🚀 go-pugleaf

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