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

Adobe After Effects CC 2018 16.1.3 - Cre...
After Effects CC 2018 is available as part of Adobe Creative Cloud for $52.99/month (or $20.99/month for a single app license). The new, more connected After Effects CC 2018 can make the impossible... Read more
Adobe Audition CC 2019 12.1.4 - Professi...
Audition CC 2019 is available as part of Adobe Creative Cloud for as little as $20.99/month (or $9.99/month if you're a previous Audition customer). Adobe Audition CC 2019 empowers you to create and... Read more
Adobe Premiere Pro CC 2019 13.1.5 - Digi...
Premiere Pro CC 2019 is available as part of Adobe Creative Cloud for as little as $52.99/month. The price on display is a price for annual by-monthly plan for Adobe Premiere Pro only Adobe Premiere... Read more
Navicat Premium Essentials 12.1.25 - Pro...
Navicat Premium Essentials is a compact version of Navicat which provides basic and necessary features you will need to perform simple administration on a database. It supports the latest features... Read more
Sketch 58 - Design app for UX/UI for iOS...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more
ClipGrab 3.8.5 - Download videos from Yo...
ClipGrab is a free downloader and converter for YouTube, Vimeo, Facebook and many other online video sites. It converts downloaded videos to MPEG4, MP3 or other formats in just one easy step Version... Read more
Dash 4.6.6 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
FotoMagico 5.6.8 - Powerful slideshow cr...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Civilization VI 1.2.4 - Next iteration o...
Sid Meier’s Civilization VI is the next entry in the popular Civilization franchise. Originally created by legendary game designer Sid Meier, Civilization is a strategy game in which you attempt to... Read more
Skype 8.52.0.138 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more

Latest Forum Discussions

See All

Lots of premium games are going free (so...
You may have seen over the past couple weeks a that a bunch of premium games have suddenly become free. This isn’t a mistake, nor is it some last hurrah before Apple Arcade hits, and it’s important to know that these games aren’t actually becoming... | Read more »
Yoozoo Games launches Saint Seiya Awaken...
If you’re into your anime, you’ve probably seen or heard of Saint Seiya. Based on a shonen manga by Masami Kurumada, the series was massively popular in the 1980s – especially in its native Japan. Since then, it’s grown into a franchise of all... | Read more »
Five Nights at Freddy's AR: Special...
Five Nights at Freddy's AR: Special Delivery is a terrifying new nightmare from developer Illumix. Last week, FNAF fans were sent into a frenzy by a short teaser for what we now know to be Special Delivery. Those in the comments were quick to... | Read more »
Rush Rally 3's new live events are...
Last week, Rush Rally 3 got updated with live events, and it’s one of the best things to happen to racing games on mobile. Prior to this update, the game already had multiplayer, but live events are more convenient in the sense that it’s somewhat... | Read more »
Why your free-to-play racer sucks
It’s been this way for a while now, but playing Hot Wheels Infinite Loop really highlights a big issue with free-to-play mobile racing games: They suck. It doesn’t matter if you’re trying going for realism, cart racing, or arcade nonsense, they’re... | Read more »
Steam Link Spotlight - The Banner Saga 3
Steam Link Spotlight is a new feature where we take a look at PC games that play exceptionally well using the Steam Link app. Our last entry talked about Terry Cavanaugh’s incredible Dicey Dungeons. Read about how it’s a great mobile experience... | Read more »
Combo Quest (Games)
Combo Quest 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Combo Quest is an epic, time tap role-playing adventure. In this unique masterpiece, you are a knight on a heroic quest to retrieve... | Read more »
Hero Emblems (Games)
Hero Emblems 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ** 25% OFF for a limited time to celebrate the release ** ** Note for iPhone 6 user: If it doesn't run fullscreen on your device... | Read more »
Puzzle Blitz (Games)
Puzzle Blitz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Puzzle Blitz is a frantic puzzle solving race against the clock! Solve as many puzzles as you can, before time runs out! You have... | Read more »
Sky Patrol (Games)
Sky Patrol 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: 'Strategic Twist On The Classic Shooter Genre' - Indie Game Mag... | Read more »

Price Scanner via MacPrices.net

$250 prepaid Visa card with any Apple iPhone,...
Xfinity Mobile will include a free $250 prepaid Visa card with the purchase of any new iPhone, new line activation, and transfer of phone number to Xfinity Mobile. Offer is valid through October 27,... Read more
Sprint is offering the 64GB Apple iPhone 11 P...
Sprint has the new 64GB iPhone 11 Pro available for $12.50 per month for new customers with an eligible trade-in in of iPhone 7 or newer. That’s down from their standard monthly lease of $41.67. The... Read more
Final week: Apple’s 2019 Back to School Promo...
Purchase a new Mac using Apple’s Education discount, and take up to $400 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Save $30 on Apple’s AirPods at these reseller...
Amazon is offering discounts on new 2019 Apple AirPods ranging up to $30 off MSRP as part of their Labor Day sale. Shipping is free: – AirPods with Charging Case: $144.95 $15 off MSRP – AirPods with... Read more
Preorder your Apple Watch Series 5 today at A...
Amazon has Apple Watch Series 5 GPS models available for preorder and on sale today for $15 off Apple’s MSRP. Shipping is free and starts on September 20th: – 40mm Apple Watch Series 5 GPS: $384.99 $... Read more
21″ iMacs on sale for $100 off Apple’s MSRP,...
B&H Photo has new 21″ Apple iMacs on sale for $100 off MSRP with models available starting at $999. These are the same iMacs offered by Apple in their retail and online stores. Overnight shipping... Read more
2018 4 and 6-Core Mac minis on sale today for...
Apple resellers are offering new 2018 4-Core and 6-Core Mac minis for $100-$150 off MSRP for a limited time. B&H Photo has the new 2018 4-Core and 6-Core Mac minis on sale for up to $150 off... Read more
Save $150-$250 on 10.2″ WiFi + Cellular iPads...
Verizon is offering $150-$250 discounts on Apple’s new 10.2″ WiFi + Cellular iPad with service. Buy the iPad itself and save $150. Save $250 on the purchase of an iPad along with an iPhone. The fine... Read more
Apple continues to offer 13″ 2.3GHz Dual-Core...
Apple has Certified Refurbished 2017 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros available starting at $1019. An standard Apple one-year warranty is included with each model, outer cases are new... Read more
Apple restocks 2018 MacBook Airs, Certified R...
Apple has restocked Certified Refurbished 2018 13″ MacBook Airs starting at only $849. Each MacBook features a new outer case, comes with a standard Apple one-year warranty, and is shipped free. The... Read more

Jobs Board

Student Employment (Blue *Apple* Cafe) Spri...
Student Employment (Blue Apple Cafe) Spring 2019 Penn State University Campus/Location: Penn State Brandywine Campus City: Media, PA Date Announced: 12/20/2018 Date Read more
Geek Squad *Apple* Master Consultation Agen...
**732907BR** **Job Title:** Geek Squad Apple Master Consultation Agent **Job Category:** Services/Installation/Repair **Location Number:** 000360-Williston-Store Read more
*Apple* Mobile Master - Best Buy (United Sta...
**728519BR** **Job Title:** Apple Mobile Master **Job Category:** Store Associates **Location Number:** 000853-Jackson-Store **Job Description:** **What does a Best Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**733006BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Location Number:** 000865-Conroe-Store **Job Description:** At Best Buy, our Read more
*Apple* Mobility Pro-Store 149 - Best Buy (U...
**731985BR** **Job Title:** Apple Mobility Pro-Store 149 **Job Category:** Store Associates **Location Number:** 000149-Towson-Store **Job Description:** At Best Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.