External Hard Drive shrinks after partitioning several times

first off, congratulations having great , helpful forum, have been reading long time , found many times useful , full of resources.
since first post here, hope right thread topic.
using external hard drive 2 partitions: 1 time machine , second storing files on windows , mac.
after resizing partitions several times trying figure out right size each, reformatting , re-partitioning lion's native disk utility, have noticed each time space less , less without files on it, point total available capacity of external disk (and partitions accordingly) has been reduced in 300 mb compared first partition did on it.
have been reading , looking explanation can't seem find neither reason nor solution problem.
know reason , whether , how can restored original size of 1tb?
input appreciated, thank you.

 

depending on comfort level terminal, can use diskutil list give more information disk utility partitions. example, here info mine:

code:

 username$ diskutil list /dev/disk0    #:                       type name                    size       identifier    0:      guid_partition_scheme                        *160.0 gb   disk0    1:                        efi                         209.7 mb   disk0s1    2:                  apple_hfs mbp_lion                159.2 gb   disk0s2    3:                 apple_boot recovery hd             650.0 mb   disk0s3 /dev/disk1    #:                       type name                    size       identifier    0:      guid_partition_scheme                        *500.1 gb   disk1    1:                        efi                         209.7 mb   disk1s1    2:                  apple_hfs media                   499.8 gb   disk1s2  

 

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