Magento

hi,
I want to know where are the types of blocks of layout that refer the model class.
for exemple:
<reference name="right">
<block type="catalog/product_new" name="home.catalog.product.new" as ="new" template="catalog/product/new.phtml"/>
</reference>
I want to know where is type="catalog/product_new" that exists in catalog.xml.
If you have more information about the attribute type.i have already read some articles,i found this definition of the attribute type:
type – This is the identifier of the module class that defines the functionality of the block. This attribute must not be modified.
but i didn’t understand how can i get the value of the attribute type.
I wait for your responses.

thank you.