Scor­pio News


January–March 1988 – Volume 2. Issue 1.

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but the increased speed wasn’t echoed elsewhere, the hard disk strolled along at a leisurely 65mS (average seek time) and I guess it took more time getting and storing results than it did actually doing the computing bit. Also, it used standard video cards so the ability to manipulate the video using standard DOS calls wasn’t any better. There’s been a tendency lately to promote 80386 based AT clones as ordinary AT types with ‘Go faster’ stripes. All well and good, but what a waste of the potential crunching power of the 80386, mind you, there isn’t exactly a lot of software to make use of the 80386 in its native mode yet! Maybe I’m wrong, but it looks to me as if this year the advertisers and hype boys will all be jumping on the “Get the speed up and the price down’ band wagon. If you actually need the speed, it’ll still cost a fortune for 23mS voice coil hard disks and super fast video and peripheral cards. Perhaps it’s all sour grapes on my part, in the space of a year my computer which was one of the fastest around at the time, has now been overtaken by machines which will go twice as fast and actually cost less. Still, mine’s got a 35mS hard disk, so for most of the stuff I do these days (database crunching) it’s still faster than the latest ‘Go faster’ toy fitted with the ubiquitous Seagate ST-255 drives.

This brings me neatly round to another topic, actually deciding how fast a computer is going. One of my commercial lumps of software has to use real time clocking to make it work. In other words, it has to have precision delays in the software and rather better than the nominal 18 ‘ticks’ a second clock built into the IBM. The piece of machinery it has to drive has to have timing intervals as short as 1/50th of a second, and is very fussy and makes expensive noises if it gets it wrong. As the software is supplied for any number of IBM clones, ranging from the Amstrad PCW1512 (cheapest) and the IBM XT (slowest) through to one which is running on a Compaq 386 (fastest and most expensive). I’ve been faced with the problem of deciding how fast a computer actually crunches.

The software to produce the delay is simple, it’s nicked from NAS­SYS, and is Richard Beal’s TDEL routine, but instead of counting down a 16 bit number in HL in the Z80, I count down a 48 bit number in the BX, CX and DX registers in the 8086. The actual number to count is set up in a little data table which is created when the software is initialised and in each case, it is finally trimmed by trial and error with a special little delay routine and a good old fashioned stop-watch over a period of about five minutes. The problem is – faced with an unknown computer, brand X, how fast does it actually go, as opposed to how fast do the manufacturers say it goes.

Ok, so over a period of time, I’ve built up a table of likely numbers for different types of computer: an AT at 6MHZ with one wait state is 1.000, a 4.77MHz XT is 0.3564 – and so on. These numbers give me ball park figures to get down to the final business of honing the number with a stop-watch. But what if I don’t know the ball park figure? In my travels I’ve collected a number of speed testing programs.

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