Hardware Reference
In-Depth Information
The desktop system was from about 48% to 55% faster than the laptop on USB transfers,
yetonly1%to3%fasteronFireWiretransfers.Inotherwords,theFireWiretransfertimes
were virtually
identical
on both the desktop and laptop systems, even though the systems
varied greatly in speed. This is understandable because FireWire uses a peer-to-peer con-
nection design, which does not use the PC to manage the interface. On the other hand,
USB is a PC-centric design using the PC as the host controller. In other words, because
of the internal design differences in USB and FireWire, the PC processor and overall PC
system performance have a much greater effect on USB than on FireWire.
Another interesting point: The method used to copy the file (
COPY
versus
XCOPY
in this
case) actually made
more
of a difference than the interface or the system speed. This
brings up many more questions: Would there have been other differences had the drive
been formatted with NTFS instead of FAT32? What if I had copied many small files in-
stead of one large file? What if I had used a different operating system (OS)? As you can
see,inanybenchmarkorcomparison,youmustconsiderahugenumberofvariables—and
there are no simple answers to ambiguous questions!
Hot-Plugging (and Unplugging)
BecauseexternalUSBand1394(FireWire)devicescanbehot-plugged,youmustbecare-
fulinsomecaseswhenunpluggingthings,especiallystoragedevices.Tohelppreventdata
loss with external drives and storage devices, when disconnecting them you should click
the Safely Remove Hardware icon in the Windows taskbar notification area (often called
the
system tray
). Then select the device to be removed and wait for the system to indicate
that the device can be safely removed before you unplug it.
But consider this: I've unplugged devices without “safely removing” them many times
without problems, so is it really necessary to go to the trouble? To answer that question
properly, I'll have to explain more about how caching works, both in Windows and in the
hardware.
Windows includes a write cache in the OS (using system RAM) Microsoft likes to call
lazy write
.TheOS-basedlazywritefunctionhasbeenaroundforalongtime.Infact,ithas
been enabled by default for nonremovable drives (internal ATA hard drives, for example)
in all versions of Windows since version 3.1 (as smartdrv.exe), which dates from 1992.
What Microsoft calls lazy write is also called
write-back caching
,
write-behind caching
,
and
deferred
or
delayed writes
.
In modern versions of Windows, this is controlled by the Windows cache manager. The
cache manager controls Windows-based write caching and flushes the cache quite of-
ten to minimize loss. In addition, any application that uses write operations can request
that those operations be done as
write-through
, which bypasses the lazy writer and goes
