Re: MSDOS before cyl 1024

From	"Carlos E.R." <robin_listas@es.invalid>
Newsgroups	comp.os.linux.misc
Subject	Re: MSDOS before cyl 1024
Date	2023-01-21 21:16 +0100
Message-ID	<3ptt9jxasi.ln2@Telcontar.valinor> (permalink)
References	(3 earlier) <tqgq6a$2k44c$2@dont-email.me> <ea7t9jx7k1.ln2@Telcontar.valinor> <tqh3jv$2l37n$4@dont-email.me> <p6rt9jxg6f.ln2@Telcontar.valinor> <tqhfll$2lj4a$3@dont-email.me>

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On 2023-01-21 20:50, Lew Pitcher wrote:
> On Sat, 21 Jan 2023 20:32:09 +0100, Carlos E.R. wrote:
>> On 2023-01-21 17:24, Marco Moock wrote:
>>> Am 21.01.2023 um 14:52:46 Uhr schrieb Carlos E.R.:
>>>
>>>> Today they only specify the LBA sector.
>>>
>>> Can old disks (non-LBA) still be used with them?
>>
>> That's a good question.
>>
>> I suspect that disks or BIOS had both for years.
>>
>> However, on MsDOS times common disks had the parallel cable or interface
>> (PATA) while now they all use SATA.
>>
>> I don't remember all the details :-)
>>
>> There was an even older interface, used by disks with stepper motors on
>> the head arm. That's what the IBM PC and compats used.
> 
> Before the advent of a BIOS that recognized Logical Block Addressing ("LBA"),
> the BIOS used Cylinder/Head/Sector ("CHS") addressing. There was a limit to this
> addressing scheme that meant that it could not access more than 1024
> cylinders.
> 
> For MSDOS to boot, it's partition needed to be marked "bootable", and be
> located within this 1024 cylinder limit, as the BIOS could not reach
> a boot partition outside of this limit. Thus, the rule of thumb that
> the bootable partition /must/ reside within the first 1024 cylinders
> of the disk.
> 
> However, when the BIOS implementations (and probably, disk controllers)
> moved to LBA, this limit effectively disappeared, as now the bootable
> partition had a 32bit disk address space to live in.

Reminds me. Linux could use bigger disks, but LILO could not, because it 
used BIOS services to run and load the kernel initially. The trick then 
was to create first a small /boot partition for LILO to live in, and the 
kernel. Then the rest of the system could be beyond that cylinder, 
because the kernel could access it.

So sometimes we had to reduce the size of the partition holding dos or 
windows to make for "/boot" (maybe 100 MB was enough), and then the 
system could be at the end of the disk.

-- 
Cheers, Carlos.

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Thread

MSDOS before cyl 1024 vjp2.at@at.BioStrategist.dot.dot.com - 2023-01-20 15:10 +0000
  Re: MSDOS before cyl 1024 Marco Moock <mo01@posteo.de> - 2023-01-20 19:04 +0100
  Re: MSDOS before cyl 1024 Vilmos Soti <vilmos@soti.ca> - 2023-01-21 03:00 -0800
    Re: MSDOS before cyl 1024 Marco Moock <mo01@posteo.de> - 2023-01-21 13:23 +0100
      Re: MSDOS before cyl 1024 The Natural Philosopher <tnp@invalid.invalid> - 2023-01-21 13:43 +0000
        Re: MSDOS before cyl 1024 "Carlos E.R." <robin_listas@es.invalid> - 2023-01-21 14:52 +0100
          Re: MSDOS before cyl 1024 Marco Moock <mo01@posteo.de> - 2023-01-21 17:24 +0100
            Re: MSDOS before cyl 1024 "Carlos E.R." <robin_listas@es.invalid> - 2023-01-21 20:32 +0100
              Re: MSDOS before cyl 1024 Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2023-01-21 19:50 +0000
                Re: MSDOS before cyl 1024 "Carlos E.R." <robin_listas@es.invalid> - 2023-01-21 21:16 +0100
                Re: MSDOS before cyl 1024 Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2023-01-21 20:45 +0000
                Re: MSDOS before cyl 1024 The Natural Philosopher <tnp@invalid.invalid> - 2023-01-22 09:39 +0000
              Re: MSDOS before cyl 1024 "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2023-01-21 15:53 -0500
                Re: MSDOS before cyl 1024 "Carlos E.R." <robin_listas@es.invalid> - 2023-01-22 04:47 +0100
              Re: MSDOS before cyl 1024 The Natural Philosopher <tnp@invalid.invalid> - 2023-01-22 09:35 +0000
                Re: MSDOS before cyl 1024 "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2023-01-22 05:08 -0500
          Re: MSDOS before cyl 1024 Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2023-01-22 21:33 +1100
            Re: MSDOS before cyl 1024 "Carlos E.R." <robin_listas@es.invalid> - 2023-01-22 14:29 +0100
  Re: MSDOS before cyl 1024 vjp2.at@at.BioStrategist.dot.dot.com - 2023-01-22 20:13 +0000
    Re: MSDOS before cyl 1024 Marco Moock <mo01@posteo.de> - 2023-01-23 10:08 +0100
    Re: MSDOS before cyl 1024 Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2023-01-26 14:40 +1100

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