13gb+ hard disk on a Pentium 75Mhz system?

By Rick ยท 10 replies
Apr 12, 2002
  1. If I'm not mistake, this P75 system I'm playing with is not going to recognize at the very most, an 8gb drive (Maybe even less like 4gb or 2gb?).

    I was thinking if I partitioned the drive in 8gb partitions (or a size it can handle), then it might be able to read it? But it seems to me that is more on the software level and not the hardware level.

    What can I do to get around this?
  2. Phantasm66

    Phantasm66 TS Rookie Posts: 5,734   +8

    I believe its more an issue of the hard drive geometry that the BIOS can address.... Partitioning it into 8 GB chucks won't help because its not the volume size that's the problem (that's more down to the file system and the operating system) its the actual physical or logically translated layout of the drive itself which is too much for the BIOS.

    You could try a BIOS upgrade to fix this, or purchase a seperate PCI IDE controller card which will have its own BIOS.
  3. Mictlantecuhtli

    Mictlantecuhtli TS Evangelist Posts: 4,345   +11

    Yes, I think that too. It's usually 1024th cylinder mark - which has not much to do with hdd's capacity - the limit was 512MB once, then 4GB, now usually about 8.3GB.
    If the BIOS only supports CHS addressing, you'll end up with the following limits:

    16 bits for the cylinder number (C), max. range 0..65535
    4 bits for the head number (H), max. range 0..15
    8 bits for the sector number (S), max. range 1..255

    This gives a maximum addressable sector range in CHS mode of 267386880 sectors (127.5GiB) but the spec allows this to be limited to (16383/16/63) or 16514064 sectors (7.8GiB). Most devices don't support CHS addressing beyond this limit.
  4. Phantasm66

    Phantasm66 TS Rookie Posts: 5,734   +8

    I could be wrong here but I believe that some operating systems (like Solaris and FreeBSD) can use their own means of addressing hard drive geometry, so that it does not matter what the BIOS thinks the hard drive geometry is. The OS implements is own... Whether or not this means you could actually install an OS like this on your P75 and use all of the hard drive's capacity I don't know but I seriously doubt it.

    In any case, essentially you have a BIOS that can't understand the layout of a hard drive that is beyond approx 8 GB in size, and if you try to use hard drive autodetection it will come up with an incorrect answer that is likely to be under 1 GB in size. You could of couse use this value if you liked, but you would be far better trying to find an 8GB HDD and using that....

    ....Or trying a BIOS upgrade or purchasing an IDE controller card as I mentioned. IDE Controller cards are not expensive and would provide a fix for your problem I believe.

    Other than that, I think you are stuck.
  5. Phantasm66

    Phantasm66 TS Rookie Posts: 5,734   +8

    Here this explains it all:


    So, to recap:

    1)Try a BIOS upgrade (Could be lucky....)

    2)Buy a seperate PCI IDE Controller card (Should definately work, provided the motherboard has a PCI bus...)

    3)Try a software tool. (Availability will depend on hard drive manufacturer and model....)
  6. Rick

    Rick TechSpot Staff Topic Starter Posts: 4,572   +65

    Thanks for the replies.

    I think the controller card might not be quite a good answer, since there is no PCI bus. I've never seen a disk controller designed for an ISA slot.

    Updating the BIOS is unlikely as well, since it is sooooo ooooold. The lastest BIOS update probably didn't even forsee 4gb let alone 8gb.

    I might try that software though. My question is.. How do you suppose it works?
  7. Rick

    Rick TechSpot Staff Topic Starter Posts: 4,572   +65

    Oh, by the way.. Excellent replies guys!

    When it comes to hard disks, I don't know enough on the techincal level. I think I need to read up some.
  8. Phantasm66

    Phantasm66 TS Rookie Posts: 5,734   +8

    You get controllers with the ISA design, or more accurately I should say got. If you manage to find one of these in this day and age I would be surprised. Essentially you are talking about a components that was designed for a motherboard where the IDE controllers were not part of the chipset. That's old. And anything like that probably has a BIOS with the 8 GB problem of its own anyway!

    As to the software, I imagine that this works like this:

    You let the BIOS detect whatever the hell geometry it likes and who cares.....

    You install the software by booting from a floppy and then running setup. You probably have to format the partition first or use the software's own partitioning and formatting tools.

    The software likely writes some code into the Master Boot Record and also makes some files (drivers and suchlike) on the partition itself, that tells the computer to cheat and ignore the BIOS's detected geometry and do something else.

    I am guessing about this but this would all make sense.

    What size of hard drive do you need???? I might be able to send you an older hard drive but I could not guarentee what state it would be in when it arrives....
  9. Rick

    Rick TechSpot Staff Topic Starter Posts: 4,572   +65

    I'm going to try some software to fix it. If that doesn't work, I suppose I'll have to resort to buying small drives.

    It supports 1gb drives at least... So I think it is beyond the 528mb limit era. This may make it possible to buy a couple >8gb drives.
  10. Mictlantecuhtli

    Mictlantecuhtli TS Evangelist Posts: 4,345   +11

    Ontrack's Disk Manager supports up to 8 GB drives. I have an old ISA IDE controller, and when I connect hdds to it instead of motherboard itself, they still show up the same way in motherboard's BIOS. So, I wouldn't count on them being a solution.
  11. Phantasm66

    Phantasm66 TS Rookie Posts: 5,734   +8

    The controller card would only be a solution if he had a PCI bus and could buy a brand new PCI IDE Controller card which would not have the 8 GB problem....

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