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MAILBAG Upgrading a 486 I recently had the experience of installing AMD 5x86-133 CPUs in two 486 motherboards, one a Chic­ ony brand, the other a Biostar with a UMC chipset, neither of which was designed with a 586 CPU in mind. The AMD 5x86-133 CPU can be made to work in a motherboard not specifically designed for it by jumpering it as per an AMD DX4-100 “plus” or “enhanced” CPU; ie one with power management functions. Jumpering it as a plain AMD or Intel DX4-100 will not work. Choose a 3.45V supply voltage and a 33MHz CPU clock. At this point the BIOS will identify the CPU as an AMD DX4 running at 100MHz. For the CPU to run at its rated 133MHz, a “clock multiplier” jumper must be set. Look for a jumper whose function is “jumper open = 3x clock, jumper closed = 2x clock”. A Biostar manual describes this jumper as “DX/DX4 open, DX2 closed”. A DX4-100 CPU can run (internally) at either 3x or 2x the motherboard clock. Normally the bus clock is set to 33MHz, and the CPU clock = 3x 33 = 99MHz. I suppose one could use a bus clock of 50MHz and CPU clock = 2x 50 = 100MHz. I suspect that the latter combination would result in faster I/O (eg, faster graphics and disc I/O) at the same internal CPU speed. I haven’t tried this, though. A 5x86-133 CPU uses a clock multiplier of either 3x or 4x. In this case, the jumper described above has a slightly different meaning. An open jumper selects a 3x clock as before (99MHz), but a closed jumper selects a 4x clock (133MHz). This jumper may take some finding. For those with a multimeter, one side of this jumper is connected to earth, the other to pin R-17 (CLKMUL) of the CPU. When correctly set, the BIOS sees the CPU as an AMD DX4 “plus” running at 4x 33 = 132 MHz. Be sure to enable write-back mode for the internal CPU cache (16K). I wonder if a system using a clock-doubled 486DX4-100 CPU on a 50MHz bus (assuming this were possible) would be faster than the same system using a 5x86-133 CPU on a 33MHz bus? What about a 586-133 running at 120MHz in clock tripled mode on a 40MHz bus? F. Zabkar, Barrack Heights, NSW. Video security sign has a drawback I have just read the Video Security article on page 62 of the September edition of SILICON CHIP. I feel that anyone contem­ plating using the sign on page 67 should consider the following scenario. Having just burgled your neighbour’s home, burglars about to burgle yours are confronted by this sign. Now they must burgle your home in order to retrieve the tape linking them with the neighbour’s burglary. If after ransacking your home they are unable to locate the tape, their options are limited, one being to torch your home in order to destroy the evidence. A safer solution for a low security site such as a home is a sign that reads: “This property is under VIDEO SURVEILLANCE with Off-Site Recording”. Any VCR used for recording should be well-hidden. If the power meter box is not secure, then a UPS (low cost computer type may be adequate) should be used to power the VCR, cameras, etc. Although probably unnecessary for a home but certainly of value for shop and business surveillance is a dummy VCR complete with tape placed in a prominent position. This tape may be easily taken by or handed over (under threat) to a burglar. K. Forknall, Northlands, WA. Backing up is important Referring to your editorial in the July 1997 issue of SILI­CON CHIP, I think you hit the nail right on the head. Many people don’t even think of or are even told about backups. This could be due to the view of sales people assuming that the purchaser will only use the machine for trivial or unimport­ ant tasks; eg, playing games. In many cases the machine will work OK for a long period of time but one day it may play up. What’s the next step? – try to find what’s caused the corruption and get a backup disc out and restore the corrupted files. If you don’t have a backup the data is unrecoverable and you’ll never see it again. Even with disc repair utilities such as Norton’s this will not guarantee to get any or all of your data back! I recently purchased a backup tape drive for my machine to complement an already numerous set of backup floppy discs. Desp­ite this, a couple of months ago I lost a file due to corruption and ended up recreating it from a printout because the corruption had unknowingly been saved and both machine and floppy had the corrupted file. You can never be too cautious! S. Sidoti, Lilyfield, NSW. Burst charging does the job I have been evaluating Nicad Battery Charger designs lately with the intention of building two permanent installations for domestic use. Two articles from SILICON CHIP have been brought to my attention, these being in the May 1994 and October 1995 is­sues. Both these featured projects using the Philips TEA 1100 IC which, if I have read and understood both articles correctly, rely on “Delta V” voltage detection to terminate normal charge mode and progress to trickle charge. The reason I mention these two articles is that I have also read the excellent article by Horst Reuter from Smart FastCharg­ers in the January 1996 issue of SILICON CHIP. In his article he mentions that he is of the opinion that once the charge voltage peak is reached and the voltage levels out, any nicad battery still charging in the normal charge mode and which reaches the point where the voltage starts to drop (the “Delta V” continued on page 7 November 1997  3