Hi,
Ofcourse there is a huge performance loss instead of just copying
the data to its final destination, which probably is just on step.
You have to read and write all data a second time to be able
to store it in the cache.
The problem with the storage is that you also have to select the
most ideal situation to be able to execute a simple LDIR to copy
the data. And maybe some extra slotswitches and memory mapper
switches through the proper channels if your working with DOS2.
If there should be something that a caching mechanism should
eliminate then it would be the seek times of a harddisk, that is
if the seek times are a problem.
How about optimizing the caching of the FAT and directory structures.
Frits
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf
> Of Laurens
> Holst
> Sent: Thursday, June 29, 2000 3:30 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Out to #FC-#FF
>
>
> > >Cache makes your drive much slower. My Sunrise IDE:
> > >w/o cache: 230 kbps
> > >w/ cache: 50 kbps
> >
> > How did you test this? By just testing disk I/O time?
>
> Yes. And you should have quoted (or at least read) the rest
> of my message
> too.
>
>
> > Well then you probably
> > don't understand caching: (I can hardly believe it, me
> explaining you
> > something :-) )
>
> I already know how cache works. Otherwise I wouldn't use it, don't you
> think?
>
>
> > present in the cache - is needed again, cache is just a
> waste of time.
> > Cache doesn't make I/O faster, but reduces the times the
> slowest I/O is
> > needed. So in practice you will gain speed.
> > How larger the memory used for cache, how higher the chance
> used data is
> > present in the cache, so how faster disk acces becomes.
>
> I know, but as I said the gain in speed reading cached data
> is very small
> compared to when using non-cached data only. And the loss in
> speed when
> reading non-cached data is huge.
>
> Let me explain you something about how the Sunrise
> IDE-interface works (and
> I think the MegaSCSI also works this way). The interface uses a
> memory-mapped I/O system, hence it doesn't use any I/O ports,
> but memory
> addresses instead. It is designed in a very smart way,
> because the sector
> read from the drive is DIRECTLY loaded into a dedicated area of the
> IDE-interface its memory. The only thing which has to be done
> is using an
> LDIR to move it to the appropriate location.
>
> When caching the data (first time scenario), an additional
> LDIR is issued to
> move it to the cache-memory, so that makes 2 LDIR's per
> sector read, instead
> of one without cache. When reading cached data, it is LDIRed from the
> cache-memory, but when reading from disk also only one LDIR
> is used, so in
> that case there is no gain either (but also no loss). In
> theory there still
> is a small gain in the last scenario, because the cache can
> LDIR the cached
> data in larger chunks, and it doesn't have to wait for the
> harddisk (however
> you won't really notice it on MSX with new harddisks). But in
> practice, this
> gain is very little and absolutely NOT worth 50% of my 2MB
> mapper and the
> slow first-time loading.
>
> On my old BERT (I/O-based) SCSI-interface, the non-cached
> transfer rate was
> about 50kb/s. So on that one, caching really did make a difference.
>
>
> ~Grauw
>
>
> --
> >>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<
> email me: [EMAIL PROTECTED] or ICQ: 10196372
> visit my homepage at http://grauw.blehq.org/
> >>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<
>
>
> ****
> MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED]
> and put "unsubscribe msx [EMAIL PROTECTED]" (without the quotes) in
> the body (not the subject) of the message.
> Problems? contact [EMAIL PROTECTED]
> More information on MSX can be found in the following places:
> The MSX faq: http://www.faq.msxnet.org/
> The MSX newsgroup: comp.sys.msx
> The MSX IRC channel: #MSX on Undernet
> ****
****
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED]
and put "unsubscribe msx [EMAIL PROTECTED]" (without the quotes) in
the body (not the subject) of the message.
Problems? contact [EMAIL PROTECTED]
More information on MSX can be found in the following places:
The MSX faq: http://www.faq.msxnet.org/
The MSX newsgroup: comp.sys.msx
The MSX IRC channel: #MSX on Undernet
****
