Not enough RAM and a conventional hard drive will cause
performance to slow down just a tad.
Written by Ctein
[Author's note: I'm hard at work on the third edition of my book Digital Restoration from Start to Finish. Here's an excerpt for your enjoyment and edification.]
Whether you're using Photoshop or some other image processing program, maximizing its performance is especially important when doing photographic restoration. It's easy to generate huge files, bigger than what you're likely to be working with from a digital camera. For example, an 8x10 photograph scanned at 600 PPI in 16-bit color yields a 30 megapixel, 180 MB file. I'll be talking about Photoshop, specifically, but if the image processing program you're running can make use of a scratch disk when it runs out of RAM, the same general advice will apply.
Here's the non-technical version: Stuff your computer with as much RAM as it will support. RAM is cheap. Less than 8 GB will badly cramp your style. Working on a large and complex restoration, double that is barely adequate. My 27" i7 Retina iMac has 32 GB of RAM, 24 GB of which are allocated to Photoshop. You want to leave enough RAM free for other machine functions so that they don't choke—75% is a safe amount to give Photoshop. I can still run out of RAM in Photoshop on occasion…but it's a lot less common now than it was on my old system, which only had half as much memory.
Next, after maximizing your RAM, get an internal SSD (solid state drive) and use it for your operating system, applications including Photoshop, and the scratch disk. You should also put the photograph you're working on there. That doesn't require a very large SSD. A 256 GB SSD will handle this with plenty of room to spare. You can put all your data files and photographs that you're not working on on a different drive. Of course, there's nothing wrong with getting a big one and putting everything on it, including all your data files, but they're a lot more pricey.
A hybrid or “Fusion” drive doesn't really cut it for photo restoration. They marry a small solid-state drive to a conventional hard drive. That speeds up activities that demand accessing only a few gigabytes of data, like launching and relaunching applications, working with text and spreadsheets, and so on. The thing is, the scratch files that your image processing program will generate when it runs out of RAM are huge. They'll swamp the solid-state part of the hybrid drive, and then it performs no better than a conventional drive. Don't get me wrong; they're a distinct performance improvement over a traditional hard drive—but nowhere what you'll see with a pure SSD.
Now I shall get geekily specific. Those of you who don't care, you can skip to the end. You won't miss much.
To convey to you a sense of just how much difference sufficient RAM and an SSD can make, I ran a set of benchmark tests using Lloyd Chambers Photoshop benchmarking actions. They're designed to stress the heck out of Photoshop. For these tests, I used the medium scale benchmark, diglloydMedium, because the small one simply ran too fast on my new machine to do accurate timing, and it didn't push huge amounts of data to the scratch disk.
I first ran the benchmark with Photoshop allocated its full 24 GB of RAM. That's enough RAM that Photoshop didn't have to use the scratch drive. It ran diglloydMedium in a little over 11 seconds with a maximum CPU usage of over three cores (300+%), and it ate up about 15 GB of RAM.
Good enough. Then, what happens when Photoshop runs out of RAM, as it will on an under-equipped computer? I cut the Photoshop allocation back to 4 GB of RAM and ran the same benchmark with the iMac's internal SSD as the scratch drive. Even though data transfer to the scratch disk peaked out at over 900 MB/sec, the time to execute the benchmark almost tripled, to 30 seconds, and CPU usage barely exceeded 100%.
Next I took the SSD out of the picture. I changed the Photoshop scratch disk to a fast external conventional hard drive. This, by the way, is the way you should be running if you don't have an internal SSD as your system drive. If your system drive is a regular hard drive, putting the scratch files there only sets you up for what's known as “drive thrashing.” The disk head has to bounce all over the place to keep up with the competing demands from the OS, the running programs, and the scratch space, and that slows things down horribly. Not a problem with an SSD.
With 4 GB of RAM and a conventional hard drive disk, performance just cratered. The runtime was two minutes with a peak data rate of 150 MB/sec to the drive. CPU usage barely got to 30%.
In summary, running with insufficient RAM and a conventional hard drive slowed the benchmark by a factor of ten!
Photo-writer, sci-fi novelist, and physicist Ctein is TOP's Technical Editor.
©2015 by Ctein, all rights reserved
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