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> DOS > why when i boot from... |
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edfed 14 Jan 2011, 16:07
i have the same problem on my aspire one, when it boots on usb, it don't see anything else than A: and B: as the same usb pen.
even other usb drives are not recognised, ssd is absent, and SDcard too. but bios shows them in the boot devices. i think it is due to the bloatness of the modern PC world, they add features over features, instead of restating from scratch. it is the reason why manufacturers can sold hw so cheap, and build new versions so fast. it is elementary economy, applied to boot process.  |
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14 Jan 2011, 16:07 |
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Dex4u 14 Jan 2011, 19:26
Its very simple, to boot from cd you emulate a floppy or hdd, so all int 13h for floppy are pass to the floppy image on cd.
To make a cd bootable you useally need to use a floppy img and that where the apps are. You may beable to see them with winimage ? |
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14 Jan 2011, 19:26 |
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b1528932 14 Jan 2011, 20:01
i dont get it. Why i emulate? Isnt hd and cd on same bus? Meaning its working in same manner? CD have bootsector, there is no real diffrence between cd and hdd and floppy
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14 Jan 2011, 20:01 |
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Mike Gonta 14 Jan 2011, 22:01
b1528932 wrote: i dont get it. Why i emulate? Isnt hd and cd on same bus? Meaning its working in same manner? CD have bootsector, there is no real diffrence between cd and hdd and floppy “El Torito” Bootable CD-ROM Format Specification |
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14 Jan 2011, 22:01 |
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edfed 14 Jan 2011, 22:04
hem...
and for normal CDs like good old audio cd? how does it work? is there a boot sector? something like this? because, if you look well, CD ROM is a SCSI device, using IDE port on a PATA ribbon cable, with a compatibility to audio CDs, then, i doubt about the floppy emulation... because if you look well, you see that a CD rom is in fact a hard disk, with some lba adressing, N bytes per sectors, N sectors. for a total of 700MB, or 74 minutes of a symphony, readable even on a very basic CD player. it is that strange thing that lead to confusion i think. |
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14 Jan 2011, 22:04 |
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Mike Gonta 14 Jan 2011, 22:07
b1528932 wrote:
'El Torito' Bootable CD-ROM Format Specification wrote: If the CD-ROM boots as the A drive the systems normal A drive will become the B drive. If the system has a |
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14 Jan 2011, 22:07 |
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me239 14 Jan 2011, 23:30
This may sound stupid, but wouldn't a CD-R not be changeable no matter what the circumstances. If that's case.
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14 Jan 2011, 23:30 |
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b1528932 15 Jan 2011, 08:29
Ok, b is actually there. But i bet i checked agnist this scenario before posting...
Quote: and for normal CDs like good old audio cd? isnt there? cd/dvd sector is something 23XX bytes large, and i can use either all of bytes for data, or reserve space for error correction data. When mounting audio cd i will just have information about tracks where data is stored, no filesystem. And i do have a question wich been bothering me for some time. using bios int 13 i can read data from drive. How does actual data transfer is managed? Can i transfer 'at once' no less than 1 sector? Is the sector some sort of atom in nonvolatile media? Quote: CD ROM is a SCSI device, using IDE port on a PATA ribbon cable what? it doesnt make sense to me. Could you be more precise? For me, scsi and pata are just cable types and interfaces used to transmit data. And now your telling me that 'scsi' is a generic device... wtf! |
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15 Jan 2011, 08:29 |
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ManOfSteel 15 Jan 2011, 14:01
b1528932 wrote: Can i transfer 'at once' no less than 1 sector? If you poll the disk using the in instruction, probably. But using the BIOS's int 0x13? No, I don't think so. b1528932 wrote:
ATAPI devices speak SCSI on a command/response-level. In the beginning, there were only SCSI CD-ROM devices, which were very expensive. So they started to make ATA CD-ROM devices. They practically emulated SCSI devices and just gave them ATA interfaces and cabling. |
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15 Jan 2011, 14:01 |
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b1528932 15 Jan 2011, 18:15
So scsi is not just cable, its also a language.
Is it true, that even usb device might speak scsi so OS will show it as a cdrom or something else? |
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15 Jan 2011, 18:15 |
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ManOfSteel 15 Jan 2011, 19:52
b1528932 wrote: So scsi is not just cable, its also a language. It's not a language. It's an interface. And like all interfaces it has commands that make an interaction possible. Just like ATA has its own commands. b1528932 wrote: Is it true, that even usb device might speak scsi so OS will show it as a cdrom or something else? The computer (BIOS) itself can see it as different possible devices. For example, if I were to enter my machine's BIOS boot devices settings, I would see the USB pendrive I just inserted listed as an internal disk right under my 2 real internal disks. |
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15 Jan 2011, 19:52 |
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