The Secrets of Mental Math

I’ve read more than a few books on mental arithmetic, and have found some that I like. Strangely enough, they are not common in libraries, despite the fact that one of them is written by an author virtually every one will recognize instantly.

I’ve been reading most recently Secrets of Mental Math by Arthur Benjamin and Michael Shermer. Arthur Benjamin recently gave a keynote speech at a national tech event (was it OSCON?). I wanted to see his book and what he had to offer that I hadn’t read recently. I didn’t like it as much as I thought - more of the book was dedicated to “tricks” (to amaze your friends!) than I would have liked. Most books of this sort focus on making daily calculations much easier. I also found his writing to be not as clear as the others I have read on this topic.

One interesting item put into Secrets of Mental Math is the method of finding the day of the week for any future year. This topic is also considered in The Memory Book by Harry Lorayne and Jerry Lucas, but in The Memory Book the method is to memorize a number representing the days that Monday falls on throughout the year (that is, a 12-digit number). Secrets of Mental Math proposes a mathematical formula, utilizing a code number for the month and a code number for the year. The code number for the month (and for the year) is never completely explained, but would probably be based on the day of the week that the month will have given that the year starts on Monday (or something like that) - plus a shift factor coded into the year code.

So your choice - choose the memorization method in The Memory Book or the calculation method found in Secrets of Mental Math. Of course, the latter handles every date in every year without memorization - but people would rarely use such a method for anything other than the current year, most likely.

The book I have in my collection that I prefer in this area is Calculator’s Cunning by Karl Menninger, translated from German by E. J. F. Primrose (with foreward by Martin Gardner). I am surprised that this book is not more widely available; it appears to be out of print. Karl’s writing (and Primrose’s translation) is very easy to read, understandable, and clear - and mathematical proofs are offered at the end of each section where the trick is introduced.

Another which is almost as hard to find in the library as the tome by Karl Menninger is a book by the venerable Isaac Asimov titled Quick and Easy Maths. This book may or may not be available at your local library, but chances are good you’ll have to go to interlibrary loan to get it, or even buy used. The book is out of print, just as Calculator’s Cunning is. Asimov is one of the clearest writers I’ve seen, and Quick and Easy Maths is no exception.

Also, the methods described in all three mental mathematical books are essentially the same - even so, the experience of reading of all three is all worthwhile.

Then next time you have to calculate the number of hosts in a subnet, you’ll be able to do it in your head - or adding up an invoice!

Tips on Improving Your Public Speaking

Every system administrator should hone their public speaking skills for those times when you have to present your projects to the higher ups or train the staff on the new software.

Today, there are a variety of excellent sources of how to improve your public speaking - several from Guy Kawasaki. Guy has some tips that he received from his buddy Doug Lawrence. One he titled “Speaking as a Performing Art“, and a week later “Bite Your Tongue: Eight More Ways to Improve Your Presentations“.

Some tips that stood out to me (not in any particular order) are:

Don’t overwhelm the audience. Be entertaining but use moments of silence, soft speech, and slow cadence.

Skip the tea. Tea is an astringent and will close your voice down.

Use your eyes all the time. Hand gestures, pacing around the platform can all be useful tools in presentation, but the eyes…ah, the eyes have it!

Move away from center to make your point. When you come to a place in your presentation where you really want people’s attention, move to the left or right of your primary speaking position.

If those 15+8 tips from Guy Kawasaki weren’t enough, from Ian’s Messy Desk, Ian McKenzie has 10 ways to improve your public speaking.

As always, the ultimate place to practice public speaking is with your local Toastmasters organization. Why not join today?

Encrypting and Hiding a Windows Partition

Over at Textual Relations, Adam Heckler has a good description on how to encrypt and hide a Windows partition. Though it accomplishes its task (and well!) it will not be hidden from most technologically aware individuals, and the encryption key can be subponaed by the court (if that would be of concern to you). However, if all you want to do is to encrypt files and hide them from the usual prying eyes, it may be just fine.

The steps (concisely put) are these:

• Shrink the current Windows partition
• Create a new partition (to store files)
• Create a new encyrpted filesystem (using TrueCrypt) on the new partition
• Unmount the disk using the standard Windows tools

As you can see, the “hiding” of the partition is merely unmounting it - but it will not be visible to anyone unless they go looking for it. For protection against most normal users, that would be fine. The disk will not show up in My Computer though it may show up in listboxes for mounting disks and other such things - this would bear investigation.

As an aside - you might want to see Adam’s usage chart after Lifehacker posted about his instructions. Wow!

Imaging a System with Open Source Software

With the use of the System Rescue CD, gParted, and Partimage, it is possible to take an image of a system partition and to save it to another partition (for restoration or other purposes). Lifehacker had a complete description of how to do this (with screenshots); if you’re a system administrator, most of the steps should almost be self-explanatory (almost). The basic steps are these:

• Resize the partition
• Create a partition to store the image
• Image the disk to a disk file on the secondary partition

There must, of course, be enough space on the secondary partition to store the image. Generally, since the image is a pristine environment, it should compress to a smaller size than the partition it is on. For example, a new Windows install on a 20G drive will not`certainly take 20G.

What the System Rescue CD does is make this much easier and place all of the programs together, and in a graphical form. The Rescue CD also contains network tools and other programs. The Rescue CD may be copied to a USB memory device and run from there if you have a system that will boot from a USB stick.

Although there is also a PowerPC version, it appears to be a version from 2003 which has not seen significant development since. Perhaps I will dip my fingers into it - I’ve wanted to get back into development again.

The System Rescue CD is also suitable for a small CDROM - that is, it is less than 150M in size. This can be quite handy, and means that a 256M USB memory device is just the right size - and that the download is not going to be huge. There are instructions on how to make your own customized CD, as well as instructions on how to create a bootable USB stick with the CD.

A Quickie: A PDF of all Macintosh OS X Key Shortcuts!

There is a list of all available Macintosh OS X key shortcuts in a PDF (or three). This includes foreign characters, mathematical symbols, and more. So if you want to write en français, you can - or enjoy writing about a delicious éclair - or about that new hôtel de Paris - you can. You can écrit des articles en français et discut les ordinateurs toute les jours!

(Okay, so I speak - or try to speak - French. I believe that I already wrote about using foreign languages….)

Supporting the Marvell Libertas 8335 Under FreeBSD

If you’ve been following along, I’ve been trying many operating systems on my Compaq Armada E500. The hardware has been preforming superbly, and does not have any problems except that everything current seems to think that 128M of memory is a pittance. FreeBSD 6.2, however, did install.

The biggest problems have been wireless and USB support. Since my USB port disintegrated (it split in two, the plastic key came out, and the pins bent!) I’ve been limited to Cardbus cards. The system came with a Zonet 1502 which I mistakenly thought used a Realtek chipset like the Zonet 1500 and 1501 (the FreeBSD ral(4) driver).

I used ndisgen(8) to create a kernel module based on the Windows driver. This went flawlessly, and the module loaded perfectly - recognizing the card immediately:

cardbus1: Resource not specified in CIS: id=14, size=10000
ndis0: <Marvell Libertas 802.11b/g Wireless (8335)> mem 0×88000000-0×8800ffff,0x
88010000-0×8801ffff irq 11 at device 0.0 on cardbus1
ndis0: NDIS API version: 5.0
ndis0: Ethernet address: 08:10:74:05:11:8f

The device, however, never seems to turn on - the power light never lights - and thus, the link light never activates. It would appear I can modify at least some of the parameters but not others - such as the channel. The power light never comes on whatever I might do.

Pulling the card and reinserting generates an error for some reason.

Investigating this card turns up the fact that it is supported under OpenBSD, and that the chipset is known for being closed. This article discusses the author’s experiences with the Netgear WG511 v2 (perhaps one of the most common cards containing the Marvell Libertas chipset) and his OpenBSD system with Kismet. The OpenBSD folks use the malo(4) driver to control such a beast, the word malo having some interesting Spanish meanings.

In a 2007 slide presentation titled “Open Documentation for Hardware” about the state of open source hardware documentation, Theo de Raadt stated that “Marvell is being dragged open kicking and screaming“. He also noted that “No other operating system has as many 802.11 drivers builtin“.

There is some discussion about using the Netgear WG511 v2 with Linux, again using the Windows NDIS drivers.

The FreeBSD Handbook was useful in investigating this generic ndis0 wireless card configuration; specifically, Section 11.8.1.1 on setting up a network card using a Windows NDIS driver, and Section 29.3 on wireless networking.

Wikipedia has an article that compares open source wireless drivers which has proved to be quite informative; if this Zonet card does not work, I may use this article to help choose another card.

With the advent of this research, if FreeBSD doesn’t work out, I’ll probably go to OpenBSD after imaging the disk.

Expanding your desktop across operating systems

When you use Synergy, it connects one computer (and desktop) to another. Your mouse will flow seamlessly from one desktop to the next. A number of desktops can be combined, although programs remain confined to their desktops.

Synergy is different from multiscreen desktops - a standard multiscreen desktop stretches a single operating system environment across multiple screens or displays. In most normal cases, this is what would be preferred for normal users. However, if you are using multiple systems for different purposes, you can concatenate separate displays together.

When you move your mouse from one desktop (Mac OS X, for instance) to another, it is like moving from one computer to the next. In some ways, it is like a multi-screen software KVM (Keyboard-Video-Mouse) switch. The server runs on the system with the keyboard and mouse, and the clients run on other systems. Each system has its own monitor, and can be placed (virtually) anywhere through proper configuration of the server. For example, the screens could be placed one on top of the other, or side by side. If one display is disconnected, then it will be skipped. For example, if there are three screens in a row, and the middle one loses connection to the server, then it will be skipped over as the mouse moves from one system to the other.

Recently, I had the server running on Mac OS X, a client on Fedora Core 5, and a client under Solaris 8. The mouse could then be moved to the left side of the Mac OS X display, and it would appear on the right on the Fedora Core 5 display. Continuing to move the mouse, it would eventually wind up on the Solaris 8 display. The only drawbacks are the network delay and differing mouse speeds. I’ve grown addicted to it - try it today!

Wireless support for Linux and FreeBSD

In my quest to test out my Compaq Armada E500, it turns out that the hardest thing to support are the two wireless devices I have to work with it. One is a Linksys USB device with a ZyDAS 1211 chipset. I found an open source driver project (zydas1211rw) providing Linux support for this ZyDAS chipset. This driver has been included in the Linux kernel since version 2..6.18. However, the zyd(4) driver for FreeBSD is still in the development stage. Apparently OpenBSD and NetBSD already support this chipset (as that is the origin of the driver).

The other device I have is a Zonet ZEW1502. This device seems to be largely unknown, though folks have been able to get the Ralink drivers to work with it. However, none of the directories of Ralink devices mention it (though they do mention the ZEW1500 and ZEW1501). Unfortunately, the Ralink drivers ral(4) and ural(4) only show up in FreeBSD 6 as best as I can tell.

I went with FreeBSD 6 on the laptop, and it works just fine. I’ve not tried GNOME or KDE, but WindowMaker and 9wm work quite ably. 9term was mostly a pain, but xterm works (of course it does). However, the hoped-for ral(4) driver doesn’t work with the Zonet ZEW1502. The system recognizes a Cardbus device has been inserted, but that’s all.

Now that the USB adapter is shot, the Cardbus/PCMCIA is all I have. The USB plug broke apart and subsequently came undone. It was in a part of the computer that already had its case broken off, so it had no protection anyway. Sigh. That’s the *only* time this hardware has actually let me down. Time to focus on the Zonet - or to replace it.

What’s Your Favorite Operating System?

I was asked this question recently. Everyone likely has an answer: Red Hat Linux, Debian GNU/Linux, Solaris… My answer surprised the questioner: UNIX and UNIX-workalikes. This includes FreeBSD… and Red Hat… and Solaris… and HP-UX… and AIX… and so forth. When I first became interested in UNIX, not one of the aforementioned products existed. First UNIX system I got my hands on briefly was Eunice (look it up and the next (a few years later) was Microport System V (for the IBM AT).

Perhaps you might think Solaris is better than Linux - or NetBSD is better than OpenBSD. I suggest it doesn’t matter. Each UNIX (or UNIX-like) environment has its pluses and minuses. Individual choices are personal and enterprise choices are practical - in either case, which is truly better doesn’t matter.

If your enterprise is using Oracle, for example, the choice of which UNIX system you use is dramatically reduced: which system will Oracle support? You won’t be using Oracle on FreeBSD unless you forgo the Oracle maintenance contract. Choices like this continually appear in the enterprise. Perhaps the new version of Red Hat Enterprise Linux has everything you want - but Oracle doesn’t yet support that version.

Alternately, which system you use for your own desktop is a personal choice. Which one is “better” is which one feels better to you. UNIX is, at its heart, unified - that is, it is a single environment - but it provides a wide choice of user interfaces, user programs, and even technical items such as filesystems and virtual memory management schemes. Use whichever one seems better.

What do I use on my personal desktop? Mac OS X. However, in line with the ideas posited above, I’ve just expanded my “desktop” with Synergy, linking my “other” desktop (first Fedora Core 5, now BeleniX with OpenSolaris core) to my Mac OS X desktop. More about Synergy later.

So next time someone tells you what their favorite operating environment is - why not find out what it is they’re so excited about? You might find something exciting yourself.

The decTop $100 Computer!

Lifehacker has an article on a product called the decTop. It is billed as a Internet-browsing appliance, but is apparently a complete (and upgradable) computer as well. Sounds like the perfect hacker computer.

It does seem to be slowish by modern standards, and if my experience with 128M is any indication, it won’t run the most current distributions. There are some excellent discussions on how to install Ubuntu 6.06 onto it: one from Jonathon Scott and one from Ray over at Librenix. Juan Romero Pardines from the NetBSD Project has put NetBSD onto the decTop. Someone else put AstLinux onto a decTop - and added great pictures of the internals as well.

Over at Docunext there is a great series on the decTop, including pictures of the guts and of the locked drive (apparently no longer locked in current versions). There is also a set of tips on getting Debian to work on the decTop, as well as the author’s experiences in running the decTop on solar power.

The system advertises an ethernet connection, but it is, in fact, an USB-ethernet dongle. This fact combined with the USB-1.1 means that the ethernet connection is very, very slow. Everything hooks into the USB ports, including keyboard and mouse as well as the Ethernet connection. These two facts appear to be some of the worst drawbacks of the device.

There also appears to be no wireless support at all - the Internet browsing devices I’ve seen all use wireless connectivity as their main connection method - so this appears to be more of a desktop device, rather than a portable device. It is fanless, which means near absolute quiet. Who knows, maybe they’d make a good cluster (heh).

I must admit, when I first heard the name, I thought it might be a minature of one of these instead. Silly me.