 || || 
|-
| D2ELOADP || DECI2 ELOADP extension (ERX module support). || 
|-
| DAEMON || || 
|-
| DBCMAN || || 
|-
| DECI1 || DECI1 manager. Purpose of its existence is not known. || 
|-
| DECI1DR1 || DECI1 H1500 driver. Purpose unknown. || 
|-
| DECI1DRP || DECI1 PIF/mini-RA driver. Purpose unknown. || 
|-
| DECI2 || DECI2 manager. || 
|-
| DECI2DRP || DECI2 PIF driver || 
|-
| DECI2DRS || DECI2 SIF2 driver. || 
|-
| DECI2FILE || DECI2 host (and TTY) driver. || 
|-
| DECI2HSYN || DECI2 Host SYNchronization driver. Notifies the DECI2 manager when the host interface (i.e. PIF) is up. || 
|-
| DECI2KPRT || DECI2 KTTY driver. || 
|-
| DECI2LOAD || DECI2 IOP module loader. || 
|-
| DECKARD || The SCPH-7500x has a newer PowerPC processor in place of the IOP, and requires code to emulate the IOP. || 
|-
| DMACMAN || DMA Controller Manager. || 
|-
| DVDCNF || Contains IOP boot configuration file for the DVD player. || 
|-
| DVDELF || DVD player executable for expansion-bay consoles. || 
|-
| DVDID || DVD player ID. SCPH-70000 (ROM v2.00) and later had universal DVD ROMs, hence the existence of DVDID* files for each region. || 
|-
| DVDIDA || || 
|-
| DVDIDC || || 
|-
| DVDIDE || || 
|-
| DVDIDJ || || 
|-
| DVDIDM || || 
|-
| DVDIDO || || 
|-
| DVDIDR || || 
|-
| DVDIDU || || 
|-
| DVDPLA || DVD player executable for slimlines. SCPH-70000 (ROM v2.00) and later had universal DVD ROMs, hence the existence of DVDPL* files for each region. || 
|-
| DVDPLC || || 
|-
| DVDPLE || || 
|-
| DVDPLJ || || 
|-
| DVDPLM || || 
|-
| DVDPLO || || 
|-
| DVDPLR || || 
|-
| DVDPLU || || 
|-
| DVDVER || DVD player version number. SCPH-70000 (ROM v2.00) and later had universal DVD ROMs, hence the existence of DVDVER* files for each region. || 
|-
| DVDVERA || || 
|-
| DVDVERJ || || 
|-
| DVDVERR || || 
|-
| EECONF || Loads part of the system configuration from the MECHACON EEPROM. Also configures and resets some peripherals, depending on the model version. In slimlines, EECONF will also load the MAC address. || 
|-
| EELOAD || The EE ELF loader, which is loaded by LoadExecPS2() to 0x00082000 for loading ELFs. || 
|-
| EELOADCNF || Contains the IOP boot configuration file for EELOAD. || 
|-
| EENULL || The idle thread (id #0) module, loaded to 0x00081FC0. || 
|-
| EESYNC || For synchronizing with the EE, at the end of IOP resets. EESYNC from DNAS images are evil; they also perform a memory wipe of the region from 0x00084000 to .0x00100000. || 
|-
| EROMDRV || Encrypted ROM DRIver for the expansion-bay PlayStation 2 sets. || 
|-
| EROMDRVA || Encrypted ROM DRIver for the SCPH-70000 (ROM v2.00) and later PlayStation 2 sets. || 
|-
| EROMDRVC || || 
|-
| EROMDRVE || || 
|-
| EROMDRVJ || || 
|-
| EROMDRVM || || 
|-
| EROMDRVO || || 
|-
| EROMDRVR || || 
|-
| EROMDRVU || || 
|-
| ESDATA || || 
|-
| EXCEPMAN || Exception manager. || 
|-
| EXTINFO || Contains the "EXTINFO" for all files in the ROM image. || 
|-
| FILEIO || RPC server for IOMAN. Sony has greatly changed the semantics and design of FILEIO after some point. Connecting an old FILEIO EE RPC client to a newer server will result in a severe IOP crash. || 
|-
| FNTASCII || || 
|-
| FNTEX000 || || 
|-
| FNTEX001 || || 
|-
| FNTEXOSD || || 
|-
| FNTIMAGE || Contains fonts for the OSDSYS of the SCPH-18000 and newer. || 
|-
| FONTM || The FONT Module, used by the OSDSYS. || 
|-
| FONTS || || 
|-
| GB18030 || Chinese FONT module, replace FONTM. Loaded from rom2: on SCPH-50009 || On PS2 that use it, this file is required to boot at all. 
|-
| HDDLOAD || Update loader for the HDD unit (and later includes the flash device). || 
|-
| HDDOSD || Not sure what this does, but it is present in the expansion-bay ROMs. || 
|-
| HEAPLIB || Memory HEAP LIBrary (i.e. thvpool, thfpool). || 
|-
| HLPB01 || || 
|-
| HLPB02 || || 
|-
| HLPB03 || || 
|-
| HLPB04 || || 
|-
| HLPB05 || || 
|-
| HLPB06 || || 
|-
| HLPB07 || || 
|-
| HLPB08 || || 
|-
| HLPB09 || || 
|-
| HLPB10 || || 
|-
| HLPB11 || || 
|-
| HLPB12 || || 
|-
| HLPB13 || || 
|-
| HLPB14 || || 
|-
| ICOBCDDA || || 
|-
| ICOBDISC || || 
|-
| ICOBDVDD || || 
|-
| ICOBFBRK || || 
|-
| ICOBFNOR || || 
|-
| ICOBFSCE || || 
|-
| ICOBPKST || || 
|-
| ICOBPS1D || || 
|-
| ICOBPS1M || || 
|-
| ICOBPS2D || || 
|-
| ICOBPS2M || || 
|-
| ICOBQUES || || 
|-
| ICOBYSYS || || 
|-
| ICOIMAGE || Contains icons for the OSDSYS of the SCPH-18000 and newer. || 
|-
| IGREETING || Displays boot information (i.e. IOP boot type, EBOOTP, IBOOTP, switch positions for DSW602 and the type of DSW602 board installed). || 
|-
| ILINK || i.Link driver || present in only the arcade ROMs. 
|-
| ILSOCK || i.Link socket driver || present in only the arcade ROMs. 
|-
| INTRMANI || Interrupt Manager. According to wisi, it is for IOP mode. || 
|-
| INTRMANP || Interrupt Manager. According to wisi, it is for PS mode. Never used. || 
|-
| IOMAN || I/O Manager. || 
|-
| IOPBOOT || IOP bootup program. || 
|-
| IOPBTCON2 || Boot configuration file for the IOP, for the first phase of the IOP reset (before UDNL is loaded). || 
|-
| IOPBTCONF || Boot configuration file for the IOP, during the final phase of the IOP reset. If no UDNL module is specified, the IOP will only have a single IOP reset in the reboot process, with the modules listed in IOPBTCONF. || 
|-
| KERNEL || The EE kernel. || 
|-
| KROM || Kanji ROM? Not sure where this is used. || 
|-
| KROMG || || 
|-
| LED || || 
|-
| LGBB01 || || 
|-
| LGBB02 || || 
|-
| LGBB03 || || 
|-
| LGBB04 || || 
|-
| LGBB05 || || 
|-
| LIBFI || This is not present in the boot ROM of the SCPH-10000 and SCPH-15000. || 
|-
| LIBSD || Sound driver library. || 
|-
| LOADCORE || The core of IOP module loading. Provides the lowest level of IOP module loading functions. Also handles the startup of the IOP. || 
|-
| LOADFILE || The RPC server for MODLOAD. || 
|-
| LOGO || PS1 logo? || 
|-
| MBROWS || Only used by the old OSDSYS program from ROM v1.00 and v1.01. || 
|-
| MCLOCK || Only used by the old OSDSYS program from ROM v1.00 and v1.01. || 
|-
| MCMAN || Memory Card Manager. || 
|-
| MCMANO || MCMAN (Open?). Present in the System 246 ROM. Has support for the regular PlayStation 2 Memory Cards, while the System 246's MCMAN module only supports the arcade dongle. || 
|-
| MCSERV || RPC server for MCMAN. || 
|-
| MODLOAD || IOP module loader. || 
|-
| MOPEN || Only used by the old OSDSYS program from ROM v1.00 and v1.01. || 
|-
| MSGB01 || || 
|-
| MSGB02 || || 
|-
| MSGB03 || || 
|-
| MSGB04 || || 
|-
| MSGB05 || || 
|-
| MSGB06 || || 
|-
| MSGB07 || || 
|-
| MSGB08 || || 
|-
| MSGB09 || || 
|-
| MSGB10 || || 
|-
| MSGB11 || || 
|-
| MSGB12 || || 
|-
| MSGB13 || || 
|-
| MTAP || || 
|-
| NCDVDMAN || It is a strange abomination that was introduced and used with only the SCPH-70000 series, so it was probably provided for backward-compatibility. It seems to be a heavily stripped-down CDVDMAN module, with no support for some S-command functions like sceCdRI. I don't know why this was done, but it might be a deliberate move by Sony to prevent hackers from using these system functions. Didn't really do anything, however. || 
|-
| NUMB01 || || 
|-
| NUMB02 || || 
|-
| NUMB03 || || 
|-
| NUMB04 || || 
|-
| NUMB05 || || 
|-
| OLDROM || Contains a subset of ROM modules that are required for the late TOOL ROM to provide DEX-like functionality (i.e. old ROM modules). || 
|-
| OSBROWS || Used by the old OSDSYS program from ROM v1.00/v1.01. || 
|-
| OSCLOCK || Used by the old OSDSYS program from ROM v1.00/v1.01. || 
|-
| OSDCNF || Contains the IOP boot configuration for OSDSYS (mainly listing the X prefixed modules) || 
|-
| OSDSND || OSD sound library. This is actually the tentative sound driver, which is called "librspu2" in the Sony SDK. The funny thing about OSDSND from the SCPH-18000 and newer is that it's newer than the one in the Sony SDK, even at release v3.02. || 
|-
| OSDSYS || The browser. || 
|-
| OSDVER || Seems to be a build number for the OSD. || 
|-
| OSFONTM || Used by the old OSDSYS program from ROM v1.00/v1.01. || 
|-
| OSFONTS || Used by the old OSDSYS program from ROM v1.00/v1.01. || 
|-
| OSOPEN || Used by the old OSDSYS program from ROM v1.00/v1.01. || 
|-
| PADMAN || Pad manager. || 
|-
| PADMAN2 || || 
|-
| PATAD || ATAD module for DESR systems used in its OSDSYS program. || 
|-
| PCDVDFSV || CDVDFSV module for DESR systems used in its OSDSYS program. || 
|-
| PCDVDMAN || CDVDMAN module for DESR systems used in its OSDSYS program. || 
|-
| PDEV9 || DEV9 module for DESR systems used in its OSDSYS program. || 
|-
| PEESYNC || EESYNC module for DESR systems used in its OSDSYS program. || 
|-
| PFILEIO || FILEIO module for DESR systems used in its OSDSYS program. || 
|-
| PFLASH || FLASH module for DESR systems used in its OSDSYS program. || 
|-
| PFLSLOAD || Flash load module for DESR systems used in its OSDSYS program. || 
|-
| PHDD || TIMEMAN module for DESR systems used in its OSDSYS program. || 
|-
| PHDDLOAD || HDDLOAD module for DESR systems used in its OSDSYS program. || 
|-
| PIOMAN    || IOMAN module for DESR systems used in its OSDSYS program. || 
|-
| PIOPRP    || IOPRP 3.1.0 used for the PS3 ps2_emu OSDSYS program. || 
|-
| PLIBSD    || LIBSD module for DESR systems used in its OSDSYS program. || 
|-
| PLOADCORE || LAODCORE module for DESR systems used in its OSDSYS program. || 
|-
| PLOADFILE || LOADFILE module for DESR systems used in its OSDSYS program. || 
|-
| PMCMAN    || MCMAN module for DESR systems used in its OSDSYS program. || 
|-
| PMCSERV   || MCSERV module for DESR systems used in its OSDSYS program. || 
|-
| PMODHSYN  || MODHSYN (part of CSL) module for DESR systems used in its OSDSYS program. || 
|-
| PMODLOAD  || MODLOAD module for DESR systems used in its OSDSYS program. || 
|-
| PMODMIDI  || MODMIDI module (part of CSL) for DESR systems used in its OSDSYS program. || 
|-
| PMODSESQ  || MODSESQ module (part of CSL) for DESR systems used in its OSDSYS program. || 
|-
| PMTAPMAN  || MTAPMAN module for DESR systems used in its OSDSYS program. || 
|-
| POWEROFF  || || 
|-
| PPADMAN   || PADMAN module for DESR systems used in its OSDSYS program. || 
|-
| PRMMAN2   || RMMAN2 module for DESR systems used in its OSDSYS program. || 
|-
| PROMDRV   || ROMDRV module for DESR systems used in its OSDSYS program. || 
|-
| PS1DRV || The PlayStation driver. Sets up the EE for GPU emulation and resets the IOP into PS1 mode. || 
|-
| PS1ID || Only found in newer boot ROMs || 
|-
| PS1VER || || 
|-
| PS1VERA || || 
|-
| PS2LOGO || Displays the PlayStation 2 logo from the inserted disc. For newer consoles, if the logo cannot be decrypted properly, it will fall back to the browser. Not actually required to boot games, but the Sony OSDSYS boots PS2 games through this program. || 
|-
| PSDRDRV    || SDRDRV module for DESR systems used in its OSDSYS program. || 
|-
| PSIFCMD    || SIFCMD module for DESR systems used in its OSDSYS program. || 
|-
| PSIFMAN    || SIFMAN module for DESR systems used in its OSDSYS program. || 
|-
| PSIO2MAN   || SIO2MAN module for DESR systems used in its OSDSYS program. || 
|-
| PSTDIO     || STDIO module for DESR systems used in its OSDSYS program. || 
|-
| PSXVER     || Version of the ROM for DESR system. || 
|-
| PSYSCLIB   || SYSCLIB module for DESR systems used in its OSDSYS program. || 
|-
| PSYSMEM    || SYSMEM module for DESR systems used in its OSDSYS program. || 
|-
| PTHREADMAN || THREADMAN module for DESR systems used in its OSDSYS program. || 
|-
| PTIMEMANI  || TIMEMAN module for DESR systems used in its OSDSYS program. || 
|-
| PXATAPI || ATAPI driver for the (the DVD writer of the) PSX. TXATAPI is used by TESTMODE of the PSX. || 
|-
| PXFROMMAN || Dev9 flash filesystem driver for DESR systems used in its OSDSYS program. || 
|-
| RDRAM || Provides a RDRAM test for the EE at power-on. This is run from RESET. || 
|-
| RDRAM1 || || 
|-
| RDRAM2 || || 
|-
| REBOOT || The reboot service. Receives IOP reset packets from the EE, from across the SIF. || 
|-
| RESET || Bootstrap code for the EE and IOP. || 
|-
| RMMAN || ReMote-con MANager for the external IR receiver. || 
|-
| RMMAN2 || ReMote-con MANager for the internal IR receiver (SCPH-50000 and later). || 
|-
| RMRESET || ReMote controller reset. || 
|-
| ROMDIR || The ROMDIR part of the ROM image. || 
|-
| ROMDRV || ROM driver. Provides access to the boot ROM (rom0). || 
|-
| ROMGSCRT || First appeared in ROM 1.60. Provides a portable method for manipulating GS screen modes. The SCPH-10000 and SCPH-15000 do not have this. || 
|-
| ROMVER || ROM version. || 
|-
| SBIN || PS1 BIOS kernel memory COFF file. This is loaded into kernel memory at 0x80000500 (-0x90 header), and contain A0/B0/C0 vector handlers, and more. On real PS1 this code is located at 0xBFC10000, and later also copied to 0x80000500 during bios initialization. || 
|-
| SDRDRV || Library for allowing the EE to remotely access the SPU2 via libsd. || 
|-
| SECRMAN || Security Manager. Signing is NOT done with the one in ROM, but with a special version that comes with the utility discs. Debug stations , TOOL, and PS3 units have a different SECRMAN module from retail sets. || 
|-
| SIFCMD || SIF command module. Contains the SIF command and SIF RPC functions. ||
|-
| SIFINIT || Initializes the SIF. || 
|-
| SIFMAN || SIF manager. ||
|-
| SIO2D || || 
|-
| SIO2MAN || SIO2 manager. Provides access to the SIO2 interface. || 
|-
| SNDBOOTB || ||
|-
| SNDBOOTH || || 
|-
| SNDBOOTS || ||
|-
| SNDCLOKS || || 
|-
| SNDIMAGE || Sound image. Contains sounds for the OSDSYS of the SCPH-18000 and newer. || 
|-
| SNDLOGOS || ||
|-
| SNDOSDDB || ||
|-
| SNDOSDDH || || 
|-
| SNDRCLKS || || 
|-
| SNDTM60S || || 
|-
| SNDTNNLS || || 
|-
| SNDWARNS || || 
|-
| SSBUSC || SSBUS Controller library. The SSBUS seems to be the bus that all peripherals get connected to. It seems to have the power to control the mapping of the device registers, as well as access timing. || 
|-
| SSDATA || || 
|-
| SSND || || 
|-
| STDIO || Standard I/O library. || 
|-
| SYSCLIB || System C Library. || 
|-
| SYSMEM || System Memory Manager. || 
|-
| TBIN || PS1 BIOS. This is started by RESET, when the IOP is in PS1 mode. || 
|-
| TDEV9 || Dev9 driver for the DESR used in TESTMODE. || 
|-
| TDVRDRV || DVR Driver for the DESR used in TESTMODE. || 
|-
| TDVRMISC || Miscellaneous DVR functionality driver for the DESR used in TESTMODE. || 
|-
| TESTMODE || Test mode program. The EE will boot this module from EELOAD, if the console is put into service mode by the SONY service jig. For expansion bay sets, it is a device that goes into the expansion bay, but connects to the chassis from within it (it does not connect to the expansion connector). || 
|-
| TESTSPU || Used by the TESTMODE program for testing the SPU. || 
|-
| TEXBARRW || || 
|-
| TEXBBTTN || || 
|-
| TEXBCDPB || || 
|-
| TEXBCPAR || || 
|-
| TEXBICHI || || 
|-
| TEXBNAV1 || || 
|-
| TEXBNAV2 || || 
|-
| TEXBOVAL || || 
|-
| TEXCBINV || || 
|-
| TEXCBLUR || || 
|-
| TEXCBUMP || || 
|-
| TEXCFLOW || || 
|-
| TEXCKABE || || 
|-
| TEXCKLFN || || 
|-
| TEXCKLFP || || 
|-
| TEXCKLGN || || 
|-
| TEXCKLGP || || 
|-
| TEXCMARU || || 
|-
| TEXCNAVI || || 
|-
| TEXCREFA || || 
|-
| TEXCSMOK || || 
|-
| TEXCSTSL || || 
|-
| TEXIMAGE || Texture image. Contains textures for the OSDSYS of the SCPH-18000 and newer. || 
|-
| TEXOBLP   || || 
|-
| TEXOBLPR  || || 
|-
| TEXOCRBL  || || 
|-
| TEXOCRLE  || || 
|-
| TEXOFLAR  || || 
|-
| TEXOFOG0  || || 
|-
| TEXOFOG1  || || 
|-
| TEXOFOG2  || || 
|-
| TEXOFOG3  || || 
|-
| TEXOFOG4  || || 
|-
| TEXOPNGD  || || 
|-
| TEXOPNGE  || || 
|-
| TEXOPNGF  || || 
|-
| TEXOPNGG  || || 
|-
| TEXOPNGI  || || 
|-
| TEXOPNGP  || || 
|-
| TEXOPNGS  || || 
|-
| TEXOREF   || || 
|-
| TEXOSCE   || || 
|-
| TEXOWAL0  || || 
|-
| THMON || Simple THread MONitor. Exists only in the late TOOL's ROM. || 
|-
| THPERF  || || 
|-
| THREADMAN || IOP thread manager. || 
|-
| TIMEMANI || Timer Manager (IOP mode) || 
|-
| TIMEMANP || Timer Manager (PS mode) || 
|-
| TIOPIMG || IOPRP 2.8.0x used in DESR TESTMODE. || 
|-
| TPADMAN || PADMAN used in DESR TESTMODE. || 
|-
| TSIO2MAN || SIO2MAN used in DESR TESTMODE. || 
|-
| TXATAPI || ATAPI driver for the (the DVD writer of the) PSX. TXATAPI is used by TESTMODE of the PSX. || 
|-
| TZLIST || Timezone list, used by the OSD. Not present in the SCPH-10000 and SCPH-15000, which only saw a Japan-only release. || 
|-
| UDFIO || UDF driver used by the DVD Player. || 
|-
| UDNL || SilverBull calls this an UpDate DownLoader. Basically, it is responsible for selecting the modules and starting the IOP, during the final phase of the IOP reset where the desired modules are to be loaded into the IOP. || 
|-
| USBD || USB driver, which shows up in System 2x6 systems. || 
|-
| VBLANK || V-Blank management. || 
|-
| VERSTR || Version string. I think that the PS1 ROM will use this because I learned that this string is also present in PlayStation consoles. || 
|-
| XCDVDFSV || CDVDFSV module used in OSDSYS. || 
|-
| XCDVDMAN || CDVDMAN module used in OSDSYS. || 
|-
| XDEV9 || A cut down version of DEV9 used in OSDSYS. || 
|-
| XDEV9SERV || A RPC service for accessing the DEV9 driver directly. Presumably to obtain things like the MAC address. || 
|-
| XFILEIO || FILEIO module used in OSDSYS. || 
|-
| XFLASH || dev9 flash module used in OSDSYS. || 
|-
| XFROMMAN || dev9 flash filesystem module used in OSDSYS. || 
|-
| XLOADFILE || LOADFILE module used in OSDSYS. || 
|-
| XMCMAN || MCMAN module used in OSDSYS. || 
|-
| XMCSERV || MCSERV module used in OSDSYS. || 
|-
| XMTAPMAN || Multi-Tap Manager. XMTAPMAN is used by the expansion bay OSDSYS program. || 
|-
| XPADMAN || PADMAN module used in OSDSYS. || 
|-
| XPARAM || Updated module. File store per title ID settings. OSDSYS call XPARAM to check ID list for currently executed game/app. If ID is found on list, settings/flags are applied. || 
|-
| XPARAM2 || Updated module that seems to be used only in PS3. File store per title ID settings. OSDSYS call XPARAM2 to check ID list for currently executed game/app. If ID is found on list, settings/flags are applied. || 
|-
| XRMMAN2 || Module handling the IR sensor controlled by the Mechacon, used in OSDSYS. || 
|-
| XSHA1 || this only present in PS3. It is used as additional antipiracy check. It seems that it calculate disc main elf checksum and compares it with some database. ||
|-
| XSIFCMD || SIFCMD module used in OSDSYS. ||
|-
| XSIO2MAN || SIO2MAN module used in OSDSYS. || 
|}
Description source: https://gist.github.com/uyjulian/25291080f083987d3f3c134f593483c5

== Boot Process ==
Since ROM is mapped for both IOP and EE reset vectors at the same address (0xBFC00000), Sony implements cpu detection based on PRid COP0 register value. First thing executed by either IOP or EE is MFC0 fetching PRid and performing check if ID is 0x58 or lower, if true, r3000 code will run (branch to 0xBFC02000), otherwise r5900 code is executed (branch to 0xBFC00800). From there both cpus perform respective tasks with code compatible to cpu architecture they run already. IOP code performs few tasks like clearing caches and setting up them depending on if it is PS1/PS2 mode. Now checks 0xBF801450 bit 3 again for PS1/PS2 mode detection, and search in ROM for either IOPBOOT or TBIN and jump to execution of one of those files. TBIN is real PS1 rom, and from time when it is executed r3000 side acts like PS1 CPU. Worth to note that r3000 side of PS2 ROM perform additional check for PRid 0x0F or lower (real PS1) and jumps to TBIN without 0xBF801450 bit 3 PS1/PS2 mode detection. Which suggest that if we flash first 512KB of PS2 rom into PS1, hardware should be functional to at least run games.

== Known Issues ==
=== Flush Cache t5/t6 corruption ===
PS1 mode FlushCache (A0:44) is altered comparing to one from PS1 bios. New version disables DMA by zero write to DCPR for the time when function run. This isn't issue per se, but to do that function use registers t5 and t6. While temp registers should be preserved by caller if needed, there is at least 1 game that rely on them to stay intact after returning from FlushCache. Mortal Kombat Trilogy (NTSC-U). This affect every PS2 model, also PS3 emulators since they use stripped PS2 bios to run PS1 games. Solution: On PS2 patch game image, on PS3 either patch game image or bios itself.