The Road Ahead: 64-Bit Computing
Apple is billing Mac OS X 10.6 "Snow Leopard" as its first fully 64-bit operating system, but this isn't the first time the Mac OS has changed it bitness.
The world of personal computing began with 8-bit CPUs that could support up to 64 KB of memory. It seemed like a lot at the time, as many early PCs (back when that stood for Personal Computers) only shipped with 4 KB, 8 KB, or perhaps 16 KB of RAM.
The biggest technological breakthrough in the 8-bit era was bank switching, which allowed a CPU to switch between two or more 64 KB banks of memory. The most popular 8-bit operating system was CP/M.
Although the IBM PC was the machine that marked the shift from 8-bit to 16-bit computing, it wasn't the first 16-bit PC. That honor goes to the Texas Instruments TI-99/4, which was released in June 1979. It was overpriced for the home computer market, as it shipped with a 13" Zenith color monitor. It used a chiclet keyboard, had a cartridge slot for games and programs, and used a costly expansion chassis if you wanted to add drives. Like early Apple II computers, it didn't even have lower case.
The 3 MHz 16-bit CPU only had access to 256 Bytes of 16-bit memory - everything else was on an 8-bit bus and handled by a multiplexer. This is because TI had intended to ship an 8-bit PC, but the 8-bit CPU it was designing for the machine was abandoned. This was far from the last time the PC world would see such an architecture.
The most popular 16-bit CPU on an 8-bit bus was the Intel 8088 used in the original IBM PC, its early successors, and a glut of IBM clones. Intel had designed the 8086 as a 16-bit CPU with a 16-bit bus, and it could address up to 1 MB of memory in 64 KB banks. The 8088 allowed computer makers to use a less expensive 8-bit memory bus. Lower costs mean lower prices. So what if performance suffered a bit.
MS-DOS, Microsoft's adaptation of CP/M, was the most popular 16-bit operating system.
The 24-bit Mac OS
Although the Macintosh Team had originally hoped to use the Motorola 6809 8-bit CPU to keep costs down, the decision to go with a relatively high resolution graphical user interface (GUI) required more power. Apple chose the Motorola 68000 CPU as the heart of the original Macintosh, the same chip the Lisa team had settled on for its $10,000 machine.
The 68000 was a 32-bit CPU on a 16-bit bus with a 23-bit address bus that could handle up to 16 MB of RAM. Although it had a 32-bit architecture, it ignored the high-order byte and functioned as a 24-bit CPU. The Mac's ROMs and operating system were all created for this 24-bit environment with a maximum 16 MB address space.
That wasn't a limitation in the early Mac era - 512 KB was viewed as a lot of memory after the 128 KB Mac, and the Mac Plus could be expanded from a mind-boggling (for 1986) 1 MB of RAM to 4 MB - if you could afford it. It wasn't until the 1987 introduction of the Mac II that any Mac had a true 32-bit CPU or could handle more than 4 MB of RAM. As high capacity chips weren't yet available, the 128 MB theoretical maximum sounded very future oriented, but the early Mac OS couldn't address more than 8 MB (later versions could use up to 10 MB).
The 32-bit Mac OS
Apple introduced System 7 in 1991, the first version of the Mac OS with 32-bit support. Multitasking was a standard feature for the first time, 32-bit QuickDraw meant 24-bit color, and those Macs that supported 16 MB to 128 MB of RAM could finally use it.
Problem was those 68000-based Macs couldn't use 32-bit mode at all, as they were designed to function as 24-bit CPUs, and some early Macs with 32-bit CPUs had ROMs designed for a 24-bit environment - ROMs that were not compatible with 32-bit operation. These were called "32-bit dirty" Macs, and Connectix released a software patch (Mode32) to give them full 32-bit support.
From System 7 in 1991 through Mac OS X 10.5 today, through architectural changes from Motorola 680x0 CPUs to PowerPC CPUs to Intel CPUs, the Mac OS has been 32-bit.
The 64-bit Future
IBM designed the PowerPC 970 to handle both 32-bit and 64-bit instructions natively. The chip became known as the G5 when Apple introduced the Power Mac G5 in June 2003 as the first 64-bit personal computer. Just as Apple had sold Macs with 32-bit CPUs in the era of the 24-bit Mac OS, the G5 and most Intel-based Macs were 64-bit CPUs coupled with a 32-bit operating system.
Apple has slowly added a bit of 64-bit support - first with OS X 10.4.7 "Tiger" to allow more than 4 GB of RAM (although individual apps were still limited to using the old maximum), and adding additional 64-bit support in OS X 10.5 "Leopard". With OS X 10.6 "Snow Leopard", the entire operating system will have 64-bit capabilities - although it appears that most Macs will default to 32-bit mode, at least initially.
Benefits of a 64-bit Operating System
One of the primary arguments for 64-bit computing is breaking the 4 GB memory barrier. A 64-bit OS can theoretically support 16 exabytes (16 million gigabytes) of RAM, although none of today's personal computers can come anywhere near that. A few support 128 GB or more - which is horribly expensive - and most of today's Macs top out a "just" 8 GB.
As a low-end user, I've never had a Mac with more than 2 GB of RAM, and that has always seemed like plenty. Frankly, going beyond 4 GB isn't a real issue for most computer users.
However, there are places where you can benefit from 64-bit operation regardless of how much RAM your Mac has:
- Files over 4 GB in size are a reality - DVDs, disk images, video, etc. 32-bit operating systems struggle with them; 64-bit operating systems take them in stride.
- Data encryption/decryption can run 3-5 times faster in a 64-bit environment. This may apply to stuffing and unstuffing files as well. Think email attachments.
Complex numerical analysis is another place where 64-bit operating systems doing 128-bit math will be more accurate, but that's probably not significant to most computer users.
Drawbacks of a 64-bit Operating System
The biggest drawback of a 64-bit OS is that data occupies more space in memory - which can be offset by installing more RAM. One way of addressing this is to allow 32-bit operating within the 64-bit operating system. Snow Leopard fully supports 32-bit software when running in 64-bit mode.
The Road Ahead
The 8-bit era was relatively short, from the mid 1970s to the mid 1980s. The 16-bit era took off with the introduction of the IBM PC in August 1981 and started fading out with the introduction of Windows 95. The Mac's 24-bit era ran from 1984 through 1996, when Mac OS 7.6 was introduced with no 32-bit support. The 32-bit era began in 1995 on PCs and 1991 on Macs, and it remains dominant to this day.
The first 64-bit version of Windows for PCs was introduced in April 2005 (previous 64-bit versions of Windows supported PowerPC, Alpha, MIPS, and Itanium), and Apple began adding 64-bit support the Mac OS X in 2006. To this day, 32-bit Windows dominates. Microsoft estimated that over 25% of Vista users were 64-bit at the end of 2008, and some dealers are now seeing upwards of 50% 64-bit sales. Unfortunately for Microsoft, about 20% of Windows users are running Vista, so perhaps 6-7% of Windows users have gone 64-bit at this point.
Windows 7 is expected to be the last version of Windows available with 32-bit mode, and already projections are that over half of all users will choose the 64-bit version. Windows 7 could be attractive to Windows XP users (75% of all Widows users!) with relatively up-to-date hardware.
Mac users are blessed - we don't have to choose whether to buy a 32-bit or 64-bit OS - Snow Leopard installs both. At this point, about 75% of Mac users are using Intel-based Macs, 25% PowerPC hardware. The adoption rate for Mac OS X 10.5 has been very high, outnumbering 10.4 users about 3.5:1 - and the ratio is probably higher on Intel Macs than PowerPC ones.
Looking at a $29 upgrade fee for Snow Leopard and assuming Apple is going to actively market it to the installed base, I'm guessing that 2/3 of current Intel Mac users will make the upgrade and over half of all Mac users will be on Snow Leopard by the end of the year.
The road ahead is 64-bit, and it appears to be a long road. There are no 128-bit CPUs available for personal computers, and there doesn't appear to be any reason for them in the foreseeable future.
The road ahead is multicore computing with 64-bit CPUs and 64-bit operating systems. While many of us may continue to work and play productively with 32-bit operating systems for years, 64-bit computing will be the norm by the end of 2010.
We're fortunate that Apple is making the migration easy.
Dan Knight has been using Macs since 1986, sold Macs for several years, supported them for many more years, and has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.
Recent articles by Dan Knight
- The Late 2012 iMac Value Equation, 2012.10.31. Thinner, lighter, faster, USB 3, improved graphics, Fusion Drive option, and no SuperDrive sum up the new iMacs.
- The 13" Retina MacBook Pro Value Equation, 2012.10.30. Take the 13" MacBook Pro, add a Retina Display, remove the SuperDrive, and drop almost a pound from its weight.
- The Late 2012 Mac mini Value Equation, 2012.10.29. The entry-level Mac mini is a nice step up, but the top-end quad-core model is a powerhouse.
- More in the Mac Musings index.
Links for the Day
- Mac of the Day: Centris 610, introduced 1993.02.10. This was the Mac we used when we started Low End Mac in 1997.
- May 24 in LEM history: 99: Mac sales up, iMac sales down? - 01: Speeding up digital photography - 02: The Internet, research, and plagiarism - 04: NewerTech TiBook battery - Optical mice from Contour - 06: Power Mac today or Intel tomorrow? - 07: G5: Apple's last fling with PowerPC - G3: From 233 MHz to 1.1 GHz
- Support Low End Mac
Recent Content on Low End Mac
- World Book Encyclopedia 2012 DVD, Tommy Thomas, Reviews, 2013.03.05. "You may be asking yourself, in an age of Wikipedia and instant information, is World Book still relevant?"
- Vintage Computer Festival SouthEast, April 20-21, 2013, Simon Royal, Mac Spectrum, 2013.02.25. Old Apple gear and old PCs.
- iMessage: The Ultimate Messaging Service?, Simon Royal, Mac Spectrum, 2013.02.21. In most ways, Apple's iMessage is far superior to BlackBerry Messenger.
- More links in our archive.
- Best Mac mini Deals
- Best 13" MacBook Pro Deals
- Best Intel iMac Deals
- Best iPod touch Deals
- Best iPhone Deals
- Best iPod nano Deals
- Best iPod classic Deals
- Best Apple TV Prices
- More deals in our archive.
Low End Mac Reader Specials
Cult of Mac
Shrine of Apple
The Mac Observer
Accelerate Your Mac
The Vintage Mac Museum
Mac Driver Museum
System 6 Heaven
System 7 Today
the pickle's Low-End Mac FAQ