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Processors and Cores

Photoshop loves a speedy central processing unit (CPU), particularly as you pile on the megapixels, layers, and Smart Objects. CPU makers used to boost performance by increasing the CPU speed in gigahertz (GHz), but started hitting a wall in terms of heat and power consumption. In recent years, CPU design has shifted from speeding up one processor core to including multiple processor cores in a single CPU. Now it's easier to find a computer with two 2 GHz cores than with one 4 GHz core.

Photoshop has recognized multiple processors for several versions now. However, it's important to understand that two 2 GHz cores are not exactly as fast as one 4 GHz core. Overhead is involved in splitting the workload across the cores, and moving data between the cores takes time. Some operations aren't even practical to split across cores. In some cases, today's four-core and eight-core computers can process data faster than the memory bus can deliver more pixels to be processed, resulting in cores that wait for things to do. Multiple cores are beneficial when you have multiple applications that each require high CPU usage, or multiple processes that don't depend on each other, such as rendering video frames.

Multiple cores are most effective when doing a lot of processing on a relatively small data set. However, editing a Photoshop document usually involves moving high volumes of image data between the CPU, RAM, and disks, so the transfer speed between those components is a common bottleneck. To make the most of a multiple-core computer with Photoshop, you need enough RAM to minimize disk access. When disk access is inevitably required, you want disks that are fast enough to minimize delays in getting data to the RAM and CPU. If you're talking only about Photoshop, the speed gain of an eight-core computer versus a four-core computer isn't necessarily proportional to the price difference between them. This situation could change quickly as motherboard designs and operating systems are updated, though. If you're trying to make a purchase decision, be suspicious of specs that quote CPU speed improvements alone, without accounting for the other components. We advise you to research Photoshop-specific performance benchmarks for any computer you're thinking about buying.

64-Bit Processing

Many people anticipate huge performance gains from the newer CPUs that can process 64 bits of data at a time, compared to the 32-bit CPUs that have been in use for years. Sounds twice as fast, right? Well, not automatically. To get the most out of a 64-bit CPU, you also need the following:

  • A 64-bit operating system. For example, it isn't enough to have Windows Vista; you need the 64-bit version of Windows Vista. (Photoshop CS4 doesn't officially support 64-bit Windows XP.) On the Mac, it's a little more complicated. Mac OS X 10.5 is the first Mac operating system to have 64-bit support throughout the system, and Adobe had originally planned to make the Mac version of Photoshop CS4 support 64-bit operation. However, because Apple unexpectedly removed 64-bit support for legacy (Carbon) applications, Adobe won't be able to provide a 64-bit Mac version of Photoshop until after CS4.

    If you have a Mac with a 64-bit processor and have a legitimate need to run 64-bit Photoshop CS4 now, you could try running the Windows version of Photoshop CS4 in 64-bit Windows Vista under Boot Camp. Yes, we realize that this isn't an ideal 64-bit solution for Mac users (like us).

  • Well over 4GB of RAM. One of the biggest benefits of 64-bit computing is that Photoshop can directly use more than the roughly 3GB of RAM that it can use under 32-bit computing. If this improvement appeals to you, don't upgrade to just 4GB, or you won't see much difference. Aim for 8GB to start, and go higher if your files are big enough to need it.

    In 64-bit Windows Vista, the edition you use determines the maximum amount of RAM the system recognizes, ranging from the 8GB supported by the Home Basic edition to the 128GB limit of the Ultimate edition.

  • Really big files. The ability of a 64-bit processor to address much more RAM directly speeds up the processing of very large files. If you work with Photoshop files that are over 1GB in size, you should see major performance gains from 64-bit Photoshop. But if you mainly make simple edits to five-megapixel JPEG camera files without using many layers, masks, or Smart Objects, 64-bit Photoshop probably won't feel much faster.

Choosing 64-bit over 32-bit computing is like driving a 64-passenger bus instead of a 32-passenger bus. The 64-passenger bus can potentially move twice as many people in a single trip. But if you rarely carry that many people, the 64-passenger bus is no faster than the 32-passenger bus, and because it's bigger, it may actually cost you a bit more in overhead when it isn't being used to capacity. A 64-bit system can actually be slower than 32-bit when editing small files or when not much RAM is installed.

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