请大家帮看看这个，不明白

[root@pacific-lzh ~]# yum install kernel
Loading "fastestmirror" plugin
Loading mirror speeds from cached hostfile
* fedora: opensource.nchc.org.tw
* livna: ftp-stud.fht-esslingen.de
* updates: opensource.nchc.org.tw
fedora 100% |=========================| 2.1 kB 00:00
livna 100% |=========================| 2.1 kB 00:00
updates 100% |=========================| 2.3 kB 00:00
Setting up Install Process
Parsing package install arguments
Package kernel - 2.6.23.15-80.fc7.i686 is already installed.
Package kernel - 2.6.21-1.3194.fc7.i686 is already installed.
Resolving Dependencies
--> Running transaction check
---> Package kernel.i586 0:2.6.21-1.3194.fc7 set to be installed
--> Finished Dependency Resolution
--> Running transaction check
---> Package kernel.i686 0:2.6.23.15-80.fc7 set to be erased
---> Package kernel.i586 0:2.6.21-1.3194.fc7 set to be installed
--> Finished Dependency Resolution

Dependencies Resolved

=============================================================================
Package Arch Version Repository Size
=============================================================================
Installing:
kernel i586 2.6.21-1.3194.fc7 fedora 15 M
Removing:
kernel i686 2.6.23.15-80.fc7 installed 44 M

Transaction Summary
=============================================================================
Install 1 Package(s)
Update 0 Package(s)
Remove 1 Package(s)

Total download size: 15 M
Is this ok [y/N]:

我用UNAME －A是这样的：
[lzh@pacific-lzh ~]$ uname -a
Linux pacific-lzh 2.6.21-1.3194.fc7 #1 SMP Wed May 23 22:35:01 EDT 2007 i686 i686 i386 GNU/Linux

两个疑问：
1、为什么升级会越升越小？提示已经安装了2.6.23啊
2、为什么用UNAME看到的是2.6.21？而yum的时候去不同？