Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: QUESTION: Are IDE cacheing controllers better than Smartdrive?
From: eputnam@vax1.umkc.edu
Date: Thu, 8 Oct 1992 00:08:42 GMT
Organization: University of Missouri - Kansas City

In article <91932@netnews.upenn.edu>, sergei@upenn5.hep.upenn.edu (Sergei Borodin) writes:
> In article <Bvpytn.Boo@ais.org> miax@ais.org (Kris Kortright) writes:
> 
>>      Im wondering, are those IDE cacheing controllers, the ones that can
>>make your access time like 0.03 ms as opposed to 15 for my harddrive, and
>>can have 8 megs on them, that are a 16 bit card better than programs like
>>smartdrive or Qcache for speeding up harddrive loading?  The cards sound
>>great, but someone said they thought the program ones were just as good, is
>>this true?
> 
>   It cannot be true. All that program does is that it loads more sectors 
>  into memory than have been requested.  During "writes" it suspends disk
>  access until the buffer is filled up. Note that all this things are, in
>  fact, done partially bu uP. Partially  - because 'smart drive' trys to 

[several very true statements deleted]

> 
>  The main difference is that cacheing controller doesn't allocate
>  memory in a processor address space and (till certain extent) needs
>  no processor to be involved, when
>   'smartdrive' requires additional processor intervention, which
>  is very time consuming.
> 

Very good arguments against software caching, but there is still one overriding
weakness to hardware caching... it all still has to go through the bus.  Soft-
ware caches are in memory, thus the "transfers" are done at memory speeds not
bus rates.  For us ISA users that is a BIG difference.  True, when the actual
movement of data occurs you will lose with the software cache, and you do have
to dedicate more CPU cycles to software caches, but for the cost of SIMMs, you
can get a software cache AND have more memory for those really big apps which
are on their way if you need it.  Personally, I have a Promise Tech DC-2032
IDE caching controller with 8 Meg of memory on it.  It gave me a tremendous
boost in performance under OS/2 because I was able to free memory from the
software cache AND reduce CPU loading since the controller was able to manage
continous reads on its own while the CPU switched tasks.  However, adding 8
Meg of physical RAM would probably have given better improvements just because
the system would not be swapping so much to the drive in the first place.
For those of you wondering why I didn't add more mem, there is no space left
on my motherboard (8 1Meg SIMMs).

In my opinion, the only time to use a caching controller is when you've filled
all of the memory slots on your motherboard.  Until that happens, your spending
money on memory which is available only to one specific task.  And if
you are looking for a good caching controller, the Promise Tech line is one 
of the best on a dollar per dollar basis (IMHO).  The total cost for me to
get the controller and 8 Meg of memory was $480.  The card I chose even had
2S and 1P port so that it perfectly replaced my old IDE card (you just plug it
in and go!; no drivers or reformating necessary!).

Newsgroups: comp.sys.ibm.pc.hardware