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 Post subject: What's the deal with Hybrid drives, Turbo memory, and Vista?
 Post Posted: Sun Jun 17, 2007 1:51 am 
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Vista's enhanced SuperFetch cache can use flash memory to store additional
cache data. The flash memory can be attached or accessed 3 different ways:

Code:
 PCIe - Intel Turbo memory (Vista ReadyBoost)
 SATA - Hybrid drives (Vista ReadyDrive)
 USB  - USB key/thumb flash memory drives (Vista ReadyBoost)


Microsoft refers to the basic improved caching technology in Vista as
SuperFetch. Microsoft uses the term ReadyDrive to refer to SuperFetch using
Hybrid drives, while ReadyBoost refers to SuperFetch using either PCIe flash
(Intel Turbo memory) or USB flash memory.

Of these connections, PCIe offers the highest bandwidth, however in general it is
the flash memory that limits bandwidth more than the bus. Flash is *much* slower
than RAM, and even slower than hard drives for larger sequential
reads/writes.

Since interfacing to the flash via a dedicated PCIe slot offers the highest
bandwidth, it is no wonder that Lenovo thinks that Turbo memory is the better
of these flash technologies:

Hybrid Hard Disk Drives - Performance Not There Yet
http://www.lenovoblogs.com/insidethebox/?p=46

Intel Turbo Memory
http://www.intel.com/design/flash/nand/ ... /index.htm

Intel Turbo memory was codenamed Robson Technology prior to release:

Overcoming Disk Drive Access Bottlenecks with Intel Robson Technology
http://www.intel.com/technology/magazin ... n-1206.htm

The Lenovoblog entry indicates that Turbo memory is "purported to work with
Windows XP", however currently only Vista is supported:
http://downloadmirror.intel.com/13232/E ... eNotes.htm

Theoretically, if a SuperFetch add-on process or cache driver was written for
XP, it should be able to use the same flash memory devices in the same manner
as Vista.

Most current Hybrid drives have only 256MB of flash, and most current Turbo
memory cards hold 1GB. I would expect to see 2GB and 4GB Turbo memory cards
long before that much flash appears in a Hybrid drive. While you can get USB
key/thumb drives with 4GB or more, Vista currently limits ReadyBoost to 4GB.
SuperFetch compresses and encrypts the data stored in flash, usually
resulting in a 2:1 ratio, meaning 4GB of flash can store about 8GB of data.

SuperFetch can improve performance by decreasing program load/save and system
hibernate/resume time. However since RAM is much faster than flash, if you
have more RAM, SuperFetch will use that for caching instead of flash memory
anyway. This explains why test reports indicate that once you have 1GB of RAM
(or more), there are little if any benefits from SuperFetch using flash
(ReadyBoost or ReadyBoot).

Is Intel's `Turbo Memory' really turbo?
http://www.tgdaily.com/content/view/31976/135

ReadyBoost Performance
http://www.anandtech.com/systems/showdo ... i=2917&p=6

Also consider that flash memory wears out (a given cell can only be written a
limited number of times). Statements by Intel have indicated that its Turbo
memory devices should last around 5 years, but this should vary depending on
the size of the cache. The higher the capacity, the more writes can be spread
out to avoid re-using cells. Sort of like rotating tires this helps keep wear
on all cells even as opposed to wearing out certain cells sooner than others.

In the end, the only useful benefit from this technology might be slightly
longer battery life for laptops. Unfortunately since this technology is
currently available only for Vista, any increases in battery life due to
ReadyBoost/ReadyDrive probably won't offset the overall battery life
reductions in using Vista as compared to XP:
http://news.zdnet.com/2100-1040_22-6181366.html

Bottom line: I'm not too excited about this technology, as you would be
*much* better off spending the money on 1GB of RAM (or more) and/or a faster
*non-hybrid* drive instead. Scott.

EDIT: Note that the (now obsolete) "hybrid" drives described here are nothing like the *new* hybrid drives such as the Seagate Momentus XT, which work under any OS (no special drivers or software required) and offer near SSD performance for 1/5 (or less) the price. Scott.


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