Re: 32MB is size???

[pausch@saaf.se (Paul Schlyter)]

In article <HKeYf.44493$_S7.34984@newssvr14.news.prodigy.com>,
Bryan Parkoff <none@nospam.net> wrote:

> "Paul Schlyter" <pausch@saaf.se> wrote in message 
> news:e0pfuc$2s0u$1@merope.saaf.se...
>> In article <vTVXf.7800$4L1.2405@newssvr11.news.prodigy.com>,
>> Bryan Parkoff <none@nospam.net> wrote:
>>> "Paul Schlyter" <pausch@saaf.se> wrote in message
>>> news:e0oh20$2h45$1@merope.saaf.se...
>>>> In article <iAHXf.51135$2O6.5759@newssvr12.news.prodigy.com>,
>>>> Bryan Parkoff <none@nospam.net> wrote:
>>>>
>>>>> Hi, I suggest you to read "Beneath to ProDOS" and "Beneath to DOS 3.3"
>>>>> manual.  DOS 3.3 is designed to read 256 bytes per sector at this time.
>>>>> ProDOS is designed to read 512 bytes per two sectors at this time.  It
>>>>> shows that ProDOS is faster than DOS 3.3 for reading and writing 
>>>>> because
>>>>> double sectors are stored in the RAM.
>>>>
>>>> No, that's not the reason ProDos reads so much faster than DOS 3.3.
>>>>
>>>> One can fairly easily patch DOS 3.3 so it reads about as fast as
>>>> ProDos does.  A number of special DOS'es, with these patches, are
>>>> known by names like Diversi-Dos, Pronto-Dos, etc --- all of them use
>>>> 256-byte sectors, both at the sector level as well as at the OS level.
>>>>
>>>> -- 
>>>> ----------------------------------------------------------------
>>>> Paul Schlyter,  Grev Turegatan 40,  SE-114 38 Stockholm,  SWEDEN
>>>> e-mail:  pausch at stockholm dot bostream dot se
>>>> WWW:     http://stjarnhimlen.se/
>>>
>>> Paul,
>>>
>>> Well, unpatched DOS 3.3 executes 6502 instructions by using extra cycles
>>> because of crossing page boundary.  ProDOS borrowed patched DOS 3.3 to
>>> reduce cycles by increasing performance so crossing page boundary is
>>> avoided.
>>>
>>> Bryan Parkoff
>>
>> I never denied that.  But you claimed that this page boundary stuff was
>> the reason unpatched DOS 3.3 reads disk so much slower than ProDos.  And
>> that's what I objected to.
>>
>> The reason unpatched DOS 3.3 is so slow is that it pipes all its disk
>> I/O stuff through a "read one byte" (and, if writing, "write one byte")
>> subroutine.  And that subroutine saves and restores an environment 45 
>> bytes
>> large each time it is called.  This means that if you read (or write) a 
>> large
>> number of bytes, those 45 bytes are needlessly swapped back and forth for
>> each and every byte read.  This slows down unpatched DOS 3.3 enough to
>> make it miss the next sector when it passes under the disk r/w head, 
>> forcing
>> DOS 3.3 to wait another disk revolution for the next sector.
>>
>> Compared to this "swap 45 bytes back and forth for each and every byte 
>> read",
>> the delay due to the page boundary stuff you mention is quite 
>> insignificant.
>>
>> -- 
>> ----------------------------------------------------------------
>> Paul Schlyter,  Grev Turegatan 40,  SE-114 38 Stockholm,  SWEDEN
>> e-mail:  pausch at stockholm dot bostream dot se
>> WWW:     http://stjarnhimlen.se/
> Paul,
> 
>     Well, I can't remember the article when patched DOS 3.3 and ProDOS had 
> some ways to reduce approximately 10,000 cycles which it runs faster.
> 
> Bryan Parkoff