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COMPUTER BITS By JENNIFER BONNITCHA Adding RAM to your computer Software expands to fill the available memory, to paraphrase a familiar adage. If you have a computer, sooner or later you will want or need ·more memory. Adding it is usually a matter of plugging in RAM chips and then resetting the motherboard DIP switches. The story of how the computer shrank in size from that of a room to the silicon chip is now familiar to most computer users. The technology for producing microchips was originally very expensive, so early computer memories were initially small. Computer programs in those "olden days" were designed to OC7 cupy a minimum of memory space. The trend since has been towards more memory and more functions in less space. First there was the integrated circuit (IC), then Large Scale Integration (LSI) and now Very Large Scale Integration (VLSI). Integration in this context means that functions previously located on different chips are now incorporated as part of one microchip. The chip itself is made of a semiconductor, usually silicon, which has been etched and plated. The pattern etched on the surface is that of the integrated circuits. First the pattern is drawn large, generally using computer-aided drafting (CAD), and then reduced in size. The modern computer has electronic circuits which use the binary number system for all operations. The binary system consists only of the digits O (zero) and 1 (one); the "on" state can be defined as 1, the "off" state as 0. 70 SILICON CHIP The smallest part of the binary system is called a bit (Blnary digiT). All information in the computer is stored in bits, however different computers process the information at different rates. Most chips are designed to receive, process and send one bit of information at a time. Eight bits make a byte. Each byte can have 256 different values from 0 through to 255. Data is moved in bytes around the computer system through eight wires known as the parallel data bus or more usually, just the data bus; each wire carries one bit of the 8-bit byte. All bytes used by the computer are stored in a special memory location and each location has a unique address. The Central Processing Unit (CPU) is the "brain" of the computer. The original IBM computer used Intel's 16-bit microprocessor, the 8088. This processor operates internally on 16 bits of data at a time but transfers the data 8 bits at a time to and from the external devices. Memory chips are thus assembled in multiples of 8, plus one extra for parity checking. Thus, while the 8088 is described as having an 8-bit data bus, it is generally considered a 16-bit processor. The AT computer is based on the Intel 80286 which is a true 16-bit processor. Information is transferred 16 bits at a time so the memory chips are installed in multiples of 16 bits with 2 bits for parity checking. Finally, the newer 386 computers have a 32-bit processor which also has RAM on a proprietary memory board. This highly specialised memory contributes significantly to the high performance of the 386. The main memory area of the personal computer is called Random Access Memory (RAM). The CPU is capable of asking for data directly at any address, rather than sequentially locating the information, as is the case with, say, a cassette tape. Adding memory Many users purchase a computer system and then decide to enhance the original hardware. For the majority of users, particularly considering today's memory-hungry applications, the first choice is to add additional memory. Although computer memory has, in fact, several different components, expanding memory generally refers to one type of memory - RAM. Officially, RAM on the IBM PC XT is expandable only to 640K. However with larger amounts of RAM, spreadsheet programs such as Lotus 1-2-3 can have larger worksheets, desktop publishing programs such as Ventura can run the Professional Extension, and integrated .programs such as Excel just take up a lot of memory space. Increased RAM also can be allocated to a "RAM disc" which is a virtual, electronic disc drive. The advantage is that the disc drive, POWER SOCKET PARALLEL PORT FLOPPY DISC CONTROLLER Adding extra memory to your computer is simply a matter of installing additional RAM chips in the sockets on the motherboard. Always use the correct memory chips and be sure to install them the right way around. typically drive E, can be used for the system at the same rate. temporary data storage. It is useful Chip speed is measured in for storing frequently used sections nanoseconds (ns). A nanosecond is of a program, and since it is much one billionth (10 - 9) of a second. faster than conventional mechanOne megahertz (1MHz) is one Jcal disc drives, program execution · million ticks (cycles) of the CPU is considerably faster. clock per second. Thus one clock cycle at 1MHz is equal to 1 microseMemory speed cond or 1,000 nanoseconds. 10MHz is 10 times faster with clock cycles Each computer is designed to use (or windows) of 100ns. RAM chips of a certain minimum XTs manufactured after 1983 speed. Memory specifications are had a processor speed of 4. 77MHz typically described by capacity, and thus a minimum access speed speed and type. While it is possible of 200ns. However, memory chips to substitute slower chips for the then were in the range of 200 to correct type, you then run the risk 300ns. To compensate, a "wait of jeopardising the integrity of the state" was added to make the data moved through the chips. 200ns window twice as wide at Similarly, there is seldom any ad400ns. The fast 386 processors of vantage in purchasing chips which today zoom through work at 25MHz significantly exceed the computer with ticks of the CPU clock only 40 manufacturer's specifications. The nanoseconds long. processor still operates at the same speed, passing information through Speeding up operation of the computer seems to be a neverending story. The latest step is the invention of a special kind of circuit called "cache memory". The circuit monitors information passing between main memory and the processor. Each time the processor sends information to memory, the cache circuit grabs a copy and stores it away. Should the processor again call for the same information, it is delivered at high speed to the processor. When this occurs, the processor experiences no waiting, so the operation is referred to as "zero wait state". If the information is not available, cache memory remains silent and the processor communicates with memory in the usual manner. Typically, the memory cache is measured in increments of 32K and it is generally better to use smaller DECEMBER1989 71 Switch 1 QI 2 3 4 5 6 7 8 ~□ ~□ □□□□□ Position 1 7-8 2 34 5-6 Position Function Amount of memory options installed Always in the off position rather than larger caches. Amongst other reasons, the smaller cache takes less time to fill up. Memory options IBM PCs manufactured prior to 1983 used 16K RAM modules with one module of nine chips always installed at the factory. Thus, the minimum on-board memory for these models was 16K. Memory expansion for these systems was obtained by installing up to three additional kits of 16K each. Each kit contained nine 16K bit chips. PCs manufactured after mid1983 and the PC XTs all use '64K memory chips. Each has four rows of sockets on its system board. The PCs come with a minimum of 64K bytes of memory, which means that up to three additional 64K memory kits can be installed. The XTs have a minimum memory of 128K and can accommodate up to two additional 64K memory kits. Once the system board of the PC or XT is filled, RAM memory can only be expanded by the use of memory adapter cards. Installing three memory kits in your PC raises the amount of on board memory to either 64K or 256K bytes of storage, as the actual 72 96KB 1 □ 0□□ 00001 1 □□□□ 0000 1 128KB 10 0□□ 00001 lo□M □o □ ol 160KB 100□□ 000011 □□□□ 00001 Function Number of 5'/4-inch diskette drives installed Reserved for co-processor Amount of RAM on system board Type of monitor you are using Switch 2 1-2-3-4 5-6-7-8 MEMORY OPTIONS SILICON CHIP D□ □□ ODDI I □□□□ 00001 228KB 1□ 0□□ 00001 1□□□□ 00001 256KB I□ o□ □ oo □ ol lo □□ □ oo □ol 196KB ID Fig.1: the DIP switches on the motherboard must be reset if you install extra RAM. These diagrams show the settings for switches 1 & 2 in the IBM PC but you should always check the manual for your particular machine. amount is dependent on whether 16K or 64K chips are used in the upgrade. Adding 64K memory kits to the XT raises the on-board memory from 128K to 192K or 256K bytes. Once this limit is reached, RAM cards or multifunction boards can increase the XT's memory beyond 256K, usually to the maximum addressable by the DOS operating system - 640K. Although 640K is the minimum required for use in today's memoryhungry environment, for the ATstyle computer, 1Mb or more of memory is not beyond reason, especially when you deal with large spreadsheets or desktop publishing applications. It seems that when/if the OS/2 and UNIX-style multitasking operating systems really come to the fore, computers will require around 2MB of memory just to work, let alone run any applications! Memory is added to the AT system board in 128K increments, up to a maximum of 1.2Mb. The AT memory expansion options include 128K memory expansion option, a 256K memory expansion kit and 512K expansion options. Again, RAM cards or multifunction boards may be added to the system unit to increase memory to 16Mb. Parity As noted above, each row or bank of memory on the PC consists of nine chips. Eight of the chips represent the eight bits in the data byte, while the last chip is used for memory parity checking. This extra bit of information is usually added to each character specifically for error checking purposes. Parity is computed by adding up the number of "1" bits in a data field. An even number of ls would result in a "1" as the parity bit, while an odd number would give a "O". The result of the addition is called the parity checksum, and parity checking is the most basic form of error checking. Should a problem arise, there is a roughly 50% chance the computer will realise this since the parity check bit will not match. Live in fear of the DOS message "Parity Error at 1000:lFOF" since this indicates a defective chip. If you ever do get this dread message, writing down the address will help determine which memory chips are defective. Sockets for the RAM chips are located near the bottom of the system unit. The location is easily identified by the labels on the system board, eg: XT Bank 0, Bank 1, Bank 2 & Bank 3. AT Bank 0, Bank 1. Banks O and 1 already contain chips on older versions of the XT while Banks 2 and 3 on these machines are empty. If only 64K of memory is added, the chips are placed in Bank 3. On the basic AT, Bank O contains 256K and Bank 1 is empty. When you install a chip, note the small notch or dot on one end of the chip. This identifies pin 1. In memory banks, this end always faces the same direction, so make sure the chips you install · do likewise. To install a chip, place it over the corresponding socket then tilt slightly so that one row of pins matches the appropriate holes. This done, gently push the pins on the opposite side into the holes, then push the chip firmly down into the socket. DIP switch settings After installing the additional memory, you must also alter the DIP switches located on the system board below and to the right of the expansion slots. This is to allow the computer to recognise the additonal memory (see Figs.1 & 2). Once the extra memory space on the system board has been filled to capacity (256K on the XT and 512K on the AT), you can add further RAM by installing a RAM or multifunction card. Memory options for the AT, such as the 512K memory expansion card, are inserted into an available slot. Amaximum of five cards may be installed to typically combine parallel and serial interfaces with other features such as additional RAM. We've already mentioned the advantages of the extra RAM and you frequently receive a bonus with these types of boards in the form of extra software which allows the spare memory to be used for tasks such as "print spooling". Thus, print information is stored in the extra RAM and by so doing, main RAM and the rest of the computer is freed to perform other tasks while the slow process of controlling the print functions is performed. ~ Switch I 2 3 4 5 6 7 8 "' of~ lJ □ □ □ □ □ □ Position 2 3-4 5-6 7-8 Function For normal operation is off Co-processor Amount of RAM on system board Type of monitor you are using Number of 5 ¼-inch diskette drives installed Memory options K I □ □□□ ODDO I I □ 0~ coo DO I K IOD□ □ DO DO I 128K 192 256 D.DAUNER ELECTRONIC COMPONENTS WE STOCK A WIDE RANGE OF ELECTRONIC PARTS for • Development • Repair • Radio Amateur • Industrial Electronic • Analog and Digital WHILE STOCKS LAST NEOSID HELIX FILTER for UHF now available COAXIAL RELAY 28VDC $32.00 TRANSMITTER VALVE 5786 $18.00 Come and see. Showroom: 51 Georges Crescent, Georges Hall, NSW 2198 (Behind Caltex Service Station In Blrdwood Road) Phone 724 6982 TRADING HOURS: Monday to Friday 9.00 a.m. to 4.00 p.m. Saturday from 9.00 a.m. to 12.00 noon. * GREAT VALUE AND TECHNOLOGY * COMPUTER PRODUCTS ... AT·4000 Motherboard 12MHz 80286 AT ulg for XT. $489 AT,4000 System 12MHz 512K 101Kbd, 200W, PS etc $1499 ECI VGA ·16 EGA , CGA, HGA modes Card 800x600x16 Res. . $399 AHOOO MB 25MHz 80386 inc 018M 32·bit Mem Exp Board $1989 . $802.06 ECl.fAX for XTIAT . . $399 2S&P $85; FDC $97.2;; 101KBD $88.43; ED·CGMA $99; VGA MON $775; 1.2MB FDD $161.20; 1.44MB FDD $181.35; CASE & 200W PS $207; SAVE 30% OH INDUSTRIAL CONTROL CARDS . . . EC111 6511 2MHz SBC with AID DIA Clk 8at. $336 EC109 6809 CPU 2MHz w/Clk Bat 2 x RS232 Cent 1/F . $304 EC545 Colour Crt (RGB) 16k/4 page SRAM 512 Char . $238 EC·1F124 IND CONTRLR Forth 1D·bit AID, DIA Opto lsol $392 LEDS 3mm & 5mm (Min 1OD/type) ... Red $0.05; Red HB $0.08; Green $0.07; Yellow $0.08; Orange $0.08 DIODES (Min 100/type) . .. IN4001; 1N4004 ; 1N914; 1N4 148 . $0.05 OTHER BITS .. . GAL PAL Programmer - 1 only - WAS $750 . . .. NOW $400 G65SC02·2 . $3.90 G65SC51 ·2 . . $4.00 SRAM Batt B/up Skt - Convert SRAM to non vol . . $19.95 QUALITY DISKETTES_(Pkt of 10, 100% error free , Lltime G/tee) 51/," DSDD 360K . .$ 6.25 51/,"DSHD 1.:/MD .. . ~17.88 3½" DSOO 720K . . $19.75 DSHD 1.44Mb . ... . $39.99 P&P $8.50 PRICES INGL. SALES TAX Fig.2: there's only one DIP switch to worry about on the XT's motherboard. Set positions 3 & 4 as shown to correspond to the amount of on-board memory. 26 Boron St, Sumner Park, Brisbane, Qld 407 4 Ph: (07) 376 2955 Fax: (07) 376 3286 WELLINGTON HZ: Ph: (04) 85 8742 Fax: (04) 82 8850 Ken Curry Managing Director DECEMBER1989 73