[thelist] Really dumb question...

[Judah McAuley]

Ken Kogler wrote:
> AFAIK, IE (and I would assume other browsers) can download multiple items
> (parts of a page) at once. If IE is downloading at 5Kb/sec, then the two
> sliced up 10Kb graphics will appear on my screen fully rendered as one
> graphics in 2 seconds. However, at 5Kb/sec, one 20Kb graphic (the same
> thing, just not sliced) will take 4 seconds to show up... twice as long.
>
> Of course, this whole thing depends on the observed behavior of multiple
> graphics on a page downloading at once... have I been hallucinating? Is this
> just IE-specific?

Downloading multiple things at once is known as HTTP pipelining and is a
feature of all http 1.1 compliant servers.  As far as browser support
goes, it depends.  Mozilla 1.0, for example, does not have pipelining on
by default.  I'm unsure about various versions of IE.

That being said, it also depends on bandwidth.  If I've got a modem that
is maxing out at a generaous 5KBps your 20 KB graphic will download
faster than your two 10 KB graphics.  Why?  In the best case scenario,
the two 10 KB images would each be downloading at 2.5 KBps.  Therefore
each image would take 4 seconds to download.  But since there is
pipelining, they both download simultaneously in 4 seconds.  The 20 KB
image would get downloaded at 5 KBps also requiring 4 seconds of
transfer.  So why is the 20 KB image going to download faster?  Because
of the overhead involved in TCP connections.  Two 10 KB images requires
two TCP negotiations.  One 20 KB image only requires one negotiation.
Transfers are typically slow at the beginning while the connections are
set up and settled down and then transfer speed picks up.  For long
connections the initial setup is negligable.  For many short
connections, the overhead becomes appreciable.

Hope this helps,
Judah