DOS ain't dead

On what filesystem? FreeDOS natively supports only FAT32 so 2TB limit. Of course you can write your own low-level code to R/W entire disk...

---
DOS gives me freedom to unlimited HW access.

> Can FreeDos handle 16 TeraByte disks ?

Depends on the definition of "handle". As mentioned earlier in this thread, the BIOS will support this if it has LBA48. You do not need 64-bit registers, because you pass a data structure in RAM to the BIOS which contains a 64-bit sector number of which you can use the low 48 bit if the BIOS supports LBA48. See RBIL about int 0x13 functions 0x42 and 0x43. For 16 terabyte, even with 512 byte per sector, you only need 35 bits for the sector numbers.

> Can I write 64 Bit Register Instructions to run under FreeDos ?

You can use FPU registers which can be 64, 80, 128... I have lost track of all those weird extensions for parallel computation on floating point units of modern processors. You probably can NOT use 64 Bit main CPU integer registers in plain DOS. For that, you need to run in a task which is in 64 Bit Long Mode. But some bold DOS programmers are working on DOS extenders for Long Mode if you want to give it a try. This also lets you use more than 4 GB RAM without having to switch between different areas and without having to copy stuff around into buffers in the first 4 GB etc.

> I want to write some stuff that will allow me to access specific disk
> sectors.

You can do that easily with the help of the BIOS.

> In my case I want to verify that the sectors actually exist.

Sounds easy enough. Also read int 0x13, function 0x48 and similar to get info about how large your disk claims to be.

Note that FreeDOS does not yet understand GUID partition tables, nor sectors larger than 512 bytes, so you cannot partition disks above 2 TB in a way which FreeDOS would understand. But for example USB disk drivers can handle the partitioning themselves to free DOS from having to understand it

In your specific example, you do not seem to need any understanding of partition tables anyway, as you plan to only access raw sectors.

Note that writing 16 TB of data to a disk just to see whether you can write it will take very long. Also, if anything goes wrong, you will have invented a disk wiper instead of a disk tester.

---
FreeDOS / DOSEMU2 / ...

> Can FreeDos handle 16 TeraByte disks ?
no. FreeDOS (as of now) is limited to a 2 TB MBR partitioning scheme.

although
> Can I write 64 Bit Register Instructions to run under FreeDos ?

absolutely yes. FreeDOS doesn't interfere with that. AT ALL.

it only communicates with disks via INT13, and doesn't care at all about register level access.

> Can FreeDos handle 16 TeraByte disks ?
>
> Can I write 64 Bit Register Instructions to run under FreeDos ?
>
> I want to write some stuff that will allow me to access specific disk
> sectors.
>
> In my case I want to verify that the sectors actually exist.
>
> e.g.,
>
> - Read "N" bytes of data at disk sector XYZ
> - Write a different string of "N" bytes back onto sector XYZ
> - Read that same data from that same sector back into a different buffer
> - Compare the two
> - If good, put the original data back into its place
> - (Else, If Bad, worry about that later)
> - Repeat this process for higher and higher disk sectors

IMO, doing all of that with a DOS program while booted to FreeDos
would be pretty-much the same as this little 'experiment'
of a mine a few months ago.

Namely.... not for any actual useful purpose
but rather simply to prove it could be done.

https://www.linuxquestions.org/questions/slackware-14/just-to-prove-it-*could*-be-done-4175709646/

---
--
http://glennmcc.org/

Hello CLINT,

> Can FreeDos handle 16 TeraByte disks ?
>
> Can I write 64 Bit Register Instructions to run under FreeDos ?

As mentioned, you can work with 64-bit sector numbers without having to use 64-bit CPU registers (or even a 64-bit CPU).

You can quite easily do basic 64-bit arithmetic with 32-bit — or even 16-bit — CPU registers.

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

Hello CLINT,

Also, it is probably a bad idea to write stuff to a hard disk just to "probe" for things. If the power on your PC goes out in the middle of a write, then you end up with a corrupted hard disk with no easy way to undo the corruption.

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"