Introduction

The next Centrino platform to be released next year – codenamed Santa Rosa – will feature an integrated disk cache using flash memory in order to speed up disk access and also save energy – which is a must in extending battery life. In this IDF Fall 2006 we had a more detailed explanation on how this technology, codenamed Robson, will work. Let’s take a look.

First, why Intel is creating this technology? If you take a look on a typical disk access, the majority of the time is spent moving the mechanical parts of the disk rather than transferring data, as you can see on the example given on Figure 1.

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Figure 1: The majority of the time is spent on mechanical latency rather than actually transferring data.

The second problem is that the CPU is way faster than the hard disk drive, causing a performance bottleneck on the system: when the CPU needs to read something from the hard disk drive, it has to wait until the data is delivered in order to manipulate it.

In the last 10 years the problem only got worse: while CPU performance increased 30x, hard disk drive performance increase only 1.3x.

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Figure 2: Hard disk drive performance didn’t follow CPU performance increase in the past 10 years.

So what Intel is proposing with Robson technology is a cache solution using flash memory between the CPU and the hard disk drive. The idea is to make the CPU to access this flash memory as much as it can instead of going all the way to the hard disk drive, which, as we explained, slows down the CPU. So this flash memory will basically hold the most frequently accessed data in order to speed up disk access.

Intel showed us some preliminary performance data (see Figure 3), using a Photoshop workload. In their test using an 1 GB flash disk cache improved the hard disk drive transfer rate by 463%, making the time spent to run the workload to drop from 24.5 seconds to 12.4 seconds.

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Figure 3: Performance impact of Robson technology.

It is not only that. As the hard disk drive will be less accessed, it will consume less power and thus produce less heat. Of course the more cache hits – i.e. the more the CPU accessed the cache instead of accessing the hard disk drive directly – the more power savings, as you can see on Figure 4.

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Figure 4: Hard disk drive power savings with the use of Robson technology.

Robson technology also speeds up the notebook coming back from hibernating state. When you put your notebook to hibernate, what the system does is to save on hard disk drive the contents of the RAM memory. When you wake it up, the system transfers the contents of that file back to RAM, restoring all programs and data that your were working when you put your portable computer to sleep.

With Robson, this file is stored on flash memory rather than on the hard disk drive. So when you wake up your PC, it will come back faster as the transfer rate of the flash memory is far higher than the one provided by the hard disk drive.

Of course if you have more RAM memory than Robson memory your notebook will still need to the hard disk drive to store the remaining contents that didn’t fit the flash memory. Even when this occurs the difference in time will be quite visible.

Let’s now take a more in-depth look on how Robson technology will be implemented.

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