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From: Thomas Koenig <tkoenig@netcologne.de>
Newsgroups: comp.arch
Subject: Re: tiny COBOL, Article on new mainframe use
Date: Mon, 2 Sep 2024 09:16:42 -0000 (UTC)
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Terje Mathisen <terje.mathisen@tmsw.no> schrieb:
> Thomas Koenig wrote:
>> Stefan Monnier <monnier@iro.umontreal.ca> schrieb:
>>>> A C64 had 64K 8-bit bytes of RAM,
>>>
>>> Indeed (tho, IIRC 8kB of those were hidden by the ROM, tho you could
>>> change the mapping to hide different 8kB at different time and thus
>>> access the full 64kB of RAM).
>> 
>> For doing highly useful things like changing the name of the BASIC
>> commands:  It was possible to PEEK from the ROM and POKE to
>> the underlying RAM.
>> 
>>>
>>>> and the floppies held about 1.2MB but they were a
>>>> whole lot cheaper than 1311 disk packs.
>>>
>>> IIRC they held only ~170kB.
>> 
>> And were extremely slow - around 300 bytes per second, comparable
>> to a card reader.  But fast loaders could improve on that up to 10 kB/s.
>
> They did that by reading every 1/2 sector, then reassembling after 2 
> rotations, instead of having to wait a full rotation between every 
> sector read?

Just reading up on this... it seems that there was a bug in the
6522 I/O controller where the shift register sometimes dropped
a bit due to a race condition, and the workaround which was
hastily put in place was very slow.