Introduction
This is a free tool for converting one CD image format (Bin) to another format (ISO). The conversion routine is very simple. Just read the Bin image and according to it's structure, write the data in another format. For this reason, a developer must know structure of both formats.
Image Formats
The CD-ROM specification (Yellow Book) defines the use of two types of sectors, mode 1 and mode 2. Mode 2 sectors are used for CD-ROM XA formats.
CD-ROM Sectors
Data stored on a CD-ROM disc is divided into sectors which are equivalent to the audio frames for a CD audio disc. At normal (1x) playback speed, 75 sectors are read every second. For double speed CD-ROM drives this increases to 150 sectors per second and so on. Seek times, while the disc rotates to the required starting position, will also reduce as speeds increase.
Because CDs were designed primarily for audio, their use for computer data requires the addition of header data and error correction codes which are included in every sector. There are two different types of sectors defined in the CD-ROM specification, Mode 1 and Mode 2 (the latter being used for CD-ROM XA discs).
Mode 1 Sectors
Mode 1 sectors are intended for the storage of computer data and contain the following fields.
- Sync (12 bytes) which is used to enable the player to identify the start of each sector.
- Header (4 bytes) consisting of Minutes, Seconds, Sectors and Mode (= 1).
- ECC (Error Correction Code - 276 bytes), which comprises an additional level of CIRC error protection.
- EDC (Error Detection Code - 4 bytes) for detecting errors to be corrected.
Mode 1 sectors are the simplest type and are used for most CD-ROM based formats which follow the Yellow Book.
Mode 2 Sectors
Mode 2 sectors are used for those formats based on CD-ROM XA and can be either Form 1 or 2.
- Mode 2 Form 1 sectors contain 2048 bytes with the same ECC as Mode 1 sectors.
- Mode 2 Form 2 sectors contain 2324 bytes of user data per sector, with no ECC are are suitable only for data where errors can be concealed (eg audio or video data).
Mode 2 sectors comprise the following fields:
- Sync (12 bytes) which is used to enable the player to identify the start of each sector.
- Header (4 bytes) consisting of Minutes, Seconds, Sectors and Mode (= 1).
- Subheader (8 bytes) contains content related parameters eg data type.
- ECC (Error Correction Code - 276 bytes) which comprises an additional level of CIRC error protection for Form 1 only.
- EDC (Error Detection Code) for Forms 1 and 2.
Note that Mode 1 and Mode 2 Form 1 use the same error correction so can be used interchangeably, but not within the same track and preferably not on the same disc. Software used to write CD-Rs can be set for Mode 1 or Mode 2 Form 1. Almost all PCs and Macs will read Mode 2 Form 1 CD-ROMs as well as Mode 1.
Note that any CD-ROM will contain at least some Mode 1 or Mode 2 Form 1 sectors.
Capacity
The capacity of a CD-ROM depends on whether it is a Mode 1 CD-ROM or Mode 2 CD-ROM XA. Assuming the maximum size is 76 minutes 30 seconds (as recommended) this means that there are 336,300 sectors on a CD-ROM. From this must be subtracted 166 sectors at the start of track 1 plus a few sectors for the file system, amounting to, say, 200 sectors leaving 336,100 sectors for user data.
- Mode 1 sectors contain 2048 bytes per sector giving a total capacity of 688,332,800 bytes or 656MB (where 1 MB = 1024 * 1024).
- Mode 2 sectors contain either 2048 or 2324 bytes per sector so will have a somewhat higher data capacity depending on the mix of the two types of sector.
The above assumes a CD-ROM comprising a single track in a single session. For multiple track/session discs the data capacity will be reduced.
Solution
With this information, now it is easy to develop a program to convert one image format to another.
The main routine in program is Convert. The code below, shows you the employed technique.
UINT Convert(LPVOID pParam)
{
PThreadData pth=(PThreadData) pParam;
int seek_header, seek_ecc, sector_size;
long i, source_length;
char buf[2352];
const BYTE SYNC_HEADER[12] =
{0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0};
FILE *fpSource, *fpTarget;
fpSource = _tfopen(pth->Source, _T("rb"));
fpTarget = _tfopen(pth->Target, _T("wb"));
if ((fpSource==NULL) || (fpTarget==NULL))
{
::SendMessage(pth->hwnd, WM_THREAD_TERMINATE, 0,
(LPARAM) FILE_FAILED);
return -1;
}
fread(buf, sizeof(char), 16, fpSource);
if (memcmp(SYNC_HEADER, buf, 12))
{
seek_header = 8;
seek_ecc = 280;
sector_size = 2336;
}
else
{
switch(buf[15])
{
case 2:
{
seek_header = 24;
seek_ecc = 280;
sector_size = 2352;
break;
}
case 1:
{
seek_header = 16;
seek_ecc = 288;
sector_size = 2352;
break;
}
default:
{
::SendMessage(pth->hwnd, WM_THREAD_TERMINATE,
0, (LPARAM) TRACK_UNSUPPORTED);
fclose(fpTarget);
fclose(fpSource);
return -1;
}
}
}
fseek(fpSource, 0L, SEEK_END);
source_length = ftell(fpSource)/sector_size;
fseek(fpSource, 0L, SEEK_SET);
for(i=0; i<source_length; i++)
{
fseek(fpSource, seek_header, SEEK_CUR);
fread(buf, sizeof(char), 2048, fpSource);
fwrite(buf, sizeof(char), 2048, fpTarget);
fseek(fpSource, seek_ecc, SEEK_CUR);
::SendMessage(pth->hwnd, WM_THREAD_PROGRESS, 0,
(LPARAM) ((i+1)*100/source_length));
}
fclose(fpTarget);
fclose(fpSource);
return 0;
}
This function called as a new thread when Convert button pressed.
Further Information
For further information refer to the Distronics web site. They have very useful information about various CD/DVD technologies on their web site.
Enjoy!
