TweetFollow Us on Twitter

May 96 Viewpoint
Volume Number:12
Issue Number:5
Column Tag:Viewpoint

Viewpoint

By Scott T Boyd, Editor Emeritus, http://www.montara.com/

Way back in 1984 Apple did something fundamentally different with the Macintosh that few people talk about when singing Apple’s praises for changing computing’s paradigm.

We came to know it as the A-trap mechanism. For those who haven’t delved into this before, it’s a little oddity made possible by Motorola’s chip designers. Many people might not have even noticed a feature which captured the imagination of a few special people at Apple. 68xxx processors have a number of instructions or conditions which generate exceptions. Each of these causes an exception handler to get called. One entire class of exceptions is triggered by any instruction whose hex value begins with an $A (e.g. $ABCD, $AAFA, etc ). Those wise guys at Apple figured out that they could have the A-line exception code use the instruction’s value as something of an index to figure out which function to further dispatch to. This we now know as the A-trap dispatcher.

The greatest disadvantage of this approach was execution time. It takes time to “throw” an exception. The processor has to put a fair amount of its state onto the stack before it can jump to the exception vector (and restore it later). Then the dispatcher has to do some fancy footwork to figure out who to call, and sometimes it saves and restores even more registers.

Now for the upside. First, a two byte trap word is smaller than any jump you could hope to make into a library of functions. On a 128K machine, that kind of savings really added up. Second, it made it easy to conceive of a vast library of functions that any code could call. While A-traps weren’t necessary for things like the Macintosh Toolbox, they sure didn’t hurt. They provided a consistent mechanism to dispatch to code anywhere on the machine, be it in the ROM, in RAM, or even on the disk, using a standard lookup key (the trap word). Third, it created a mechanism whereby Apple engineers and third parties could correct, modify, and extend the vast library of code (we know this as patching and/or implementing traps).

For years Macintosh programmers felt special. A-traps offered a rich breeding ground for unusual software. We customized our machines in ways not even imaginable on other (lesser?) machines. We had more fun and productivity to show for it, as well as a thriving utility software market.

Alas, the A-trap mechanism might very well have been too useful. You see, there came a time with other operating systems started to face some of the problems that Macintosh had already confronted. Only by this time these machines were already an order of magnitude larger. Perhaps their OS engineers weren’t as clever as Apple’s, but they didn’t seem particularly interested in paying the price of exception handling to do a late-binding method dispatch (which is, after all, essentially what we’ve been talking about). While Apple was busily guarding and carefully managing the growth of the trap tables, other OS vendors were coming up with these things called DLLs - Dynamically Linked Libraries.

DLLs are like object code libraries, but aren’t linked directly into an application, and can generally be shared. In that sense, they can become like system software, with just one copy of a library per machine. If you put some system functionality into a DLL, you can often ship it by itself rather than wait for an entire system release. Apple has long achieved this effect by shipping extensions which, when installed, add new functionality at boot time. DLLs have the benefit, though, of not needing to load at boot time, and not having to live in a special place on disk. DLLs also have the benefit of freedom from the space constraints that trap code typically tries to live by. With the addition of file mapping and a good virtual memory system, they can even execute directly off of disk. Have a good night programming and speed up a DLL by 50%? Ship the new DLL and watch all of the apps which use it simply go faster! Other operating systems mastered this before Apple even realized that having a DLL mechanism would be a good thing to have.

Apple dabbled with ASLM, the Component Manager, and others. Fortunately, the PowerPC effort brought forth the Code Fragment Manager, the one we’ve been waiting for, and now 68K CFM is ready, too. I’ve recently been involved in an effort to build some fat code fragments for use by a dynamic language environment, and I’ve got to tell you that I am pumped!

But now I find that I want lots more fragments to play with. Wouldn’t you like to have a DLL that converted PICTs to GIF, told your Web browser to resolve a URL, or went a ftp’d a file, all with the ease of a couple of function calls? Here’s where you come in. You know that really clever or useful library you wrote and linked in to your latest application? How about that slick little shareware utility? How about releasing it as a DLL? That and a header file, and you can have thousands of grateful developers treat you like their own system software engineer. CFM is cool. If you learn just one new thing today, learn what CFM can do for you. One starting point is :

http://dev.info.apple.com/evangelism/DLLDirectional.html

I also recommend looking at Apple’s latest Developer CDs.

Food for Thought

Presenting his keynote to the Microsoft Professional Developers Conference, Bill Gates noted that he believes that the #1 reason to develop for Windows is “Volume!” That’s 60 million copies of Windows each year. As an aside, he mentioned, “30 million copies wouldn’t pay Microsoft’s bills.”

 
AAPL
$99.18
Apple Inc.
-1.57
MSFT
$45.90
Microsoft Corpora
-0.46
GOOG
$568.27
Google Inc.
-9.09

MacTech Search:
Community Search:

Software Updates via MacUpdate

Cocktail Family License (5 Macs) 7.6.1 -...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cocktail 8.0 Beta 2 - General maintenanc...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
QuickBooks 2015 16.0.0.1352 R1 - Financi...
QuickBooks 2015 helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save.... Read more
Mac DVDRipper Pro 5.0.1 - Copy, backup,...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
Apple OS X bash Update 1.0 - Fix for sec...
The OS X bash Update fixes a security flaw in the bash UNIX shell on OS X 10.9.5 (also on OS X 10.8 and 10.7 [see Related Links below]). OS X 10.9.5 or later Downloads for OS X 10.8 and OS X 10.7 in... Read more
SyncTwoFolders 2.0.5 - Syncs two user-sp...
SyncTwoFolders simply synchronizes two folders. It supports synchronization across mounted network drives and it is a possibility to run a simulation showing in a log what will be done. Please visit... Read more
FinderPop 2.5.7 - Classic Mac utility, n...
FinderPop is a Universal preference pane that extends OS X's contextual menus using a FinderPop Items folder much as the Apple Menu Items folder used to do for the Apple menu. It has other features... Read more
VueScan 9.4.45 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
LibreOffice 4.3.2.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
calibre 2.4 - Complete e-library managem...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more

Latest Forum Discussions

See All

Banner Saga (Games)
Banner Saga 1.0.17 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.17 (iTunes) Description: NOTE: The Banner Saga does NOT run on iPhone 4. iPhone 4S and more modern devices recommended. | Read more »
Beatbuddy HD (Games)
Beatbuddy HD 1.0.2 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.2 (iTunes) Description: **IMPORTANT** Beatbuddy runs only on iPhone 6, 6 Plus, 5, 5c, 5s, iPad 4, iPad Mini Retina and iPad Air. | Read more »
iKeywi - Customizable 5-Row Keyboard (U...
iKeywi - Customizable 5-Row Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $.99, Version: 1.0 (iTunes) Description: Want to add an extra row to your iPhone/iPad? One of the most popular keyboard extension in iOS... | Read more »
Manage Your Cloud – Wunderlist Now Suppo...
Manage Your Cloud – Wunderlist Now Supports Dropbox Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Nexticy Review
Nexticy Review By Jennifer Allen on October 1st, 2014 Our Rating: :: IDEAL FORM CREATIONiPad Only App - Designed for the iPad Nexticy allows you to make your own forms for research purposes or to organize your business better. It’s... | Read more »
Tiny Troopers: Alliance Marches onto the...
Tiny Troopers: Alliance Marches onto the App Store Tomorrow Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Tiny Troopers: Alliance, by Kukouri, is a | Read more »
HeroCraft Introduces Unlimited Sequel to...
HeroCraft Introduces Unlimited Sequel to WW2: Sandbox. Strategy & Tactics Posted by Jessica Fisher on October 1st, 2014 [ permalink ] | Read more »
RGB Express Review
RGB Express Review By Jennifer Allen on October 1st, 2014 Our Rating: :: DELIGHTFUL PUZZLINGUniversal App - Designed for iPhone and iPad Guide trucks along their delivery routes in RGB Express, a testing but charming puzzle game... | Read more »
The Sagas of Fire*Wolf (Games)
The Sagas of Fire*Wolf 1.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0 (iTunes) Description: | Read more »
BuggyFun Review
BuggyFun Review By Amy Solomon on October 1st, 2014 Our Rating: iPad Only App - Designed for the iPad BuggyFun allows children to create their own tracks for bugs to interact with for a unique open-ended experience.   | Read more »

Price Scanner via MacPrices.net

ASUS, Lenovo, and Amazon Slug It Out For Tabl...
According to market intelligence firm ABI Research, Apple and Samsung have led the touchscreen tablet market by a substantial margin since Apple energized the category back in 2010. However, ABI says... Read more
Amazon offers 13-inch MacBook Air for $899, $...
Amazon.com has the 13″ 1.4GHz 128GB MacBook Air on sale for $100 off MSRP including free shipping: - 13″ 1.4GHz 128GB MacBook Air: $899.99 Read more
Apple resting On Its iPhone Laurels? – The ‘B...
Apple calls its new iPhone 6 and 6 Plus “The Biggest Advancements in iPhone History,” but does reality live up to the hype? “Seldom have so many waited so breathlessly for so little,” tweeted veteran... Read more
Roundup of Apple Mac and iPad Education disco...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Apple Boycotts German Magazine Computer Bild...
Apple has revoked its PR accreditation of Germany’s Computer Bild, Europe’s best-selling PC magazine, in reaction to Bild’s posting of a “#Bentgate” YouTube video. Axel Telzerow, editor in chief of... Read more
iPhone 6 & iPhone 6 Plus Available in Chi...
Apple has announced that iPhone 6 and iPhone 6 Plus will be available in China beginning Friday, October 17 from the Apple Online Store (http://www.apple.com), Apple’s retail stores, and an expansive... Read more
MacBook Airs on sale for $100 off MSRP, start...
Best Buy has the new 2014 MacBook Airs on sale for $100 off MSRP on their online store. Choose free home shipping or free local store pickup (if available). Prices valid for online orders only, in-... Read more
Apple Releases OS X Mavericks bash Update 1.0...
Apple has released a patch update for OS X Mavericks users to address the recently-detected “Shellshock” security bug in BSD UNIX’s bash shell. Apple says only a few Mac users who had manually... Read more
Pivotal Payments Ready for Apple Pay – FlexPo...
Pivotal Payments, a provider of merchant services and global payment processing solutions, has announced its proprietary FlexPoint platform will support credit and debit transactions through Apple’s... Read more
iStabilizer Announces Tabarm — First Friction...
iStabilizer, a specialist in universal lightweight compact tripods, steady cams, dollies, mounts, and remotes for smartphones, tablets, and cameras, announced today the iStabilizer tabArm, the first... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.