Secrets Home Page
Prediction in the Pentium Family by Agner Fog
This article describes how the branch prediction mechanism in the Pentium has been uncovered with all its quirks, and the incredibly more effective branch prediction in the later microprocessor versions.
PC Processors Explained By Robert R. Collins
Welcome Computalk readers.
This article was prepared Tom King at Computalk.COM. This brief article provides an overview of the various generations of x86 microprocessors.
Chipsets: The Most important components in a computer system by Billy Newsom
(Following this link will take you away from this web site.)
Have you ever wondered how much difference a chipset makes in the performance of your computer system? This definitive article was submitted by one of my readers. Billy offered, and took it upon himself to write this excellent, and thorough article about computer chipsets, and their relationship to the performance of your computer system.
Sizing Memory In Protected Mode by Robert R. Collins
Have you ever wondered how
the BIOS sizes memory? If you have, then you'll want to
take a look at this article. In this article, I discuss
the basic method which the BIOS uses to determine how
many banks of memory, and the size of each DRAM chips.
Protected Mode Virtual Interrupts on the Pentium and SL-Enhanced i486 Intel Processors by Maciej W. Rozycki
This article discloses the last
piece of Appendix H information which has not already
been disclosed at this web page. Protected Mode Virtual
Interrupts (PVI) is supposed to be the protected mode
counterpart to VME (Virtual Mode Enhancements, discussed
below). However well intentioned Intel was in providing
this feature, it's still rather brain-dead and doesn't
solve the problem caused by POPF (or IRET) when the
EFLAGS image of the interrupt flag needs to be changed.
Regardless of the limitations of PVI, this article is
invaluable for understanding this secret Pentium
feature. The article comes complete with source code and
a downloadable executable to demonstrate this feature.
Page Size Extensions on the Pentium Processor by Robert Collins
In order to receive information
from Intel regarding the Pentium's 4 MB Page Size
Extensions, Intel required you to sign a 15-year NDA. But
little did you know that for the past three years, this
information has been publicly documented in the Intel
i860 XP manual. How ironic!
Virtual Mode Extensions on the Pentium Processor by Robert Collins and Jim Brooks
It has taken over four years for
this information to be liberated from Appendix H. The
people who knew it, couldn't talk about it. Those who
didn't know it, wanted it. Now it is finally here: all of
the details of the Virtual Mode Extensions on the Pentium
Processor. Abundant source code examples are provided as
Paging Extensions for the Pentium Pro Processor by Robert Collins
Most people never knew that the
Pentium Processor was going to implement 36-bit
addressing, and 2-Mbyte pages. As far as I know, these
features were implemented in beta silicon, but scrapped
for production. Well, they're back on the Pentium Pro
Processor, with some other page mode extensions.
Pentium Model-Specific Registers and What They Reveal by Ralf Brown
This is an excellent article by
Ralf Brown, the author of the Interrupt List.
In this article, Ralf unlocks the secrets to hidden
model-specific registers on the Pentium processor and
discloses what they contain.
An Overview of Pentium Probe Mode by Robert Collins
This article gives a brief overview
of how the Pentium Probe Mode works. What is probe mode
used for? How does it work? How does it interface with
the Pentium? How do you enter and exit probe mode? All of
these topics are discussed in this article.
The Probe Mode Control Register by Robert Collins
The Probe Mode Control Register
(PMCR) is also known as the Debug Mode Control Register
(DMCR). Many people have seen the DMCR listed in Pentium
books, but were never told how to access it. This article
not only discloses how to access it, but how to use it to
The LOADALL Instruction by Robert Collins
Magazine article by the illustrious
Robert Collins (me) in the October 1991 issue of Tech
Specialist. In the Annotated Bibliography of
Andrew Schulman's book, Undocumented DOS, Second Edition,
Andrew says of this article "Collins uses an
in-circuit emulator (ICE) to take apart the undocumented
LOADALL instruction; an amazingly good article."
Thank you Andrew, I think the same of your book.
Protected Mode Basics by Robert Collins
This is an unpublished magazine article I wrote in 1991. I had originally intended to submit it for publication in Tech Specialist, but I eventually lost interest. As I converted the article to hypertext, I was amazed at how informative I had written it (that many years ago). And with my current understanding of the x86 architecture, I detected only one mistake in the article (which I corrected). If you have a desire to know more about protected mode, or learn protected mode basics, then you should read this article. It comes complete with source code, which can be downloaded.
The Story of the CISC King and Appendix H by Robert Collins
This biblical parody chronicals the
history of the Intel x86 processors, the creation of
Appendix H, and its liberation by a host of shady
characters, including, yours truly. The story is not
meant to be offensive, though my wife was furious when
she read it.