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COMPUTER BITS BY JENNIFER BONNITCHA Why it takes so long to turn on Ever wondered why your computer takes so long between the time you turn it on and the time when it is actually ready to do your bidding? This month we explain why. Start-up is a very busy time in the day-to-day life of your PC. One of the most important activities is the POST (Power On Self Test) which is a series of program routines, buried in the motherboard ROM (Read Only Memory). POST tests all the main system components at power-on time and is th,e reason why there is some delay between turning the computer's power on and actually using it; all tests are executed before the computer loads the operating system. The procedure tests all the primary computer components such as the CPU (Central Processing Unit - the "brains" of your computer), ROM, motherboard support circuitry, memory and major peripheral devices such as printers. However, the tests are brief in nature, to the extent that the POST process can provide error or warning messages when a faulty component is encountered, either by sounding a tone and/or displaying a message. Almost all manufacturers also display the system memory as it is tested. The last number you see (eg, 640KB OK) is the amount of memory correctly tested and the number should agree with the total amount of memory installed in your computer. Alternatively, you may see "conventional" then extended memory tested and reported as separate amounts. Watch next time you boot your computer and note also that expanded memory is not tested by the POST, nor does it count in the numbers reported. For a discussion of PC memory usage, refer to Brian Richard's article in the December 1990 issue of SILICON CHIP. POST error codes POST error codes usually provide tones with varying combinations of beeps to identify the faulty compo- Table 1: Error Tones TONE PROBABLE FAULT No beep Continuous beep Repeating short beeps 1 long, 1 short beep 1 long, 2 short beeps 1 short beep, bad/no display 1 short beep, no boot sequence Power supply Power supply Power supply Motherboard Video adpator card Video cable &/or display Disc cable, adaptor drive nent. If an error is detected during the POST procedure, an error message displays. These messages are usually in the form of a numeric code several digits long and will again depend on your computer's manufacturer. Normal POST completion sounds one short beep when the system starts. If any problems are encountered, you will probably get the tones shown in Table 1 but, as always, watch the screen and check the manual: In addition to the POST, general diagnostics and advanced diagnostics are available for most PCs. Diagnostics discs The manufacturer's System Diagnostics Disc (or equivalent) enables you to test various parts of your computer system, including the system unit and many installed options such as the expansion unit, keyboard, display, printer and so on. You often need to boot from the diagnostics disc to run the programs since a special version of DOS (Disk Operating System) resides on the disc. Of particular interest is the suppression of system parity checking during the boot process using this disc. A normal system may be continually locked up with a memory parity-check error. By disabling the check, a defective system may be able to "limp" through the diagnostics. For "technician level" diagnostics, the Advanced Diagnostics or the equivalent provide the "real" diagnostic programs which produce error messages in the form of numbers. Since many manufacturers offer their own versions of diagnostics programs, you should use those provided. If your system does not have this type of manufacturer support, you can generally use the IBM diagnostics. FEBRUARY1991 37 COMPUTER BITS - CTD Nearly all PC error codes for the POST are represented by the device number followed by two digits other than 00. The device number plus 00 is used to indicate successful completion of a test. Typical error codes are shown in Table 2. The Advanced Diagnostics do a good job with the system components, however these programs fall short when testing disc drives. Drives are the cause of the vast majority of problems in computer systems, so it is worthwhile finding a program to test not only the disc's data but also characteristics such as the drive's alignment. While many programs can evaluate the condition of, say, a floppy disc, not many can evaluate the condition of the drive itself. To do this, you need a disc created by a specially calibrated machine. This disc, which contains certain known errors, can then determine the capabilities of the drive against the disc in conjunction with the appropriate software. Errors can include sectors that are progressively further from the precise track centre, so the ability of the drive to read these intentionally off-centre sectors is used to guage the drive 's alignment. Basic booting As the computer initialises, ROM performs the POST and reads the contents of the Basic Input/Output System (BIDS). The function of the BIDS.SYS file is to talk to the system's peripherals. The IBM PC of old also contained Cassette BASIC, so if all else fa iled, you could play around with BASIC. Placing a small, but very essential part of start-up procedure in ROM allows the computer to boot itself automatically and yet remain flexible for future changes. While an in-depth knowledge of the various kinds of ROM is useful perhaps to a programmer, at some stage it is likely you may need to know which version of ROM is installed in your computer. New ROM ANTRIM ~ TRANSFORMERS versions deal with the ability to interface to the enhanced 101 keyboard, 5.25-inch 1.2Mb drive, 3.5 -inch 720Kb and 1.44Mb drives, hard disc types etc. Subtle differences hidden in your system can often be the cause of some strange problems. ROM version can be tracked through programs such as Norton Utilities and at a basic level through observation at boot time. For example, Phoenix Software manufactures compatible ROM BIDS chips for compatible motherboard manufacturers. A typical display is as follows: Phoenix 80286 ROM BIDS Ver. 3.05TB Copyright (c) 1985,1986 Phoenix Technologies Ltd. All Rights Reserved. If the display changes too quickly for you to read the information, try pressing AS (hold down Ctrl and press the letter S) or the Pause key on the 101 enhanced keyboard. Disc duties Having satisfied itself that the POST memory and hardware tests are complete, the next phase in the boot sequence is to search for a system disc with the operating system on it. A E-1 LAMINATED POWER TRANSFORMERS PCB MOUNT STOCK RANGE TRANSFORMERS, ILABLE PCB mount ex-stock in sizes from 2.5VA to 25VA with secondary voltages from 2 x 6V to 2 x 20V. Triple output models also available for logic circuits. Chassis mount manufactured to order in sizes from 2.5VA to 1KVA in E-1 and C core. CHASSIS MOUNT TO ORDER We are the largest ex-stock supplier of toroidal power transformers in Australia. Our standard range consists of the U.K. manufactured AN,:_RIM range in 10 VA sizes from 15VA to 625VA. All have a single 240V primary and dual secondary windings ranging from 2 x 6V to 2 x 55V. Our local manufacturing facilities supplement this range by manufacturing specials to order. Models are available from stock to suit most project kits. Comprehensive data sheets are available on request. Enquiries from resellers and manufacturers are welcomed. Prices are extremely competitive and generous trade discounts apply for quantity. 38 SILICON CHIP 90 George St., HORNSBY NSW disc qualifies if it has a boot record on the first track of the disc to indicate the presence of the hidden system files 10.COM and DOS.COM - machine language COMmand files. Should the first available disc not contain these two hidden files - you accidentally leave a disc in Drive A, for example - a NON SYSTEM DISK message displays. The first hidden file is 10.COM (or IBMIO.COM if you have the real article). This file contains extensions to the ROM BIOS routines and so by interfacing with it, can pass instructions to the processor and so determine equipment status, initialise peripherals, etc. It also loads the COMMAND. COM file into its allotted memory address. The second hidden file is MSDOS.COM (IBMDOS.COM). This file contains the DOS service routines which are the next level of system software up from ROM BIOS. Its functions include performing 1/0 (input/ output) operations to various devices, initialising the working tables of DOS, and performing its interrupt functions. Additionally, DOS.COM determines the lowest available address for COMMAND.COM to be loaded into Random Access Memory (RAM). CONFIG.SYS file Next, the contents of the CONFIG.SYS file are read from the system disc. SYS files are used by the operating system and they can hold software routines that control and communicate with the computer's devices or peripherals. This file generally contains default values for the operating system and information on required device drivers. The command processor COMMAND.COM is the highest level of DOS and its job is to interpret the commands a user enters through the keyboard and control the internal DOS commands. The internal commands are frequently-used DOS commands such as COPY, DIR, DEL etc that are kept in RAM. COMMAND.COM can't control external commands such as FORMAT, CHKDSK, etc and they must be loaded into memory from a disc whenever they are issued by the user. Executable files COM files are machine language command files. Thus, whenever you type a DOS command, DOS searches Table 2: Typical Error Codes CODE DESCRIPTION 01x 02x 1x~ 2xx 3xx 4xx 5xx 6xx 7xx 9xx 10xx 11 XX 12xx 13xx 14xx 15xx Undetermined problem Power supply System board Memory (RAM) Keyboard Monochrome Display Adaptor (MDA) Colour Graphics Adaptor (CGA) Floppy drive/adaptor 8087, 80287 or 80387 math co-processor Parallel printer adaptor Alternate parallel printer adaptor Asynchronous communications adaptor Alternate asynchronous communications adaptor Game control adaptor Matrix printer Synchronous Data Line Control (SDLC) communications adaptor Display emulation (327x, 5520, 525x) Fixed disc 1/0 expansion unit 3270 PC attachment card Binary synchronous communications (BSC) adaptor Alternate binary synchronous communications adaptor Cluster adaptor Enhanced Graphics Adaptor (EGA) XT/370 errors AT/370 errors 3278/79 emulation adaptor Colour/graphics printer Primary PC network adaptor Secondary PC network adaptor Compact printer errors General Purpose Interface Bus (GPIB) adaptor Data acquisition adaptor Professional graphics controller Voice communications adaptor 3.5-inch external disk drive IBM Expanded Memory Adaptor (XMA) Music feature card 16xx 17xx 18xx 19xx 20xx 21xx 22xx 24xx 26xx 27xx 28xx 29xx 30xx 31xx 33xx 36xx 38xx 39xx 71xx 73xx 85xx 89xx the disc and any path you set for a file with that command name. If the search fails, DOS then searches for a file with the same name and an EXE (EXEcutable) extension. You could say that binary notation EXE files are second-level command files since they are used less frequently· than the COM files. Finally, if an AUTOEXEC.BAT file is found, the information contained within is processed and the computer is ready for use. Next month, we'll have a look at the CONFIG.SYS and ANSI.SYS files, together with a whole host of environment settings you can try on your computer. But be warned: the earlier your DOS version, the less you can try. SC FEBRUARY1991 39