Parity Errors
• Parity errors indicate that memory is bad.
• First if the computer has memory expansion board, determine if the faulty chip is on the memory board or the motherboard.
• If the memory error came up during the RAM check it will stop at the number at which the faulty chip is located.
• If the fault is with the memory card, hopefully a RAM chip testing program will have come with the card when purchased it. This program will locate and often display graphically where the faulty chip is. If you don’t have such a program use the same procedure as outline on the succeeding notes.
• It is hard to track down the exact chip which is bad on the motherboard because each BIOS (which sends the error message) for the clone uses different error message coding. Finding the faulty chip can be a tedious task.
• Take all out memory cards.
• Try pressing down on all the RAM chips on the motherboard, sometimes corrosion will affect the contacts and cause the parity error. Pressing down on the chips helps seat the chips and improve the connections.
• Take out the last bank of chips and change the DIP switches to reflect any changes in the amount of memory installed.
• Replace memory one at a time. Turn the computer after installing each chip to see if a parity error pops up. If it does, you know you have found the bad chip. Replace any bad chip(s) with the new one.(s).
Computer Memory (Random Access Memory)Ram consists of computer chips which store information. They are installed in rows called banks of nine on the motherboard. Only 8 chips per row are used So store data while the 9th is used for parity checking Data transfer between the CPU and RAM occurs at the fastest possible rate since it involves no moving parts as do hard and floppy disk drives.Types of RAM
-Dynamic RAM (DRAM) is (he type of memory most often used. It is, “volatile” meaning (hat it will retain data only as long as the computer is turned on. Any loss of power (even a momentary flicker in electricity) and the data in RAM will vanish. When DRAM is used in a system, additional circuitry is required to refresh the information periodically;
- Static RAM (SRAM) is not a very common form of memory because it is expensive. It has the advantage however of being able to retain data with the use of a battery. If a memory system is small static devices are used because of the additional cost of the refreshing circuit in DRAM. The break-even point seems to be about 16K bytes of memory. Memory system containing more than 16K bytes will generally be dynamic, while system;; containing loss memory will be static.
The speed of RAM chips is measured in nanoseconds (nS); one nanosecond equals a billionth of a second. The speed of RAM installed into the computer must match with the computers’ speed. If the improper speeds are used, the overall operation of the computer will be slowed or the entire system may lock up. The following lists the speed of RAM chips needed with each CPU speed.
- 4.77 MHz CPU needs 200 nS RAM chips ”, ” 8 MHz CPU needs 150 nS RAM chips , - 10 MHz CPU needs 120 nS RAM chips
Current Ram Capacities are 128MB, 256 MB, 512mb. and there is now 1 gig RAM.
As much as you can afford, get the highest RAM for your Computer, the higher the better.
Memory Expansion Cards
The requirements for memory keeps going up. Software application programs need more and more memory to operate efficiently, MS-DOS unfortunately has the ability to access 640 K of memory directly. There are however some schemes which have been devised to indirectly get around the memory limits of DOS.
- Expanded. Memory Specifications (EMS) - This was the first scheme to allow computers to use more memory. II was written in 1985 by Lotus, Intel, and Microsoft. ‘
Enhanced Expanded Memory Specifications (EEMS) - This competing and improved standard was created by other some other largo’ computer product manufacturers; namely AST, Quadram and Ashlon-Tate. This standard was better for multitasking applications than EMS.
- Expanded Memory Specification (EMS) 4.0 - All the companies supporting the previous two standard got together and merged the previous standard into yet expanded memory standard called EMS 4.0. This is now the expanded memory standard on which everyone has agreed, It allows for the use of up to 32 megabytes, the use of larger application software and use of multitasking. It works,on all generation of computers as well.
You may have experienced having your computer intermittently hangs-up, or may re-boot itself for no apparent reason. This can be annoying, and can mean you have lost valuable work that you we in the process of creating.
If this has happened once, then your chances of explaining the cause are remote in the extreme. If you find it happening regularly, then it is clearly in your interest to find and fix the problem.
There are a few things you can check for yourself that may save you a trip to the repair shop.
With most modern computers, the system comes with built in circuitry to monitor the state of the computer. One of the checks built into your system is to test the operating temperature. The computer may shut down if this moves outside the desirable operating range.
For your system to run at the correct operating temperature it is important that air circulates freely in and around the case. If you have the computer case installed inside an enclosure, then this may be the first thing to consider changing. Similarly, I have seen computers covered with books, manuals and paper documents. These again can hinder air circulation, and these items should be removed. Take a look at the slotted vents in the sides of the case. These slots can become blocked by an accumulation of dust. Because the computer is usually always drawing some power, it has a constant electrostatic charge. A computer is second only to a vacuum cleaner in its ability to suck in dust and fluff.
Taking the cover of the case will also show the dust build-up inside the computer. Be careful removing dust accumulations from internal components. This is probably best done with a soft artist’s brush or an aerosol can of compressed air.
Next, take a look at the internal cooling fans. Modern computer usually have a cooling fan perched on top of the processor. This fan should be clear of dust, and running freely, without obvious scraping noises, when the computer is operating. It is OK to start the computer with the case cover removed, just be careful not to poke things into the various components. There will also be a cooling fan inside or attached to the power supply. This again should be free of dust and running freely. Some computers may also have an additional case fan. This will be screwed on over one of the slotted case vents, and typically be running from a cable connected to the mother board. Not all machines have a separate case fan, but if it is there, it is there for a reason. Apply the same checks to this fan.
If you have identified faults with your cooling fans, this may require a trip to your local repair shop. The repair technician may also suggest that the CPU heat sink be removed and re-placed with fresh heat transfer compound, which is a straightforward job for an experienced repairer.
