Upgrading & Repairing PCs Eighth Edition processors--require Socket 7.

Pentium Pro (P6) motherboards use Socket

-------------------------------------------------------------------------- 8, and many are set up for multiple processors. Before going to the
- expense of buying a multi-processor board, ensure that your operating
system is able to handle it. For instance, while Windows 95 cannot
really benefit from more than one CPU, Windows NT, OS/2, and some
- 4 - others may run considerably faster.

* Motherboard Speed. A Pentium or Pentium Pro motherboard should run at

Motherboards 60 or 66MHz and be speed-switchable between these speeds. Notice that
all the Pentium and Pentium Pro processors sold today run at a
multiple of the motherboard speed. For example, Pentium 75 runs at a
* Replacement Motherboards motherboard speed of 50MHz; Pentium 60, 90, 120, 150, and 180MHz chips
* Knowing What to Look for (Selection Criteria) run at a 60MHz base motherboard speed; and the Pentium 66, 100, 133,
o Documentation 166, and 200 run at a 66MHz motherboard speed setting. The Pentium Pro
150, 180, and 200 run at 50, 60, and 66MHz speeds, respectively. All
* Rom BIOS Compatibility components on the motherboard (especially cache memory) should be
o OEMs rated to run at the maximum allowable motherboard speed.
o AMI * Cache Memory. All Pentium motherboards should have 256K to 512K of
o Award Level 2 cache on-board. Most Pentium Pro processors have a built-in
256K or 512K Level 2 cache, but may also have more Level 2 cache on
o Phoenix the motherboard for even better performance. The Level 2 cache should
* Using Correct Speed-Rated Parts be of a Write-Back design, and must be populated with chips that are
* Motherboard Form Factors fast enough to support the maximum motherboard speed, which should be
15ns or faster for 66MHz maximum motherboard speeds. For Pentium
o Backplane Systems boards, the cache should be a Synchronous SRAM (Static RAM) type,
o Full-Size AT which is also called Pipelined Burst SRAM.
o Baby-AT * SIMM Memory. All Pentium and Pentium Pro motherboards should use
o LPX either 72-pin SIMMs or 168-pin DIMMs (Dual In-line Memory Modules).
Due to the 64-bit design of these boards, the 72-pin SIMMs must be
o ATX installed in matched pairs, while DIMMs are installed one at a time
o NLX (one per 64-bit bank). Carefully consider the total amount of memory
that the board supports. While 16M is regarded as a bare minimum for
* Motherboard Interface Connectors today's memory-hungry applications, you may actually require much
* Motherboard CMOS RAM Addresses more. Pentium motherboards should support at least 128M, and many
-------------------------------------------------------------------------- current Pentium II boards support more than 1G! A motherboard should
- contain at least four memory sockets (72-pin, 168-pin, or a
combination) and the more the better. For maximum performance, look
Easily the most important component in a PC system is the main board or for systems that support SDRAM (Synchronous DRAM) or EDO (Extended
motherboard. Some companies, such as IBM, refer to the motherboard as a Data Out) type SIMMs/DIMMs. The SIMMs should be rated at 70ns or
system board or planar. The terms motherboard, main board, system board, faster.
and planar are interchangeable. In this chapter, we will examine the
different types of motherboards available, as well as those components Mission-critical systems ideally should use Parity SIMMs and ensure that
usually contained on the motherboard and motherboard interface connectors. the motherboard fully supports parity checking or even ECC (Error
Correcting Code) as well. Note that the popular Intel Triton Pentium
Replacement Motherboards chipset (82430FX) does not support parity checked memory at all, but their
other Pentium chipsets such as the older Neptune (82430NX) and newer Triton
Some manufacturers go out of their way to make their systems as physically II (82430HX) do indeed offer parity support. Triton II even offers ECC
incompatible as possible with any other system. Then replacement parts, capability using standard parity SIMMs. All the current Pentium Pro
repairs, and upgrades are virtually impossible to find--except, of course, chipsets also support Parity memory and are ideal for file servers and
from the original system manufacturer, at a significantly higher price other mission critical use when equipped with parity SIMMs or DIMMs.
than
the equivalent part would cost to fit a standard PC-compatible system. * Bus Type. Pentium, Pentium Pro, and Pentium II motherboards should
have three or four ISA bus slots and three or four PCI local bus
For example, if the motherboard in my current AT-chassis system (or any slots. Take a look at the layout of the slots to ensure that cards
system using a Baby-AT motherboard and case) dies, I can find any number inserted in them will not block access to memory sockets, or be
of blocked by other components in the case.
replacement boards that will bolt directly in, with my choice of
processors * BIOS. The motherboard should use an industry-standard BIOS such as
and clock speeds, at very good prices. If the motherboard dies in a newer those from AMI, Phoenix, Microid Research, or Award. The BIOS should
IBM, Compaq, Hewlett-Packard, Packard Bell, Gateway, AST, or other be of a Flash ROM or EEPROM (Electrically Erasable Programmable Read
proprietary shaped system, you'll pay for a replacement available only Only Memory) design for easy updating. The BIOS should support the
from Plug and Play (PnP) specification, Enhanced IDE or Fast ATA, as well
the original manufacturer, and you have little or no opportunity to select as 2.88M floppy drives. APM (Advanced Power Management) support should
a board with a faster or better processor than the one that failed. In be built into the BIOS as well.
other words, upgrading or repairing one of these systems via a motherboard
replacement is difficult and usually not cost-effective. * Form Factor. For maximum flexibility, the Baby-AT form factor is still
a safe bet. It can be installed in the widest variety of case designs,
Knowing What to Look For (Selection Criteria) and is retrofittable in most systems. For the greatest performance and
future flexibility, many newer motherboards and systems incorporate
As a consultant, I am often asked to make a recommendation for purchases. the new ATX form factor, which has distinct performance and functional
Making these types of recommendations is one of the most frequent tasks a advantages over Baby-AT. Additionally, the new NLX form factor has
consultant performs. Many consultants charge a large fee for this advice. been developed by Intel as an improvement on the ATX. Although it is
Without guidance, many individuals don't have any rhyme or reason to their new, the NLX specification is supported by a number of manufacturers,
selections and instead base their choices solely on magazine reviews or, so it could prove to be a popular board in the coming years.
even worse, on some personal bias. To help eliminate this haphazard
selection process, I have developed a simple checklist that will help you * Built-in interfaces. Ideally, a motherboard should contain as many
select a system. This list takes into consideration several important built-in standard controllers and interfaces as possible (except
system aspects overlooked by most checklists. The goal is to ensure that video). A motherboard should have a built-in floppy controller that
the selected system truly is compatible and has a long life of service and supports 2.88M drives, built-in primary and secondary local bus (PCI
upgrades ahead. or VL-Bus) Enhanced IDE (also called Fast ATA) connectors, two
built-in high-speed serial ports (must use 16550A type buffered
It helps to think like an engineer when you make your selection. Consider UARTs), and a built-in high-speed parallel port (must be
every aspect and detail of the motherboards in question. For instance, you EPP/ECP-compliant). A built-in PS/2 type mouse port should be
should consider any future uses and upgrades. Technical support at a included, although one of the serial ports can be used for a mouse as
professional (as opposed to a user) level is extremely important. What well.
support will be provided? Is there documentation, and does it cover
everything else? Some newer systems, particularly those with ATX and NLX form factors,
should include a built-in USB (Universal Serial Bus) port. USB ports
In short, a checklist is a good idea. You can use the following check list will become a "must-have" item on multimedia systems in the near
to evaluate any PC-compatible system. You might not have to meet every one future. A built-in SCSI port is a bonus as long as it conforms to ASPI
of these criteria to consider a particular system, but if you miss more (Advanced SCSI Programming Interface) standards. Built-in network
than a few of these checks, consider staying away from that system. The adapters are acceptable, but usually an ISA slot card network adapter
items at the top of the list are the most important, and the items at the is more easily supported via standard drivers and is more easily
bottom are perhaps of lesser importance (although I think each item is upgraded as well. Built-in video adapters are also a bonus in some
important). The rest of this chapter discusses in detail the criteria in situations, but because there are many different video chipset and
this checklist: adapter designs to choose from, generally there are better choices in
external local bus video adapters. The same goes for built-in sound
* Processor. A Pentium motherboard should use as a minimum the cards; they usually offer basic Sound Blaster compatibility and
second-generation 3.3v Pentium processor, which has a 296-pin Socket function, but often do not include other desirable features found on
5 most plug-in sound cards, such as wavetable support. Plug and Play
or Socket 7 configuration that differs physically from the 273-pin (PnP). The motherboard should fully support the Intel PnP
Socket 4 first-generation design. Pentium motherboards with the specification. This will allow automatic configuration of PCI adapters
Socket as well as PnP ISA adapters.
7 configuration also support newer processors with MMX technology,
including AMD's K6. All second-generation Pentiums (75MHz and up) are -------------------------------------------------------
fully SL Enhanced. Newer Pentium Pro and Pentium II processors have TIP: Even if a motherboard doesn't list that it's
their own unique motherboard configurations, and are not compatible PnP-compatible, it may be. PCI motherboards are
with other Pentium-based motherboards. required to be PnP-compatible, as it is a part of the
PCI standard.
* Processor Sockets. A Pentium motherboard should have at least one ZIF -------------------------------------------------------
socket that follows the Intel Socket 7 (321-pin) specification. The
Socket 7 with an adjacent VRM (Voltage Regulator Module) socket will * Power Management. The motherboard should fully support SL Enhanced
allow the best selection of future Pentium processors that will be processors with APM (Advanced Power Management) and SMM (System
available at higher speeds. Although Socket 5 is similar to Socket 7, Management Mode) protocols that allow for powering down various system
many of the newer and faster Pentiums--including the MMX equipped components to different levels of readiness and power consumption.
 be available for download from the Internet.
* Motherboard Chipset. Pentium and Pentium MMX motherboards should use
a Several companies have specialized in the development of a compatible ROM
high-performance chipset--preferably one that allows parity checking, BIOS product. The three major companies that come to mind in discussing ROM
such as the Intel Triton II (430HX). The popular original Intel BIOS software are American Megatrends, Inc. (AMI), Award Software, and
Triton Phoenix Software. Each company licenses its ROM BIOS to a motherboard
(430FX) chipset, along with the newer 430TX and 430VX chipsets, does manufacturer so that the manufacturer can worry about the hardware rather
not support parity-checked memory. For critical applications using than the software. To obtain one of these ROMs for a motherboard, the OEM
Pentium motherboards where accuracy and data integrity is important, must answer many questions about the design of the system so that the
I proper BIOS can be either developed or selected from those already
recommend you use a board based on the Triton II (430HX) chipset or designed. Combining a ROM BIOS and a motherboard is not a haphazard task.
any others like it that support ECC memory using true parity memory No single, generic, compatible ROM exists, either. AMI, Award, Microid
modules. As a bonus, the 430HX chipset supports USB and dual CPUs, Research, and Phoenix ship to different manufacturers many variations of
making it truly versatile. their BIOS code, each one custom-tailored to that specific system, much
like DOS can be.
Pentium Pro and Pentium II motherboards currently have the high-end
Orion (450KX and 450GX) chipsets, as well as the less expensive A good source of information on currently available BIOS products is
Natoma available from the System Optimization Web site at:
(440FX) chipset. All three chipsets support parity memory, USB, and
multiple CPUs, and are suitable for critical application use. http://www.sysopt.com/bios.html

* Documentation. Good technical documentation is a requirement. AMI.

Documents should include information on any and all jumpers and
switches found on the board, connector pinouts for all connectors, Although AMI customizes the ROM code for a particular system, it does not
specifications for cache RAM chips, SIMMs, and other plug-in sell the ROM source code to the OEM. An OEM must obtain each new release as
components, and any other applicable technical information. I would it becomes available. Because many OEMs don't need or want every new
also acquire separate documentation from the BIOS manufacturer version developed, they might skip several version changes before licensing
covering the specific BIOS used in the system, as well as the data a new one.
books covering the specific chipset used in the motherboard.
Additional data books for any other controller or I/O chips on-board The AMI BIOS is currently the most popular BIOS in PC systems today. Newer
are a bonus, and may be acquired from the respective chip versions of the AMI BIOS are called Hi-Flex due to the high flexibility
manufacturers. found in the BIOS configuration program. The AMI Hi-Flex BIOS is used in
Intel, AMI, and many other manufacturers' motherboards. One special AMI
Another nice thing to have is available online support and feature is that it is the only third-party BIOS manufacturer to make its
documentation updates, although this should not be accepted in place own motherboard.
of good hardcopy manuals.
During powerup, the BIOS ID string is displayed on the lower-left of the
You may notice that these selection criteria seem fairly strict and may screen. This string tells you valuable information about which BIOS version
disqualify many motherboards on the market, including what you already you have, as well as certain settings which are determined by the built-in
have setup program.
in your system! These criteria will, however, guarantee you the highest
quality motherboard offering the latest in PC technology that will be -----------------------------------------------------------------
upgradable, expandable, and provide good service for many years. Most of TIP: A good trick to help you view the BIOS ID string is to shut
the time I recommend purchasing boards from better-known motherboard down and either unplug your keyboard, or hold down a key as you
manufacturers such as Intel, SuperMicro, Micronics, AMI, Biostar, Tyan, power back on. This will cause a keyboard error, and the string
Asus, and so on. These boards might cost a little more than others that will remained displayed.
you -----------------------------------------------------------------
have never heard of, but there is some safety in the more well-known
brands; that is, the more boards that they sell, the more likely that any The primary BIOS Identification string (ID String 1) is displayed by any
problems will have been discovered by others and solved long before you AMI BIOS during the POST (Power On Self-Test) at the bottom-left corner of
get the screen, below the copyright message. Two additional BIOS ID strings (ID
yours. Also, if service or support are needed, the larger vendors are more Strings 2 and 3) can be displayed by the AMI Hi-Flex BIOS by pressing the
likely to be around in the long run. Insert key during POST. These additional ID strings display the options
that are installed in the BIOS.
Documentation
The general BIOS ID String 1 format for older AMI BIOS versions is shown in
As mentioned, extensive documentation is an important factor to consider Table 4.1.
when you're planning to purchase a motherboard. Most motherboard
manufacturers design their boards around a particular chipset, which Table 4.1 ABBB-NNNN-mmddyy-KK
actually counts as the bulk of the motherboard circuitry. There are a
number of manufacturers offering chipsets, such as Intel, Opti, VIA, SiS, PositionDescription
and others. I recommend obtaining the data book or other technical A BIOS Options:
documentation on the chipset directly from the chipset manufacturer. D = Diagnostics built-in.
S = Setup built-in.
One of the more common questions I hear about a system relates to the BIOS E = Extended Setup built-in.
Setup program. People want to know what the "Advanced Chipset Setup" BBB Chipset or Motherboard Identifier:
features mean and what the effects of changing them will be. Often they go C&T = Chips & Technologies chipset.
to the BIOS manufacturer thinking that the BIOS documentation will offer NET = C&T NEAT 286 chipset.
help. Usually, however, people find that there is no real coverage of what 286 = Standard 286 motherboard.
the chipset setup features are in the BIOS documentation. You will find SUN = Suntac chipset.
this information in the data book provided by the chipset manufacturer. PAQ = Compaq motherboard.
Although these books are meant to be read by the engineers who design the INT = Intel motherboard.
boards, they contain all the detailed information about the chipset's AMI = AMI motherboard.
features, especially those that might be adjustable. With the chipset data G23 = G2 chipset 386 motherboard.
book, you will have an explanation of all the controls in the Advanced NNNN The manufacturer license code reference number.
Chipset Setup section of the BIOS Setup program. mmddyy The BIOS release date, mm/dd/yy.
KK The AMI keyboard BIOS version number.
Besides the main chipset data books, I also recommend collecting any data
books on the other major chips in the system. This would include any The BIOS ID String 1 format for AMI Hi-Flex BIOS versions is shown in Table
floppy 4.2.
or IDE controller chips, Super I/O chips, and of course the main
processor. Table 4.2 AB-CCcc-DDDDDD-EFGHIJKL-mmddyy-MMMMMMMM-N
You will find an incredible amount of information on these components in
the data books. PositionDescription
A Processor Type:
----------------------------------------------------------------- 0 = 8086 or 8088.
CAUTION: Most chipset manufacturers only make a particular chip 2 = 286.
for a short time, rapidly superseding it with an improved or 3 = 386.
changed version. The data books are only available during the 4 = 486.
time the chip is being manufactured, so if you wait too long, you 5 = Pentium.
will find that such documents may no longer be available. The 6 = Pentium Pro.
time to collect documentation on your motherboard is now! B Size of BIOS:
----------------------------------------------------------------- 0 = 64K BIOS.
1 = 128K BIOS.
ROM BIOS Compatibility CCcc Major and Minor BIOS version number.
DDDDDD Manufacturer license code reference number.
The issue of ROM BIOS compatibility is important. If the BIOS is not 0036xx = AMI 386 motherboard, xx = Series #.
compatible, any number of problems can result. Several reputable companies 0046xx = AMI 486 motherboard, xx = Series #.
that produce compatibles have developed their own proprietary ROM BIOS 0056xx = AMI Pentium motherboard, xx = Series #.
that 0066xx = AMI Pentium Pro motherboard, xx = Series #.
works just like IBM's. Also, many of the compatibles' OEMs have designed E 1 = Halt on Post Error.
ROMs that work specifically with additional features in their systems F 1 = Initialize CMOS every boot.
while G 1 = Block pins 22 and 23 of the keyboard controller.
effectively masking the effects of these improvements from any software H 1 = Mouse support in BIOS/keyboard controller.
that would "balk" at the differences. I 1 = Wait for <F1> key on POST errors.
J 1 = Display floppy error during POST.
OEMs. K 1 = Display video error during POST.
L 1 = Display keyboard error during POST.
Many OEMs (Original Equipment Manufacturers) have developed their own mmddyy BIOS Date, mm/dd/yy.
compatible ROMs independently. Companies such as Compaq and AT&T have MMMMMMMMChipset identifier or BIOS name.
developed their own BIOS products which are comparable to those offered by N Keyboard controller version number.
AMI, Phoenix, and others. These companies also offer upgrades to newer
versions that often can offer more features and improvements or fix AMI Hi-Flex BIOS ID String 2 is shown in Table 4.3.
problems with the older versions. If you use a system with a proprietary
ROM, make sure that it is from a larger company with a track record and Table 4.3 AAB-C-DDDD-EE-FF-GGGG-HH-II-JJJ
one
that will provide updates and fixes as necessary. Ideally, upgrades should PositionDescription
 AA Keyboard controller pin number for clock switching. on the version of BIOS you have.
B Keyboard controller clock switching pin function:
H = High signal switches clock to high speed. The second area in which Phoenix excels is the documentation. Not only are
L = High signal switches clock to low speed. the manuals that you get with the system detailed, but also Phoenix has
C Clock switching through chip set registers: written a set of BIOS technical-reference manuals that are a standard in
0 = Disable. the industry. The set consists of three books, titled System BIOS for IBM
1 = Enable. PC/XT/AT Computers and Compatibles, CBIOS for IBM PS/2 Computers and
DDDD Port address to switch clock high. Compatibles, and ABIOS for IBM PS/2 Computers and Compatibles. Phoenix is
EE Data value to switch clock high. one of few vendors who has done extensive research on the PS/2 BIOS and
FF Mask value to switch clock high. produced virtually all the ROMs in the PS/2 Micro Channel clones on the
GGGG Port Address to switch clock low. market. In addition to being an excellent reference for the Phoenix BIOS,
HH Data value to switch clock low. these books serve as an outstanding overall reference to any company's
II Mask value to switch clock low. IBM-compatible BIOS. Even if you never have a system with a Phoenix BIOS, I
JJJ Pin number for Turbo Switch Input. highly recommend these books.

AMI Hi-Flex BIOS ID String 3 is shown in Table 4.4. Micronics motherboards have always used the Phoenix BIOS, and these
motherboards are used in many of the popular name-brand compatible systems.
Table 4.4 AAB-C-DDD-EE-FF-GGGG-HH-II-JJ-K-L Phoenix has been one of the largest OEMs of Microsoft MS-DOS. If you have
MS-DOS, you also have the Phoenix OEM version. Phoenix licenses its DOS to
PositionDescription other computer manufacturers so long as they use the Phoenix BIOS. Because
AA Keyboard controller pin number for cache control. of its close relationship with Microsoft, it has had access to the DOS
B Keyboard controller cache control pin function: source code, which helps in eliminating compatibility problems.
H = High signal enables the cache.
L = High signal disables the cache. Although Phoenix does not operate a technical support service by itself,
C 1 = High signal is used on the keyboard controller pin. their largest nationwide distributor does, which is Micro Firmware Inc.
DDD Cache control through Chipset registers: Online information is available at http://www.firmware.com, or check the
0 = Cache control off. phone numbers listed in the vendor list in Appendix B. Micro Firmware
1 = Cache control on. offers upgrades to many systems with a Phoenix BIOS, including many Packard
EE Port address to enable cache. Bell, Gateway 2000 (with Micronics motherboards), Micron Technologies, and
FF Data value to enable cache. other systems.
GGGG Mask value to enable cache.
HH Port address to disable cache. Unless the ROM BIOS is a truly compatible, custom OEM version such as
II Data value to disable cache. Compaq's, you might want to install in the system the ROM BIOS from one of
JJ Mask value to disable cache. the known quantities, such as AMI, Award, or Phoenix. These companies'
K Pin number for resetting the 82335 memory controller. products are established as ROM BIOS standards in the industry, and
L BIOS Modification Flag: frequent updates and improvements ensure that a system containing these
0 = The BIOS has not been modified. ROMs will have a long life of upgrades and service.
1-9, A-Z = Number of times the BIOS has been modified.
A good source of online information about BIOS basics can be found at:
The AMI BIOS has many features, including a built-in setup program
activated by pressing the Delete or Esc key in the first few seconds of http://www.lemig.umontreal.ca/bios/bios_sg.htm
booting up your computer. The BIOS will prompt you briefly as to which key
to press and when to press it. The AMI BIOS offers user-definable hard Using Correct Speed-Rated Parts
disk
types, essential for optimal use of many IDE or ESDI drives. The newer Some compatible vendors use substandard parts in their systems to save
BIOS money. Because the CPU is one of the most expensive components on the
versions also support Enhanced IDE drives and will auto- configure the motherboard, and many motherboards are sold to system assemblers without
drive parameters. the CPU installed, it is tempting for the assembler to install a CPU rated
for less than the actual operating speed. A system could be sold as a
A unique AMI BIOS feature is that, in addition to the setup, it has a 100MHz system, for example, but when you look "under the hood," you may
built-in, menu-driven, diagnostics package--essentially a very limited find a CPU rated for only 90MHz. The system does appear to work correctly,
version of the stand-alone AMIDIAG product. The internal diagnostics are but for how long? If the company that manufactures the CPU chip installed
not a replacement for more comprehensive disk-based programs, but they can in this system had tested the chip to run reliably at 100MHz, it would have
help in a pinch. The menu-driven diagnostics does not do extensive memory labeled the part accordingly. After all, the company could sell the chip
testing, for example, and the hard disk low-level formatter works only at for more money if it worked at the higher clock speed.
the BIOS level rather than at the controller register level. These
limitations often have prevented it from being capable of formatting When a chip is run at a speed higher than it is rated for, it will run
severely damaged disks. hotter than it would normally. This may cause the chip to overheat
occasionally, which would appear as random lockups, glitches, and
The AMI BIOS is sold through distributors, a list of which is available at frustration. I highly recommend that you avoid systems whose operation
http://www.ami.com/distributor.html. You may also contact Washburn and speed exceeds the design of the respective parts.
Co.,
listed in the vendor list in Appendix A. However, keep in mind that you This practice is easy to fall into because the faster rated chips cost more
cannot buy upgrades and replacements direct from AMI. money, and Intel and other chip manufacturers usually rate their chips very
conservatively. I have taken several 25MHz 486 processors and run them at
Award. 33MHz, and they seemed to work fine. The Pentium 90 chips I have tested
seem to run fine at 100MHz. Although I might purchase a Pentium 90 system
Award is unique among BIOS manufacturers because it sells its BIOS code to and make a decision to run it at 100MHz, if I were to experience lockups or
the OEM and allows the OEM to customize the BIOS. Of course, then the BIOS glitches in operation, I would immediately return it to 90MHz and retest.
no longer is Award BIOS, but rather a highly customized version. AST uses If I purchase a 100MHz system from a vendor, I fully expect it to have
this approach on its systems, as do other manufacturers, for total control 100MHz parts, not 90MHz parts running past their rated speed! These days,
over the BIOS code, without having to write it from scratch. Although AMI many chips will have some form of heat sink on them, which helps to prevent
and Phoenix customize the ROM code for a particular system, they do not overheating, but which can also sometimes cover up for a "pushed" chip. If
sell the ROM's source code to the OEM. Some OEMs that seem to have the price is too good to be true, ask before you buy: "Are the parts really
developed their own ROM code started with a base of source code licensed manufacturer-rated for the system speed?"
to
them by Award or some other company. To determine the rated speed of a CPU chip, look at the writing on the
chip. Most of the time, the part number will end in a suffix of -xxx where
The Award BIOS has all the normal features you expect, including a built- the xxx is a number indicating the maximum speed. For example, -100
in indicates that the chip is rated for 100MHz operation.
setup program activated by pressing Ctrl+Alt+Esc. This setup offers
user-definable drive types, required in order to fully use IDE or ESDI -----------------------------------------------------------------
hard CAUTION: Be careful when running software to detect processor
disks. The POST is good, and Award runs technical support on its Web site speed. Such programs can only tell you what speed the chip is
at http://www.award.com. They also run a BBS whose number is listed in the currently running at, not what the true rating is. Also ignore
vendor list in Appendix A. the speed indicator lights on the front of some cases. These
digital displays can literally be set via jumpers to read any
In all, the Award BIOS is high quality, has minimal compatibility speed you desire! They have no true relation to actual system
problems, speed.
and offers a high level of support. -----------------------------------------------------------------

Phoenix. Motherboard Form Factors

The Phoenix BIOS for many years has been a standard of compatibility by There are several compatible form factors used for motherboards. The form
which others are judged. It was one of the first third-party companies to factor refers to the physical dimensions and size of the board, and
legally reverse-engineer the IBM BIOS using a "clean room" approach. In dictates what type of case the board will fit into. The types of
this approach, a group of engineers studied the IBM BIOS and wrote a motherboard form factors generally available are the following:
specification for how that BIOS should work and what features should be
incorporated. This information then was passed to a second group of * Backplane Systems LPX
engineers who had never seen the IBM BIOS. They could then legally write a
new BIOS to the specifications set forth by the first group. This work * Full-size AT ATX
would then be unique and not a copy of IBM's BIOS; however, it would
function the same way. This code has been refined over the years and has * Baby-AT NLX
very few compatibility problems compared to some of the other BIOS
vendors. * LPX

The Phoenix BIOS excels in two areas that put it high on my list of * ATX
recommendations. One is that the POST is excellent. The BIOS outputs an
extensive set of beep codes that can be used to diagnose severe * NLX
motherboard
problems which would prevent normal operation of the system. In fact, this Backplane Systems
POST can isolate memory failures in Bank 0 right down to the individual
chip with beep codes alone. The Phoenix BIOS also has an excellent setup Not all systems have a motherboard in the true sense of the word. In some
program free from unnecessary frills, but that offers all the features one systems, the components normally found on a motherboard are located instead
would expect, such as user-definable drive types, and so on. The built-in on an expansion adapter card plugged into a slot. In these systems, the
setup is activated by pressing either Ctrl+Alt+S or Ctrl+Alt+Esc, board with the slots is called a backplane, rather than a motherboard.
depending Systems using this type of construction are called backplane systems.
 Slots are located on one or both sides of the riser card depending on the
Backplane systems come in two main types: passive and active. A passive system and case design.
backplane means the main backplane board does not contain any circuitry at
all except for the bus connectors and maybe some buffer and driver Another distinguishing feature of the LPX design is the standard placement
circuits. All the circuitry found on a conventional motherboard is of connectors on the back of the board. An LPX board has a row of
contained on one or more expansion cards installed in slots on the connectors for video (VGA 15-pin), parallel (25-pin), two serial ports
backplane. Some backplane systems use a passive design that incorporates (9-pin each), and mini-DIN PS/2 style Mouse and Keyboard connectors. All of
the entire system circuitry into a single mothercard. The mothercard is these connectors are mounted across the rear of the motherboard and
essentially a complete motherboard that is designed to plug into a slot in protrude through a slot in the case. Some LPX motherboards may have
the passive backplane. The passive backplane/mothercard concept allows the additional connectors for other internal ports such as Network or SCSI
entire system to be easily upgraded by changing one or more cards. Because adapters. Figure 4.2 shows the standard form factors for the LPX and
of the expense of the high function mothercard, this type of system design Mini-LPX motherboards used in many systems today.
is rarely found in PC systems. The passive backplane design does enjoy
popularity in industrial systems, which are often rack-mounted. Some FIG. 4.2 LPX and Mini-LPX motherboard form factors.
high-end file servers also feature this design.
ATX
An active backplane means the main backplane board contains bus control
and The ATX form factor is a recent evolution in motherboard form factors. ATX
usually other circuitry as well. Most active backplane systems contain all is a combination of the best features of the Baby-AT and LPX motherboard
the circuitry found on a typical motherboard except for the processor designs, with many new enhancements and features thrown in. The ATX form
complex. The processor complex is the name of the circuit board that factor is essentially a Baby-AT motherboard turned sideways in the chassis,
contains the main system processor and any other circuitry directly along with a modified power supply location and connector. The most
related important thing to know initially about the ATX form factor is that it is
to it, such as clock control, cache, and so forth. The processor complex physically incompatible with either the previous Baby-AT or LPX designs. In
design allows the user to easily upgrade the system later to a new other words, a different case and power supply are required to match the
processor type by changing one card. In effect, it amounts to a modular ATX motherboard. These new case and power supply designs have become
motherboard with a replaceable processor section. Most modern PC systems common, and can be found in many new systems.
that use a backplane design use an active backplane/processor complex.
Both The official ATX specification was released by Intel in July 1995, and has
IBM and Compaq have used this type of design in some of their high-end been written as an open specification for the industry. The latest revision
(server class) systems, for example. This allows an easier and generally of the specification is Version 2.01, published in February 1997. Intel has
more affordable upgrade than the passive backplane/mothercard design since published detailed specifications so other manufacturers can use the ATX
the processor complex board is usually much cheaper than a mothercard. design in their systems.
Unfortunately, because there are no standards for the processor complex
interface to the system, these boards are proprietary and can only be ATX improves on the Baby-AT and LPX motherboard designs in several major
purchased from the system manufacturer. This limited market and areas:
availability causes the prices of these boards to be higher than most
complete motherboards from other manufacturers. * Built-in double high external I/O connector panel. The rear portion of
the motherboard includes a stacked I/O connector area, which is 6.25
The motherboard system design and the backplane system design have both inches wide by 1.75 inches tall. This allows external connectors to be
advantages and disadvantages. Most original personal computers were located directly on the board and negates the need for cables running
designed as backplanes in the late 1970s. Apple and IBM shifted the market from internal connectors to the back of the case as with Baby-AT
to the now traditional motherboard with a slot-type design because this designs.
type of system generally is cheaper to mass-produce than one with the
backplane design. The theoretical advantage of a backplane system, * Single keyed internal power supply connector. This is a boon for the
however, average end user, who always had to worry about interchanging the
is that you can upgrade it easily to a new processor and new level of Baby-AT power supply connectors and subsequently blowing the
performance by changing a single card. For example, you can upgrade a motherboard! The ATX specification includes a single keyed and
system's processor just by changing the card. In a motherboard-design shrouded power connector that is easy to plug in, and which cannot be
system, you often must change the motherboard itself, a seemingly more installed incorrectly. This connector also features pins for supplying
formidable task. Unfortunately, the reality of the situation is that a 3.3v to the motherboard, which means that ATX motherboards will not
backplane design is often much more expensive to upgrade, and because the require built-in voltage regulators that are susceptible to failure.
bus remains fixed on the backplane, the backplane design precludes more
comprehensive upgrades that involve adding local bus slots, for example. * Relocated CPU and memory. The CPU and memory modules are relocated so
they cannot interfere with any bus expansion cards, and they can
Another nail in the coffin of backplane designs is the upgradable easily be accessed for upgrade without removing any of the installed
processor. Intel has designed all 486, Pentium, Pentium MMX, and Pentium bus adapters. The CPU and memory are relocated next to the power
Pro processors to be upgradable to faster (sometimes called OverDrive) supply, which has a single fan blowing air across them, thus
processors in the future by simply swapping (or adding) the new processor eliminating the need for inefficient and failure-prone CPU cooling
chip. Changing only the processor chip for a faster one is the easiest and fans. There is room for a large passive heat sink above the CPU as
generally most cost-effective way to upgrade without changing the entire well.
motherboard.
* Relocated internal I/O connectors. The internal I/O connectors for the
Because of the limited availability of the processor complex boards or floppy and hard disk drives are relocated to be near the drive bays
mothercards, they usually end up being more expensive than a complete new and out from under the expansion board slot and drive bay areas. This
motherboard that uses an industry standard form factor. Intel recently means that internal cables to the drives can be much shorter, and
announced the new NLX form factor for the Pentium II, and it shares some accessing the connectors will not require card or drive removal.
traits with traditional backplane systems. The NLX has been promised
considerable industry support, so we may well see affordable backplane * Improved cooling. The CPU and main memory are cooled directly by the
systems in the near future. power supply fan, eliminating the need for separate case or CPU
cooling fans. Also, the ATX power supply fan blows into the system
Full-Size AT chassis, thus pressurizing it which greatly minimizes dust and dirt
intrusion into the system. If desired, an air filter can be easily
The full-size AT motherboard is so named because it matches the original added to the air intake vents on the power supply, creating a system
IBM AT motherboard design. This allows for a very large board of up to 12 that is even more immune to dirt or dust in the environment.
inches wide by 13.8 inches deep. The keyboard connector and slot
connectors * Lower cost to manufacture. The ATX specifications eliminate the need
must conform to specific placement requirements to fit the holes in the for the rats nest of cables to external port connectors found on
case. This type of board will fit into full-size AT or Tower cases only. Baby-AT motherboards, eliminates the need for additional CPU or
Because these motherboards will not fit into the popular Baby-AT or chassis cooling fans, eliminates the need for on-board 3.3v voltage
Mini-Tower cases, and because of advances in component miniaturization, regulators, uses a single power supply connector, and allows for
they are no longer being produced by most motherboard manufacturers. shorter internal drive cables. These all conspire to greatly reduce
not only the cost of the motherboard, but also significantly reduces
Baby-AT the cost of a complete system including the case and power supply.

The Baby-AT form factor is essentially the same as the original IBM XT Figure 4.3 shows the new ATX system layout and chassis features. Notice how
motherboard, with modifications in screw hole positions to fit into an the entire motherboard is virtually clear of the drive bays, and how the
AT-style case (see Figure 4.1). These motherboards also have specific devices like CPU, memory, and internal drive connectors are easy to access
placement of the keyboard connector and slot connectors to match the holes and do not interfere with the bus slots. Also notice the power supply
in the case. Note that virtually all full-size AT and Baby-AT motherboards orientation and the single power supply fan that blows into the case
use the standard 5-pin DIN type connector for the keyboard. Baby-AT directly over the high heat, generating items like the CPU and memory.
motherboards will fit into every type of case except the Low Profile or
Slimline cases. Because of their flexibility, this is now the most popular FIG. 4.3 ATX system chassis layout and features.
motherboard form factor. Figure 4.1 shows the dimensions and layout of a
Baby-AT motherboard. The ATX motherboard is basically a Baby-AT design rotated sideways. The
expansion slots are now parallel to the shorter side dimension and do not
FIG. 4.1 Baby-AT motherboard form factor. interfere with the CPU, memory, or I/O connector sockets. In addition to a
full-sized ATX layout, Intel also has specified a mini-ATX design as well,
LPX which will fit into the same case. Although the case holes are similar to
the Baby-AT case, cases for the two formats are generally not compatible.
Another popular form factor used in motherboards today is the LPX and The power supplies would require a connector adapter to be interchangeable,
Mini-LPX form factors. This form factor was first developed by Western but the basic ATX power supply design is similar to the standard Slimline
Digital for some of their motherboards. Although they no longer produce PC power supply. The ATX and mini-ATX motherboard dimensions are shown in
motherboards, the form factor lives on and has been duplicated by many Figure 4.4.
other motherboard manufacturers. These are used in the Low Profile or
Slimline case systems sold widely today. These are often lower-cost FIG. 4.4 ATX and Mini-ATX motherboard form factors.
systems
like those sold at retail electronics superstores. It should be noted that Clearly, the advantages of the ATX form factor make it a good choice for
systems using LPX boards may have other differences which can cause high-end systems. For backwards compatibility, Baby-AT is still hard to
compatibility problems similar to those of proprietary systems. beat, and there are still more Baby-AT motherboards, cases, and power
supplies on the market than the ATX versions. With the coming of NLX
The LPX boards are characterized by several distinctive features. The most motherboards and the support that form factor is receiving from the
noticeable is that the expansion slots are mounted on a bus riser card industry, it seems unlikely that ATX will be the all encompassing wave of
that the future.
plugs into the mother- board. Expansion cards must plug sideways into the
riser card. This sideways placement allows for the low profile case For complete specifications, check out the ATX Motherboard Specification
design. page at
 Table 4.8 Parallel Port Pin-Header Connector
http://www.teleport.com/~atx/
Signal Name Pin Pin Signal Name
NLX STROBE- 1 2 AUTO FEED-
Data Bit 0 3 4 ERROR-
NLX is the latest development in desktop motherboard technology, and may Data Bit 1 5 6 INIT-
prove to be the form factor of choice in the near future. It is a Data Bit 2 7 8 SLCT IN-
low-profile form factor similar in appearance to LPX, but with a number of Data Bit 3 9 10 Ground
improvements designed to allow full integration of the latest Data Bit 4 11 12 Ground
technologies. Data Bit 5 13 14 Ground
Whereas the primary limitation of LPX boards includes an inability to Data Bit 6 15 16 Ground
handle the physical size of newer processors, as well as their higher Data Bit 7 17 18 Ground
thermal characteristics, the NLX form factor has been designed ACJ- 19 20 Ground
specifically BUSY 21 22 Ground
to address these problems. PE (Paper End)23 24 Ground
SLCT 25 26 N/C
Specific advantages of the NLX form factor include:
Table 4.9 Motherboard Mouse Pin-Header Connector
* Support for current processor technologies. This is especially
important in Pentium II systems because the size of the Single Edge PinSignal Pin Signal
Contact cartridge this processor uses can limit its use on existing 1 Gnd 5 CLK
Baby-AT and LPX motherboards. Although a few motherboard 2 Data 6 KEY
manufacturers 3 N/C 7 KEY
currently offer ATX-based Pentium II systems, they generally only 4 Vcc 8 N/C
have
room for two 72-pin SIMM sockets! Table 4.10 Infrared Data (IrDA) Pin-Header Connector

* Flexibility in the face of rapidly changing processor technologies. PinSignal Name Pin Signal Name
Backplane-like flexibility has been built into the form by allowing a 1 +5 V 4 Ground
new motherboard to be easily and quickly installed without tearing 2 Key 5 IrTX
your entire system to pieces. But unlike traditional backplane 3 IrRX 6 CONIR (Consumer IR)
systems, many industry leaders are putting their support behind NLX,
including AST, Digital, Gateway, Hewlett-Packard, IBM, Micron, NEC, Table 4.11 Battery Connector
and others.
PinSignal Pin Signal
* Support for other emerging technologies. This includes Accelerated 1 Gnd 3 KEY
Graphics Port (AGP) high-performance graphic solutions, Universal 2 Unused 4 +6v
Serial Bus (USB), and tall memory modules and DIMM technology.
Furthermore, with the emerging importance of multimedia applications, Table 4.12 LED and Keylock Connector
connectivity support for such things as video playback, enhanced
graphics, and extended audio have been built into the motherboard. PinSignal Pin Signal
This should represent a good cost savings over expensive 1 LED Power (+5v) 4 Keyboard Inhibit
daughterboard 2 KEY 5 Gnd
arrangements, which have been necessary for many advanced multimedia 3 Gnd
uses in the past.
Table 4.13 Speaker Connector
Figure 4.5 shows the basic NLX system layout. Notice that, like ATX, the
system is clear of the drive bays and other chassis-mounted components. PinSignal Pin Signal
Also, the motherboard and I/O cards (which, like the LPX form factor, are 1 Ground 3 Board-Mounted Speaker
mounted parallel to the motherboard) can easily be slid in and out of the 2 KEY 4 Speaker Output
side of the chassis, leaving the riser card and other cards in place. The
processor itself can be easily accessed and enjoys greater cooling than in Table 4.14 Microprocessor Fan Power Connector
a more closed in layout.
PinSignal Name
FIG. 4.5 LX system chassis layout and features. 1 Ground
2 +12V
As you can see, the NLX form factor has been designed for maximum 3 Sense tachometer
flexibility and space efficiency. Even extremely long I/O cards will fit
easily, without fouling on other system components as has been such a -----------------------------------------------------------------
problem with Baby-AT form factor systems. CAUTION: Do not place a jumper on this connector; serious board
damage will result if the 12v is shorted to ground.
Complete design specifications and information on NLX boards can be found -----------------------------------------------------------------
online at the official NLX Motherboard Specification page, located at:
Note that some boards have a board mounted piezo speaker. It is enabled by
http://www.teleport.com/~nlx/ placing a jumper over pins 3 and 4, which routes the speaker output to the
board mounted speaker. Removing the jumper allows a conventional speaker to
ATX and NLX form factors will probably be used in most future systems. I be plugged in.
usually do not recommend LPX style systems if upgradability is a factor
because it is not only difficult to locate a new motherboard that will Motherboard CMOS RAM Addresses
fit,
but LPX systems are also limited in expansion slots and drive bays as Table 4.15 shows the information maintained in the 64-byte standard CMOS
well. RAM module. This information controls the configuration of the system and
Baby-AT systems still offer a great deal of flexibility at present, but is read and written by the system Setup program.
for
future systems, ATX and NLX configurations are the way to go. In the original AT system, a Motorola 146818 chip was used. Modern systems
incorporate the CMOS into the chipset, Super I/O chip, or use a special
Motherboard Interface Connectors battery and NVRAM (Non-Volatile RAM) module from companies like Dallas or
Benchmarq. The standard format of the information stored in the CMOS RAM is
There are a variety of different connectors on a modern motherboard. shown in Table 4.15.
Tables
4.5 through 4.14 contain the pinouts of most of the different interface Table 4.15 AT CMOS RAM Addresses
and
I/O connectors you will find. Offset HexOffset Dec Field Size Function
00h 0 1 byte Current second in binary coded decimal
Table 4.5 ATX Motherboard Power Connector (BCD)
01h 1 1 byte Alarm second in BCD
PinSignal Name Pin Signal Name 02h 2 1 byte Current minute in BCD
1 +3.3 V 11 +3.3 V 03h 3 1 byte Alarm minute in BCD
2 +3.3 V 12 -12 V 04h 4 1 byte Current hour in BCD
3 Ground 13 Ground 05h 5 1 byte Alarm hour in BCD
4 +5 V 14 PS-ON# (Power Supply Remote On/Off Control) 06h 6 1 byte Current day of week in BCD
5 Ground 15 Ground 07h 7 1 byte Current day in BCD
6 +5 V 16 Ground 08h 8 1 byte Current month in BCD
7 Ground 17 Ground 09h 9 1 byte Current year in BCD
8 PWRGD (Power Good) 18 -5 V 0Ah 10 1 byte Status register A
9 +5 VSB (Standby) 19 +5 V Bit 7 = Update in progress
10 +12 V 20 +5 V 0 = Date and time can be read
1 = Time update in progress
Table 4.6 Baby-AT Motherboard Power Connectors Bits 6-4 = Time frequency divider
010 = 32.768KHz
PinName Pin Name Bits 3-0 = Rate selection frequency
1 PWRGD (Power Good) 7 Ground 0110 = 1.024KHz square wave
2 +5 V 8 Ground frequency
3 +12 V 9 -5 V 0Bh 11 1 byte Status register B
4 -12 V 10 +5 V Bit 7 = Clock update cycle
5 Ground 11 +5 V 0 = Update normally
6 Ground 12 +5 V 1 = Abort update in progress
Bit 6 = Periodic interrupt
Table 4.7 Serial Port Pin-Header Connectors 0 = Disable interrupt (default)
1 = Enable interrupt
PinSignal Name Pin Signal Name Bit 5 = Alarm interrupt
1 DCD 6 CTS 0 = Disable interrupt (default)
2 DSR 7 DTR 0 = Disable interrupt (default)
3 Serial In - (SIN) 8 RI 1 = Enable interrupt
4 RTS 9 GND Bit 4 = Update-ended interrupt
5 Serial Out - (SOUT) 10 Not Connected 0 = Disable interrupt (default)
1 = Enable interrupt
 Bit 3 = Status register A square wave special CMOS byte called the diagnostics status byte. By examining this
frequency location with a diagnostics program, you can determine whether your system
0 = Disable square wave (default) has set trouble codes, which indicate that a problem has occurred
1 = Enable square wave previously.
Bit 2 = Date format
0 = Calendar in BCD format
(default)
1 = Calendar in binary format
Bit 1 = 24-hour clock
0 = 24-hour mode (default)
1 = 12-hour mode
Bit 0 = Daylight Savings Time Table 4.16 CMOS RAM (AT and PS/2) Diagnostic Status Byte Codes
0 = Disable Daylight Savings
(default) Bit Number
1 = Enable Daylight Savings 7 6 5 4 3 2 1 0Hex Function
0Ch 12 1 byte Status register C 1 . . . . . . .80 Real-time clock (RTC) chip lost power
Bit 7 = IRQF flag . 1 . . . . . .40 CMOS RAM checksum is bad
Bit 6 = PF flag . . 1 . . . . .20 Invalid configuration information found at POST
Bit 5 = AF flag . . . 1 . . . .10 Memory size compare error at POST
Bit 4 = UF flag . . . . 1 . . .08 Fixed disk or adapter failed initialization
Bits 3-0 = Reserved . . . . . 1 . .04 Real-time clock (RTC) time found invalid
0Dh 13 1 byte Status register D . . . . . . 1 .02 Adapters do not match configuration
Bit 7 = Valid CMOS RAM bit . . . . . . . 101 Time-out reading an adapter ID
0 = CMOS battery dead . . . . . . . .00 No errors found (Normal)
1 = CMOS battery power good
Bits 6-0 = Reserved If the Diagnostic status byte is any value other than zero, you will
0Eh 14 1 byte Diagnostic status normally get a CMOS configuration error on bootup. These types of errors
Bit 7 = Real-time clock power status can be cleared by re-running the Setup program.
0 = CMOS has not lost power
1 = CMOS has lost power ---------------------------------------------------------------------------
Bit 6 = CMOS checksum status [Previous chapter][Next chapter][Contents]
0 = Checksum is good
1 = Checksum is bad © Copyright, Macmillan Computer Publishing. All rights reserved.
Bit 5 = POST configuration information
status
0 = Configuration information is
valid
1 = Configuration information is
invalid
Bit 4 = Memory size compare during
POST
0 = POST memory equals
configuration
1 = POST memory not equal to
configuration
Bit 3 = Fixed disk/adapter
initialization
0 = Initialization good
1 = Initialization failed
Bit 2 = CMOS time status indicator
0 = Time is valid
1 = Time is Invalid
Bits 1-0 = Reserved
0Fh 15 1 byte Shutdown code
00h = Power on or soft reset
01h = Memory size pass
02h = Memory test pass
03h = Memory test fail
04h = POST end; boot system
05h = JMP double word pointer with EOI
06h = Protected mode tests pass
07h = Protected mode tests fail
07h = Protected mode tests fail
08h = Memory size fail
09h = Int 15h block move
0Ah = JMP double word pointer without
EOI
0Bh = used by 80386
10h 16 1 byte Floppy disk drive types
Bits 7-4 = Drive 0 type
Bits 3-0 = Drive 1 type
0000 = None
0001 = 360K
0010 = 1.2M
0011 = 720K
0100 = 1.44M
11h 17 1 byte Reserved
12h 18 1 byte Hard disk types
Bits 7-4 = Hard disk 0 type (0-15)
Bits 3-0 = Hard disk 1 type (0-15)
13h 19 1 byte Reserved
14h 20 1 byte Installed equipment
Bits 7-6 = Number of floppy disk
drives
00 = 1 floppy disk drive
01 = 2 floppy disk drives
Bits 5-4 = Primary display
00 = Use display adapter BIOS
01 = CGA 40-column
10 = CGA 80-column
11 = Monochrome Display Adapter
Bits 3-2 = Reserved
Bit 1 = Math coprocessor present
Bit 0 = Floppy disk drive present
15h 21 1 byte Base memory low-order byte
16h 22 1 byte Base memory high-order byte
17h 23 1 byte Extended memory low-order byte
18h 24 1 byte Extended memory high-order byte
19h 25 1 byte Hard Disk 0 Extended Type (0-255)
1Ah 26 1 byte Hard Disk 1 Extended Type (0-255)
1Bh 27 9 bytes Reserved
2Eh 46 1 byte CMOS checksum high-order byte
2Fh 47 1 byte CMOS checksum low-order byte
30h 48 1 byte Actual extended memory low-order byte
31h 49 1 byte Actual extended memory high-order byte
32h 50 1 byte Date century in BCD
33h 51 1 byte POST information flag
Bit 7 = Top 128K base memory status
0 = Top 128K base memory not
installed
1 = Top 128K base memory installed
Bit 6 = Setup program flag
0 = Normal (default)
1 = Put out first user message
Bits 5-0 = Reserved
34h 52 2 bytes Reserved
4.16 shows the values that may be stored by your system BIOS in a