Tuesday, December 16, 2008

Intel vs. PowerPC Macs

I recently purchased a new Intel Macbook to replace my trusty iBook G4. Much has been written about the Apple's switch from PowerPC to Intel processors and there is no denying the market power of Intel, but I have some comments now that I have spent a little time with both kinds of Mac.


When comparing Intel and PowerPC micro processors, a common theme used to be the Intel complex instruction set (CISC) vs. the IBM reduced instruction set (RISC). This line of reasoning may have had some merit in the 1980s or early 1990s, but processor architecture has blurred, with each family incorporating the best designs of the other. I don't read much about this any more because it mostly doesn't apply.

Big endian vs. little endian

The endianness of a processor refers to the byte order of data in memory. Specifically, big endian processors, (traditionally the PowerPC line), stored the most significant bytes first, while little endian, (the Intel line), stored the significant bytes last. If you have ever debugged data or instructions in memory, big endian is the logical way you would expect to see things, a more natural or human way to read memory. Little endian data looks garbled to me.

I started my programming life long ago on an IBM mainframe (big endian) and wrote quite a few lines of assembly language. I actually enjoyed working with the mainframe register architecture and assembly was a joy. When I started working with Intel PCs, assembly language became a nightmare. The registers could be addressed partially using one mneumonic, fully with another, and the debugger showed bytes in the strange little endian order. It was a real buzz kill.

Today, with optimizing compilers and high level languages, it doesn't make much difference any more. Most modern languages are so high level (my current favorite is Ruby), that endianess is transparent. Some processors can even be programmed to change their endianess. So, other than personal preference, and a slight distrust of engineers that prefer little endian, this is a difference that doesn't carry much weight.

Power, heat, and batteries

PowerPC processors have nearly always been more power efficient than Intel. This translates into less heat (less time running a cooling fan), and longer battery life. The battery life between my new Intel Core 2 Duo Macbook and my G4 iBook is dramatic. Even though the G4 is over 2 years old, it still gets about an hour and half of extra battery life. Certainly, part of that is because it also has a smaller and dimmer screen, but the processor architecture is also a factor. I was shocked at how fast the Macbook battery ran out the first week I had it. It is still better than a Windows laptop, but a step backward compared to the G4.


The operating system was not the only thing that had to be compiled to run on Intel processors. To take advantage of native speed, every application had to be recompiled. Some software vendors took their time building Intel binaries. Apple provided the "Universal binary" solution ahead of the switch so the application hit wasn't too harsh.

The virtual plus

Apart from the ability of Intel to supply Apple with enough processors, the switch enabled fast virtual machine technology that doesn't rely on software emulation to work. Applications like Parallels and Vmware Fusion give the Intel based Macs a vastly improved capability to run Windows, Linux, and other operating systems with OS X as the host. I tried running Linux on the free Q virtual machine on the G4 and it was almost too slow to use. Running VMware Fusion, I have a couple of Linux distributions running graphical X desktops at near native speed. In this sense, the switch to Intel was a virtual plus.

Does it matter?

How you weigh the positives and negatives above determines how you view the switch. In the end, the best things about a Mac still exist in the Intel world, and apart from the good folks at IBM, Motorola, and Intel, most people won't notice.