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Re:Why do PCs load their boot sector at 7C000h linear? by userbinator on Saturday September 26, 2015 @09:18AM (#10283020)
I feel old for recognising that address and knowing the answer to the question before I even read the article...

You can see the actual bootloader code in the PC's BIOS here:

http://static.pcjs.org/pubs/pc/reference/ibm/5150/techref/19...

The address is mentioned in lines 44 and 45 here:

http://static.pcjs.org/pubs/pc/reference/ibm/5150/techref/19...

(It would be so very awesome if this was the sort of documentation you got if you purchased a new computer, although perhaps on a disc instead of hardcopy.)

[ Parent | on HN ]
Re:Why do PCs load their boot sector at 7C000h linear? by 2sk21 on Saturday September 26, 2015 @06:14AM (#10282681)
I love this kind of software archeology. I think I first came across this term in Vernor Vinge's book "A Deepness in the Sky".
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Re:Why do PCs load their boot sector at 7C000h linear? by pavedwalden on Saturday September 26, 2015 @02:20PM (#10283925)
I'm not sure which Zones Of Thought book it was (probably Deepness in the Sky), but my favorite software joke in SciFi is when someone deep-diving into the system discovers that at the deepest layers timekeeping is still calculated from the UNIX epoch on the long lost human homeworld.
[ Parent | on HN ]
Re:Why do PCs load their boot sector at 7C000h linear? by acheron on Saturday September 26, 2015 @03:56PM (#10284224)
Reminds me of this: http://abstrusegoose.com/323
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Re:Why do PCs load their boot sector at 7C000h linear? by madez on Saturday September 26, 2015 @04:00PM (#10284232)
I wouldn‘t call it software archeology because it is still very much in use and modern standard.
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Re:Why do PCs load their boot sector at 7C000h linear? by yuhong on Saturday September 26, 2015 @04:38AM (#10282565)
It is 7C00h linear.
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Re:Why do PCs load their boot sector at 7C000h linear? by raverbashing on Saturday September 26, 2015 @05:58AM (#10282664)
Yeah, it's not 7C00:0000, it's 007C:0000 (or 0000:7C00)

shudders

[ Parent | on HN ]
Re:Why do PCs load their boot sector at 7C000h linear? by wruza on Saturday September 26, 2015 @07:57AM (#10282843)
07C0:0, actually :)
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Re:Why do PCs load their boot sector at 7C000h linear? by raverbashing on Saturday September 26, 2015 @08:04AM (#10282857)
True, too bad I can't fix in the original comment

"The 16-bit segment selector in the segment register is interpreted as the most significant 16 bits of a linear 20-bit address"

However, Wikipedia has a funny quote on that

"Once the BIOS has found a bootable device it loads the boot sector to linear address 7C00h (usually segment:offset 0000h:7C00h, but some BIOSes erroneously use 07C0h:0000h"

https://en.wikipedia.org/wiki/Booting#BOOT-LOADER

[ Parent | on HN ]
Re:Why do PCs load their boot sector at 7C000h linear? by MatthewWilkes on Saturday September 26, 2015 @11:35AM (#10283346)
Can someone provide a TL;DR? I'm finding it very hard to understand the article.
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Re:Why do PCs load their boot sector at 7C000h linear? by Dylan16807 on Saturday September 26, 2015 @12:02PM (#10283421)
IBM's BIOS put the boot loader at the end of the minimum amount of memory at the time (32KB). 7C00-7DFF get the boot sector, and 7E00-7FFF are scratch space.

Also once upon a time SCP tucked it into 0200-03FF because that ram was otherwise unused.

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Re:Why do PCs load their boot sector at 7C000h linear? by yuhong on Saturday September 26, 2015 @02:18PM (#10283913)
the minimum was 16KB I think (they used 4116s).
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Re:Why do PCs load their boot sector at 7C000h linear? by Dylan16807 on Saturday September 26, 2015 @02:27PM (#10283948)
Well, I'm just summarizing.

> "DOS 1.0 required a minimum of 32KB, so we weren't concerned about attempting a boot in 16KB."

> (Note: DOS 1.0 required 16KiB minimum ? or 32KiB ? I couldn't find out which correct. But, at least, in 1981's early BIOS development, they supposed that 32KiB is DOS minimum requirements.)

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Re:Why do PCs load their boot sector at 7C000h linear? by yuhong on Saturday September 26, 2015 @02:29PM (#10283960)
There are different configs of IBM PC, the cheapest which relied on the ROM BASIC and cassette tape.
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Re:Why do PCs load their boot sector at 7C000h linear? by Dylan16807 on Saturday September 26, 2015 @02:30PM (#10283963)
Right, but we're worried here about the ones booting DOS, while they were designing this.
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Re:Why do PCs load their boot sector at 7C000h linear? by fogleman on Saturday September 26, 2015 @11:22AM (#10283314)
So it was the same guy who came up with Ctrl+Alt+Del.
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Re:Why do PCs load their boot sector at 7C000h linear? by Peaker on Saturday September 26, 2015 @10:45AM (#10283213)
Do you intentionally leave out parens in the #define for MODULE_SIZE?

If it was used in a context with higher precedence than multiplication, it'd be a bug.

[ Parent | on HN ]
Re:Why do PCs load their boot sector at 7C000h linear? by roghummal on Saturday September 26, 2015 @06:30AM (#10282700)
TerryADavis might have something meaningful to say here if given the chance. Can YC selectively un-auto-[dead] people?
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Re:Why do PCs load their boot sector at 7C000h linear? by eru on Saturday September 26, 2015 @07:49AM (#10282826)
Quoting his comment:

TerryADavis 2 hours ago [dead] http://www.templeos.org/Wb/Adam/Opt/Boot/BootMHD.html http://www.templeos.org/Wb/Adam/Opt/Boot/BootMHD2.html http://www.templeos.org/Wb/Adam/Opt/Boot/BootHD.html

---- [End of Quote]

Thanks, Terry!

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Re:Why do PCs load their boot sector at 7C000h linear? by buffoon on Saturday September 26, 2015 @12:38PM (#10283534)
And today I learn about Terry Davis, TempleOS and showdead. Moderation and censorship is a travesty online. Fortunately showdead allows us to bypass it somewhat.
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Re:Why do PCs load their boot sector at 7C000h linear? by eru on Monday September 28, 2015 @12:17AM (#10288893)
There's a distinction between going out and censoring people, and not letting them post anything they want on your domain.
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Re:Why do PCs load their boot sector at 7C000h linear? by buffoon on Monday September 28, 2015 @01:52AM (#10289099)
No there is not.
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Re:Why do PCs load their boot sector at 7C000h linear? by eru on Monday September 28, 2015 @04:02AM (#10289344)
I'll book a trip to your house and write on your walls, then.
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Re:Why do PCs load their boot sector at 7C000h linear? by buffoon on Tuesday September 29, 2015 @04:33AM (#10295174)
I have kids. I'm already there.
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Re:Why do PCs load their boot sector at 7C000h linear? by dang on Saturday September 26, 2015 @03:31PM (#10284149)
Soon the community will be able to selectively un-auto-[dead] comments. We've been working on this for a long time. It's currently in alpha testing, and indeed the alpha-testers (not moderators) unkilled https://news.ycombinator.com/item?id=10282575, which is precisely the intent of the feature.
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