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USB Flash drives are useful for many things, but not for running your system from them long term. We'll look at why, and a Windows Vista alternative.

I see large USB flash drives are very cheap. My 'C' drive is partitioned to be 8GB, on which I have my Windows OS (Win 2K, in my case), and all my program installations. All my data files go on other partitions/drives.

So I'm thinking that for a little extra money, I could have my C: drive run off of flash Memory, instead of a hard drive (if the PC maker makes it possible). How much faster would Windows and all my boot-up programs load if this were the case (My current configuration take about 2-3 minutes for full reboot)? How much faster would Word, or Excel start up (not counting the file that it would be loading off of the accompanying HD, which would only be used to store data/document files)?

I often get questions where people want to use flash memory in various forms to speed up the normal operation of their computer. There's a lot of misunderstanding of flash memory and what it's capable of.

The good news is that while you still can't use USB flash drives for RAM, and you still shouldn't use them for your "C:" drive, Windows Vista has a new feature that will let you use them for something sort of in-between.

Why USB flash drives don't work as system RAM.

I've covered this before in an article Can I use a USB RAM stick to increase system memory?.

To summarize: system RAM is connected directly to your CPU on the motherboard via an extremely high-speed interface.

When the system accesses a USB flash drive it has to actually go through the USB device drivers and the comparatively much slower USB interface. Even USB 2.0 speed pales in comparison to the speed of on-board RAM.

In short, PC hardware simply isn't set up to treat an external device as true system RAM. And as we'll see in a moment, you don't really want it to anyway.

Why USB Flash Drives make bad system drives.

Flash memory wears out. The more frequently you write to a flash drive, the sooner it will fail. Eventually it won't be able to "hold" the data written to it.

You don't hear about it much, because the numbers of writes we're talking about are in the 10,000 to 100,000 range or higher. If all you're doing is periodically copying files to and from your USB flash drive, you can probably do that for years before you have a problem.

The problem becomes more apparent when you run applications that write to the drive a lot.

Windows definitely writes to the drive a lot. Windows is constantly updating the registry, swap files, and depending on how you use your machine, many, many other things.

If you were to use a USB flash drive as your system drive it might work for some time depending on how you use it. Booting from a flash drive often results in exactly this scenario. But using it constantly or planning to use it long-term is a trip down a one-way path: eventually the flash memory will fail.

This is another reason why you don't want flash memory as RAM: the system writes to RAM at a much more rapid pace than even the hard drive. Flash memory just won't last.

My earlier article, Can a USB thumbdrive "wear out"?, has more discussion of this situation as well.

Enter Windows Vista and "ReadyBoost"

"ReadyBoost is not RAM, and it's not really your system drive. It's something in-between."

So after publishing that USB RAM stick article last year, I started to get push-back. The common refrain was "You're Wrong! Windows Vista lets you use USB memory as RAM!".

No. Not quite.

There's nothing about Windows Vista that made the issues above go away.

Windows Vista does, however, include a nifty new feature that allows you to use USB Flash Drives to enhance performance in the form of something they call "ReadyBoost".

ReadyBoost is not RAM, and it's not really your system drive. It's something in-between.

What Windows does with ReadyBoost (and the feature it relies on, "SuperFetch") is in a sense, notice which programs you run a lot and pre-load them. To quote the Microsoft web site:

SuperFetch monitors which applications you use the most and preloads these into your system memory so they'll be ready when you need them.

ReadyBoost is nothing more than allowing SuperFetch to preload those applications into your USB Flash Drive.

The pre-load happens relatively infrequently; preserving the life-cycle of the flash memory. But reading the preloaded applications from the flash memory is typically faster than reading from your hard drive. Depending on how you use your computer it may improve performance.

But it's not RAM. And it's not Windows "running on" the USB Flash Drive.

Back to your question.

To actually answer your question: it's hard to say how much faster your system would be, that depends on too many things we don't know. However it's safe to say that it would be faster - until it crashed and died. Depending on the specific hardware involved and how you use your system that could be a day, a month, or if you're lucky, maybe a year.

But ultimately it's a game of Russian Roulette.

You'd be better served, in my opinion, by adding actual RAM to your system. It's possible that adding a second hard drive to your system and moving the system swap file to that drive, moving installed programs to that drive, or moving your data to that new drive might also speed things up for you.

Article C3051 - June 10, 2007 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

Dave B
June 11, 2007 2:46 PM

Everything I've found has shown that Readyboost has limited influence on the system's performance. If the computer has less than 1 gigabyte of RAM (perhaps 512M), Readyboost can enhance the system performance. However, the same machine will see dramatically faster performance by increasing the system memory (RAM) to at least 1G and even more at 2G. One of our family's machines only has 1G of RAM, some of which is allocated to use by video, so the available RAM is less than 1G. I jammed a USB thumbdrive into the back of the machine - but I don't have any measurable results to show it is any faster.

Folks interested in reading more, can find an interesting article over on AnandTech:

Eli Coten
June 16, 2007 3:25 PM

I have experience of running software programmes from a USB flash-drive and have always found them to be slower in comparison to running them off a hard drive.

I have tried both Firefox & Thunderbird portable, as well as storing & using Outlook.pst files on a flash drive and whilst Outlook was unbearably slow, Firefox & Thunderbird run much slower from a thumb-drive than they do from a magnetic-hard drive profile.

Therefore I would extend that to say that booting off a flash drive would not only wear out the flash-drive incredibly rapidly, but in addition would likely slow everything down as well.

I believe flash drives are good for long continuous writes but if you are reading and writing lots of tiny bits of data all over the place the access time or delay between each individual read and write operation becomes noticeable.

This is only my theory based on what I've seen in practice, so it may be wrong but certainly my experience shows that flash drives are no good for running software of any kind from.

December 23, 2008 7:04 AM

I've seen some improvement with one flash drive, and degradation with another. Not all flash drives are fast enough. If you do this sort of thing, make sure to get a fast flash drive and benchmark it. I have one drive that's great for sequential read, but terrible for random reads and it was very slow for readyboost.

March 9, 2009 1:01 PM

If you get a very fast SLC drive to use as C, you will get a faster system. But a fast 8GB CompactFlash disk($100-200) is at a cost of well more than the $50 of a small(80GB) fast hard drive. The power difference is negligible, the noise difference is small(I actually had a CF disk make more electrical noise than my HD did mechanical noise,) and the only big advantage is if you drop it while it's running.
I would rather have more space.

Count Turdular
November 30, 2010 8:17 AM

I use a USB Flash drive as my Notebook PC's main boot drive, running Ubuntu 10. It works fine, although fairly slowly (because I am using a slow Kingston Datatraveller, a Sandisk would be faster) and space is restricted to the 4GB of the flash chip. I have used it for around 4 months without any dieing memory problems, although i often have to create space for virtual memory by deleting files. Even some Windows games work in Wine (I have Max Payne installed on a separate 1GB flash drive), so I am quite impressed with it really.

Really, this is only a stop-gap until I buy a new HDD for the laptop, it is too slow to be a permanent solution - but it was a good experiment to show how well a USB flash drive can cope with the many read/writes made by an OS. Not a viable option for permanence though, but useful as a temporary solution.

April 29, 2012 12:42 PM

I had a discussion with a friend who is into video games; he bought a flash drive specifically to get the speed advantage, and better "gaming".

The friend procure a highly rated flash drive, in 2011. I ask him to send me a snapshot of the performance indicator using (under Windows 7, 64 bit OS) perfmon (type perfmon the blank "search programs and files") - " this "box" is in the index when you want a listing of all the other programs available), This opens the resource monitor ( will attempt a snapshot below), after a few simple steps, one can get the bytes per second transfer rate from the hard/flash drive. Basically - one of the most intensive video games did NOT come close to using 50% or so of the maximum speed/performance of a Flash Drive, a hard drive would of given the same performance or similar performance.

I would assume, if a video game does not use the maximum performance of a flash drive, few other "main stream" programs would either.

Sorry can't post a snapshot of the data rate for the disk drive here.

April 29, 2012 12:50 PM

I had similar thoughts about why the boot time has not as improved as dramatically as other area's in computers ( PC ).

A partial answer is I have a relatively high end motherboard. Supermicro C2SBX, which uses 250 Watts when running. The boot BIOS is a one ( 1 ) bit serial chip. That explained one main reason my MB takes awhile to boot.

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