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The 640 Meg Shareware Studio CD-ROM Volume II (Data Express)(1993).ISO
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1992-07-16
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4KB
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TIP #: 020
KEYWORDS: DESQview, Caching, Super PC-Kwik
UPDATED: September, 1990
PROBLEM: How should caching be set up under DESQview? Is it different than
under DOS?
SYMPTOMS: Improper caching setup under DESQview can introduce many unwanted
side-effects. These include slow operation, file corruption, and
hangs.
SOLUTION: The most important thing is to choose the right caching program.
My recommendation would be Super PC-Kwik. From my own experience,
this is the fastest and most compatible of the caches. I have also
used ADCACHE and PC-Cache 5.5 with success. I have not been able
to get PC-Cache 6.0 to work reliably. At this point, I would not
recommend PC-Cache 6.0.
A cache works by buffering information read from the hard disk into
memory. Then when a read request comes along, the memory is
checked for the information. If it is in memory already, the
information is transferred without any hard drive activity! Since
memory is much faster than any hard drive, the system operates
faster. Some of the newer caches such as Super PC-Kwik, ADCACHE,
and PC-Cache 6.0 also offer a feature called "Write-Caching". This
allows the cache to buffer disk writes as well as disk reads.
Under DESQview, this feature should be turned off. Otherwise
DESQview could terminate an application without the cache being
flushed first. If your machine ever hangs, you may suffer file
corruption. Always load the cache before DESQview.
I also recommend running your cache under Expanded (EMS) memory.
Although EMS is slightly slower than Extended, there are less
problems with interrupt latency when running in EMS. If you are
doing any communications from within DESQview, use EMS, not
extended.
My parameter line to invoke Super PC-Kwik is as follows:
SUPERPCK /A+ /S:3000 /H- /D- /T:8 /P- /-A /-B /-M /-N
This sets up Super PC-Kwik to: use expanded memory (/A+), 3
megabytes (/S:3000), disable write caching on the hard drive (/H-),
disable write caching on the floppy drives (/D-), buffer 8 sectors
(/T:8), don't display the parameters at bootup (/P-), don't buffer
floppy A: or B: (/-A /-B), and don't buffer the RAM drive or CD-ROM
(/-M /-N).
The /T:8 parameter may need a little more explanation. When an
application requests a disk read, most caches allow you to specify
how much of the rest of the track to read in to the buffer. Super
PC-Kwik defaults to reading the entire track (/T+). Normally this
is okay, but in my case I have an ESDI drive which claims to have
63 sectors per track. When an application requested a disk read on
my system, the cache would read in the rest of the track, up to 63
sectors! This actually caused a reduction in the effectiveness of
the cache. On MFM drives with 17 sectors per track, you may be
able to use the defaults, but on RLL or ESDI drives, you are better
off reducing the number of sectors to read in. You can experiment
with different settings by using the parameters option and trying
different settings. With enough memory and the proper settings it
is possible to get "hit rates" greater than 90%. My system
typically runs about 93% or more.
Although I have detailed the settings for Super PC-Kwik, the
concepts are similar no matter what cache you use.
Another often overlooked benefit of caching is that you can reduce
the number of DOS buffers needed. Usually you can set BUFFERS=4 or
BUFFERS=6 in your CONFIG.SYS. This helps to regain some of the
memory lost by the cache program itself. You can usually load the
cache into high RAM if you have enough room. I have successfully
loaded Super PC-Kwik, ADCACHE, and PC-Cache 5.5 high.