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.”

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

5 slither.io mash-ups we'd love to...
If there's one thing that slither.io has proved, it's that the addictive gameplay of Agar.io can be transplanted onto basically anything and it will still be good fun. It wouldn't be surprising if we saw other developers jumping on the bandwagon,... | Read more »
How to navigate the terrain in Sky Charm...
Sky Charms is a whimsical match-'em up adventure that uses creative level design to really ramp up the difficulty. [Read more] | Read more »
Victorious Knight (Games)
Victorious Knight 1.3 Device: iOS Universal Category: Games Price: $1.99, Version: 1.3 (iTunes) Description: New challenges awaits you! Experience fresh RPG experience with a unique combat mechanic, packed with high quality 3D... | Read more »
Agent Gumball - Roguelike Spy Game (Gam...
Agent Gumball - Roguelike Spy Game 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Someone’s been spying on Gumball. What the what?! Two can play at that game! GO UNDERCOVERSneak past enemy... | Read more »
Runaway Toad (Games)
Runaway Toad 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: It ain’t easy bein’ green! Tap, hold, and swipe to help Toad hop to safety in this gorgeous new action game from the creators of... | Read more »
PsyCard (Games)
PsyCard 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: From the makers och Card City Nights, Progress To 100 and Ittle Dew PSYCARD is a minesweeper-like game set in a cozy cyberpunk... | Read more »
Sago Mini Robot Party (Education)
Sago Mini Robot Party 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: -- Children's Technology Review Editor's Choice -- | Read more »
How to get a high score in every level o...
Sky Charms is an adorable match three puzzler that provides a decent challenge thanks to its creative level design. It regularly presents something new, forcing you to think on your feet. [Read more] | Read more »
Apestorm: Full Bananas (Games)
Apestorm: Full Bananas 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: ***Launch sale – limited time only!*** Fugitive Apes have taken to the skies in search of revenge after humans have... | Read more »
How to create bigger words in Spellspire
Words have power. At least they do in Spellspire,a game about blasting out magical attacks by making words out of a jumble of letters. And it's a lot of fun. But if you want to be the best, you're going to have to think tactically when you start... | Read more »

Price Scanner via MacPrices.net

15-inch 2.2GHz Retina MacBook Pro on sale for...
Amazon.com has the 15″ 2.2GHz Retina MacBook Pro on sale for $1699.99 including free shipping. Their price is $300 off MSRP, and it’s the lowest price available for this model from any reseller (and... Read more
Apple Beats Microsoft at Own Game; Amazon Pri...
First quarter seasonality combined with an overall disinterested customer base led to an annual decline of 14.7% in worldwide tablet shipments during the first quarter of 2016 (1Q16). Worldwide... Read more
Aleratec Releases Mac Software Upgrade for 1...
California based Aleratec Inc., designer, developer and manufacturer of Portable Device Management (PDM) charge/sync products for mobile devices and professional-grade duplicators for hard disk... Read more
Sale! Amazon offers 27-inch iMac, 13-inch 2.9...
Amazon has the 27″ 3.2GHz 5K iMac and the 13″ 3.9GHz Retina MacBook Pro on sale for $300 off MSRP, each including free shipping, for a limited time: - 27″ 3.2GHz/1TB HD 5K iMac (model MK462LL/A): $... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
13-inch 2.7GHz/128GB Retina MacBook Pro on sa...
Take $200 off MSRP on the price of a new 13″ 2.7GHz/128GB Retina MacBook Pro (model MF839LL/A) at Amazon. Shipping is free: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1099.99 $200 off MSRP Act now if... Read more
Apple refurbished clearance 15-inch Retina Ma...
Apple has Certified Refurbished 2014 15″ 2.2GHz Retina MacBook Pros available for $1609, $390 off original MSRP. Apple’s one-year warranty is included, and shipping is free. They have refurbished 15... Read more
27-inch 5K iMacs on sale for up to $150 off M...
B&H Photo has 27″ 5K iMacs on sale for up to $150 off MSRP including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1849.99 $150... Read more
What Does The Refreshed 12-Inch MacBook Tell...
A lot of commentators are complaining that Apple’s update of the 12-Inch MacBook last week is a bit of a damp squib. I don’t know what they were expecting, since it would be very unlike Apple to do a... Read more
Free Wittify Keyboard Now Available On The Ap...
A team of Harvard Business School students have announced that the Wittify Keyboard, a new app utility for iOS devices, is now available on the Apple App Store. The Wittify keyboard and application... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 48260200 Phoenix, Arizona, United States Posted: Apr. 22, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Solutions Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.