[xplorer˛] — Copy throttle control
home » blog » 17 February 2008

"Good things come to those who wait" — Guiness

Transferring big files in windows is a trying experience based on totally rubbish hardware and software architecture. The copy progress seem to suck up all the machine resources, both CPU and hard disk go ballistic, and the GUI responsiveness is on par with the manoeuvrability of a small oil tanker. This problem has been going on for ages and it is unlikely that it will ever be corrected. Whoever in microsoft is responsible for this disgrace should be hit with shoes and/or have mosquitos installed in their house.

Whereas most windows users can only submit to this fate, cursing redmond — to ease the pain, xplorer˛ users can do something about it. A feature of robust transfers is the copy task priority. When you start a large operation using Edit > Copy to or <F5> command, you can select the task priority from copy options dialog. Setting this to background you force the thread in a state that will consume less resources if you are busy doing other things on your computer. The transfer rate is reduced somewhat, meaning that the copy will take longer, but this is a small price to pay for the freedom to continue your work!

The latest xplorer˛ version 1.71 introduced a new measure to make the transfer even slower. The optional registry setting nCopyThrottleMS forces a millisecond delay after each 64KB file portion is copied. The transfer speed is dramatically reduced, but so is the slowdown of your system. The table below lists average transfer speeds for a 18MB file using different settings for the copy delay through the registry settings editor. These speeds will differ on your system but their relative magnitude will be similar.

Transfer speed
0 (default)2730.0

Based on these experimental measurements, a 100ms delay is an acceptable trade-off. You may want to set it larger or smaller to taste, e.g. if you need to save bandwidth for network file transfers, increase the delay. If you are in a hurry just use drag-drop which isn't throttled in any way.

Another problem with windows file copy is parallel operations. If you have two or more transfers going on simultaneously, especially if they share the same hard disk as source or target, things will go slower all over! Instead of copying full speed, windows will waste time moving around the hard disk read head between the parallel tasks. Overall the transfer rate will be less than halved and the GUI unresponsive. xplorer˛ solves this problem using queues.

Instead of running two copies in parallel, you tell xplorer˛ to queue transfers. Only one operation will be active at a time, and when this finishes, the next one will commence. At any time you can examine what's scheduled for copying using Edit > Queue status menu command. The latest version 1.71 has improved the information available, so you can see names of files that are queued.

Like my granma would say, "I go slowly because I'm in a hurry!". File copying is a proof for this apparent oxymoron.

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