🚀 go-pugleaf

Mike Clarke <mike@helix.demon.co.uk> wrote:

>Several weeks ago in article <610520714wnr@naismith.demon.co.uk>, John
>Naismith <John@naismith.demon.co.uk> writes:

>>The capabilities of DOS are constrained by a combination of the IDE spec & the 
>>BIOS. The IDE spec allows for hard disk sizes of up to 130GB, whilst a 
>>"standard" (non-LBA) PC BIOS can handle disks of up to 8GB in size. The 504MB 
>>"limit" occurs because of a mismatch between the drive geometries supported by 
>>each hardware standard. The problem is that DOS uses the "lowest common 
>>denominator". ie -
>>
>>                       BIOS       IDE      DOS
>>Max sectors/track       63        255       63
>>Max Heads              255         16       16
>>Max Cylinders          1024      65536    1024
>>
>>To calculate sizes from Sectors, etc, use the following formula :
>>
>>sectors x heads x cylinders x 512 = capacity in *bytes*. To convert to MB divide 
>>your answer by 1,048,576. 
>>
>>This gives : BIOS limit = 8,032.5MB; IDE limit = 130,560MB; DOS limit = 504MB

>Thanks John for a very informative article which I duly archived for
>future reference. The future has now arrived since I am considering
>adding a 1.2Gb disk to my system, after dusting down and re-reading the
>article I find that my system does not quite match the above figures and
>am still a little uncertain as to whether or not I will will suffer from
>the 504Mb limit.

>My PC has an old (9/6/92) AMI BIOS so I initially assumed that I would
>need either an EIDE card or something like Ontrack, but when I fiddle
>about with the BIOS setup I find that it will let me specify up to 255
>sectors/track instead of the expected 63. If I specify 255
>sectors/track, 255 heads and 1024 cylinders the BIOS returns a size of
>32,513MB. Combining these with the IDE limit suggests that my DOS limit
>would be 2040Mb.

>Considering the date of my BIOS I'm inclined to think the figures are
>wishful thinking but I'd like to be certain of my requirements before
>ordering the goods.

>Has anybody had experience, favourable or otherwise, of using large
>disks with the June 1992 AMI BIOS?

>-- 
>Mike Clarke



You will need software such as On track to get passed the 504Mb limit.
So check with your supplier that you will get a copy of the correct
software for the drive (different drives, different software) before
ordering. If not use a supplier that will supply it.
*************************************
Colin Muirhead
E-mail:- colin@buzzcomp.demon.co.uk