From: hgg@ecs.soton.ac.uk (Harald Geiger)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: local bus hard disk
Date: 28 Jan 93 22:36:36 GMT

In <1993Jan24.014406.27423@mlb.semi.harris.com> sonny@charybdis.harris-atd.com (Bob Davis) writes:

>In article <1993Jan23.231824.24755@rose.com> gyl.midroni@rose.com (gyl midroni) writes:
>	[DELETIONS]
>>    It seems to me that local bus disk access will be a speed booster 
>>for the reason of faster data communicatio with the CPU / memory.  It 
>>is four times faster to get data off the disk at 33 MHz off the local 
>>bus connection to the CPU and memory than at 8 MHz via the ISA bus. 
>>As simple as that... no? 

>	Seems like the local bus might deliver 33 Mhz x 4 bytes delivered
>in parallel for 132 million bytes/sec, and the 8 MHz ISA 16-bit bus slot
>can deliver about 5.33 million bytes/sec (assuming 2 bytes delivered
>in parallel every 3 clock cycles). So the local bus could be about
>25 times faster than the ISA bus.

Agreed. The real numbers for the ISA bus are about 8MB/s, but that is
beside the point.

> That is great for rapidly stuffing huge 
>quantities of image information into electronic-quick video memory on a local 
>bus video card. It might not be so great for the mechanical-slow ( relatively
>speaking ) rotating machinery of a hard drive managed by a local bus disk
>controller. 
>	Even the fastest single drives can only spin the bytes under
>the drive's head at around 3 million bytes/sec.
>	So, isn't a 5.33 million bytes/sec 16-bit slot on the ISA bus pretty
>much up to the task of delivering and retrieving data to and from a
>single hard drive that is only capable of spinning the data off or onto
>the platters at a 3 million bytes/sec rate?

Ever heard about "intelligent drives", ie drives which buffer a couple
of 100kbyte in their internal memory? That's when data transfer from
the HD is similar to data transfer from the (video) memory - the
faster the better.

>	And isn't it expensive overkill to provide a 132 million bytes/sec
>truck (local bus) to haul 3 million bytes/sec freight ( a fast hard drive's
>maximum, spin-limited data transfer rate)?  Seems like that expensive local 
>bus truck will be sitting idle almost 98% of the time. Even the cheaper
>ISA bus truck will be idle almost 44% of the time.

Sorry, I disagree with this and all the rest. Your argument comes from
the days when computers were expensive and woMEN were cheap.
The whole idea of a PC is that it sits there and waits as long as the
operator thinks, but as soon as the operator ask for action, it acts.
As fast as possible.
I have heard secretaries complaining about the 10 sec startup time of
their word processing. You better give everybody the fastest
affordable computer, or they will be mad. Even your wife.

So buy a computer like you would buy a stereo. Take your favourite CD
(program) and shuffle it in the player (computer). If don't see the
difference between $100 and $300 device, the $200 are wasted.
And if you are really interested in numbers, read the computer
magazines. Not that anybody understands them.
If you really want it technical, and you read German, read the "ct
- Magazin fuer Computertechnik" 2/93, p97. You know why I think they are so
good? Because the few selected articles they translate from Byte are
the worst they publish. Nothing to do with me being German, no no.

Sorry if I've got carried away, but this discussion really gets to
me.

Harald Geiger
hgg@ecs.soton.ac.uk