Thanks for the memory.
The current regulatory climate requires that today's labs become more productive with fewer resources. Lost in the glamour of acquiring the latest desktop muscle machine, we often overlook possibilities for expanding the capabilities of older computers. Contrary to popular belief, older computers rarely become nothing more than doorstops. Dr. Siguel's recent MLO article on installing a larger hard drive is an excellent example of expanding the utility of an older computer by making more storage available.
This two-part article examines computer memory and the ways we can use it more effectively. In the final analysis, it is the way we use our time, and the manner in which we apply our resources, that will define what we can accomplish.
* Types of memory. Computers contain two types of memory: read only memory (ROM) and random access memory (RAM). While their physical construction and uses are different, both function similarly.
For both, memory circuits are contained in specialized chips that come in various sizes from 16 kilobytes (KB) to several megabytes (MB); one KB = 1,024 bytes; one MB = 1,024 KB. Each memory chip stores information as a string of binary (1 or 0) values that are translated by the computer into information. Regardless of whether the information is spreadsheet data or the operating code for a video display, it is stored the same way.
ROM is reserved for programs that are essential to the computer's operation. The basic input-output system (BIOS), for example, is a set of instructions saved in ROM that tells the computer what its internal parts are and how to communicate with them. The video ROM contains a set of instructions that tell the computer how to send information to the monitor. Also contained in ROM are programs that are used to interpret signals from the keyboard and that control input and output (IO) ports, such as for a printer or modem. Normally, one cannot alter ROM memory and the contents are not erased when you turn off the computer. ROM memory chips cannot be reprogrammed without special equipment, so they cannot be used for general data storage by the computer.
The motherboard, the large circuit board into which everything else in the computer is plugged, was designed to accommodate one kind of central processing unit (CPU). The first MS-DOS machines contained the 8088 series of CPU chips manufactured by the Intel Corp. (Portland, Ore.). These chips are still used in the PC-XT class machines supplied as part of some reagent quality control programs.
The IBM PS/2 contains the Intel 80286 CPU chip. Newer machines contain 80386 or 80486 CPU chips. With each successive generation of CPU chips, speed increased and the instruction set within the CPU became more sophisticated.
Along with increasing speed and sophistication came more RAM. RAM is where the computer stores the user's software programs and data. Unlike ROM, RAM is erased when you turn off your computer. Most PCs sold today come with at least 640 KB of RAM memory, in contrast to older machines that came with 256 KB and later with 512 KB.
It is interesting to note that the original 8088 CPU was designed for 1,024 KB (i.e., 1 MB). The 80286 CPUs were designed for 16 MB, and the 80386 and 80486 CPUs were designed to hold up to 1,024 MB (i.e., 1 gigabyte) of information, though the machines are commonly sold with only 2-4 usable MB.
Intel released the 80586 CPU, The Pentium, in May 1993. Like the 80386 and 80486, the 80586 chip can address 1 gigabyte of information. Because of an expanded instruction set, most Pentium computers come with 6 to 8 MB of ROM memory. Less memory would be sufficient but pointless (like installing street tires on a race car).
Most computers run a self-diagnostic program that includes a check of memory before booting the drive. Turn on your computer and check the numbers that appear in the upper left corner as the computer runs its internal diagnostics; the rapidly changing counter shows the available memory as it is checked. After the computer has completed its boot-up procedure, you can run CHKDSK to check the amount of available memory in the computer. CHKDSK will report the number of bytes of total and free memory. Then divide the number of bytes by 1,024 to determine the number of kilobytes.
* Running out of memory. At some point, almost everyone runs out of memory and watches helplessly as a file they've been working on disappears. At this point, one can either break the data file into several smaller files or find a way to increase available memory beyond the standard 640 KB. One solution is to add memory to your computer; another is to use existing memory more efficiently, assuming you have 1 MB or more. The second approach costs less and does not require you to alter anything in the computer.
It is a reasonably simple matter to upgrade the RAM memory in an older computer to 640 KB, and it can be well worth doing. RAM chips are standardized according to speed and memory size and can be used in a variety of computers. They are commonly changed in sets of nine chips, frequently called D-RAM chips. Sockets for RAM below 640 KB are usually found on the motherboard. Memory chips between 640 KB and 1 MB vary in location depending upon the machine. Memory above 1 MB is usually placed on a specific memory board, particularly in machines with 8088 CPUs.
Some RAM chips come soldered into a special circuit board, commonly referred to as a single in-line memory module or SIMM; SIMMs contain nine D-RAM chips. Even though they can be used for memory that is below 1 MB on some machines, SIMMs are most commonly used for memory above 1 MB in machines with 80386 and 80486 CPUs. SIMMs are commonly configured as 1 MB, 2 MB, or 4 MB.
Memory chips also come in various speeds. Common speeds are 300 nanoseconds (ns), 150 ns, 120 ns, 100 ns, and lower. Faster chips (e.g., 60 ns versus 100 ns) and those with more memory usually cost more. (NS actually refers to the clock speed of the memory chip, specifically, the length of time to complete one on-off cycle.) A typical price for 9 D-RAM chips with 256 KB, 100 ns would be $12 to $14 from a computer mail order firm. A typical price for a 1 MB, 100 ns SIMM would be $35 to $50.
Unlike D-RAM chips, SIMMs tend to be machine- and CPU-specific, so that information needs to be supplied when ordering. Memory boards are available for about $130 to $400 without chips. Boca Industries (Boca Raton, Fla.) and Intel both make several plug-in memory boards that are widely available. Memory boards are available for 8088, 80286, 80386, and 80486 CPUs; some can be used on more than one type of computer.
* Adding memory. Adding memory chips to your computer's motherboard or adding a memory board is not a difficult task, but you do have to pay strict attention to some key details. When adding memory chips, be certain that the new chips are of the same speed or faster than the chips that are already in the machine. Otherwise, you may experience some incompatibility problems.
Another problem is static electricity, which will destroy virtually any microcomputer chip. Make sure that you ground yourself and your computer before working on it. The following steps were suggested to me by my local computer repair shop:
1. Turn off the computer and remove the power plug from the wall socket. This will completely remove all electrical power to the machine.
2. Remove the cover from the computer.
3. Reconnect the 3-wire power cord and plug it back into a grounded socket. CAUTION: Beware of potentially exposed terminals on the power switch since they will now have full-line voltage applied. Do not turn on the computer with the cover open. The important thing is to ensure that the computer chassis is grounded.
4. Ground yourself by touching the power supply case. (It's the silver box with ventilation holes that encloses the power supply.)
5. Insert your D-RAM chips, SIMM boards, or memory boards into the appropriate socket(s). A D-RAM chip has a small notch or round depression at one end that should line up with a corresponding notch on the receiving socket. The pins on a D-RAM chip are fragile, so line up everything before rocking the chip into place. Special chip pulling pliers and insertion tools are available for a few dollars and are well worth the price.
6. Disconnect the power cord from line voltage and then replace the case.
7. Turn on the computer and check the total memory.
Alternatively, ask people in your biomedical services department or your local computer store to perform the service for you. The job requires little time of an expert.
* Memory addresses. Regardless of how much RAM or ROM a machine has, each location in memory has a specific address. Memory addresses are a number sequence from zero to the highest amount of memory the CPU is capable of addressing. Thus, a memory address will exist for every byte the CPU was designed to use, even if some of the memory is not being employed.
Loading information into RAM is a process of placing each bit of data at a specific memory address. The kinds of things that get loaded include:
1. The disk operating system (DOS), which determines how the computer will interact with its files and disk drives.
2. Statements concerning various devices, buffers, file size, and general operating conditions, sometimes called "environments," which the user has determined are required. These statements are usually found in the CONFIG.SYS and AUTOEXEC.BAT files that the computer reads and executes upon booting.
3. Any background programs that pop up upon pressing a designated hot key. Such programs are called terminate and stay resident (TSR) programs and include things like schedulers, calculators, and a variety of utilities.
4. The program you want to run, that is your spreadsheet, word processing, or database program, for example.
5. The actual data that are entered (e.g., workload recording data, a lab procedure, an inventory database, or QC data).
CONFIG.SYS and AUTOEXEC.BAT
When an IBM-compatible computer is turned on, it runs through a self-diagnostic check and then attempts to load the disk operating system (DOS) from the default drive. This drive must have the following three programs or their equivalents: IO.SYS, MSDOS.SYS, and COMMAND.COM. These programs are placed on the start-up, or boot disk, with the FORMAT d:/S command (where d: is the drive to be formatted). They must all be from the same version of DOS.
After the system has loaded the three programs, it will look for a file called CONFIG.SYS that specifies variable parameters for certain operating conditions. The CONFIG.SYS file also contains device statements that are additional programs to control various hardware functions. The typical CONFIG.SYS file looks like this:
device=c:\DOS\ANSI.SYS files=15 buffers=15
While not essential, this file is almost always found in the root directory of the disk with the three system files above. It is easy to edit since it is an ASCII text file and is accessible through almost every word processing program.
After running CONFIG.SYS, the system will look for a file called AUTOEXEC.BAT. Also a text file, this lists a variety of "environmental" statements, such as the path the system should take to find commonly used programs, what the cursor should look like, and what program to run first. A typical AUTOEXEC.BAT looks like this:
echo off PATH C:\;C:\BAT\;C:\DOS (where to look for things) prompt $p$g (how the prompt will look) GETCLOCK (get the date and time) SET PCTOOLS=C:\TOOLBOX\PCTOOLS\DATA (where to find PCTOOLS) SHELL (run SHELL, a menu program)
1. Siguel EN. How to upgrade your hard disk drive. (Computer Dialog) MLO. April 1993; 25(4): 51-54.
Flynn J. Ten Minute Guide to Memory Management. Carmel, Ind: Alpha Books Division of Prentice Hall Computer Publishing; 1992.
Goodman JM. Memory Management for All of US. Carmel, Ind: SAMS Division of Prentice Hall Computer Publishing; 1993.
William Sottile, Ph.D., D(ABMM) is laboratory director of Upper Peninsula Laboratory, Michigan Department of Public Health, Houghton, Mich.