General :: Why Is Reading A FILE Faster Than Reading A VARIABLE?

I don't understand the results of a simple performance test I ran using two basic scripts (running on a high end server):

perfVar.zsh :

#!/bin/zsh -f
MYVAR=`cat $1`
for i in {1..10}

[code]...

Performance test result:

> time ./perfVar.zsh BigTextFile > /dev/null
./perfVar.zsh FE > /dev/null 6.86s user 0.32s system 100% cpu 7.177 total
> time ./perfCat.zsh BigTextFile > /dev/null
./perfCat.zsh FE > /dev/null 0.01s user 0.10s system 91% cpu 0.118 total

I would have thought that accessing a VARIABLE was way faster than reading a FILE on the file system... Why this result ?Is there a way to optimize the perfCat.zsh script by reducing the number of accesses to the file system ?