How often does MS Update

How often does MS put out a new UPDATE program?  Not the actual updates but the program to check for updates.  I did Windows Help & Support today and had to install a new version.  Seems like I just had to install one a couple months ago.

 

Christine

Dimension E520 Desktop
MS Media Center Edition 2005 - Current
Intel Core 2 Duo processor E6300
2GB dual-channel DDR2 SDRAM
Integrated Audio - SigmaTel High Def
Video - NVIDIA GeForce 7300 LE
320GB HD
D: is Philips DVD-Rom DROM6316
E: is NEC DVD+-RW ND-3650A
Monitor is E207WFP

Inspiron 6000
Win XP sp2 - Current
Intel Pentium M 730 (1.6ghz/2MB)
Accelerator 900 Graphics
80GB HD
Intel PRO/wireless 2200

Comcast Cable Modem to Alpha Shield firewall to Netgear Router. Wireless to Inspiron 6000 and wire to Dim E520.