I will like to know about this payment method and how it is processed
by vendors.I will also like to know the similarities and differences
it has with electronic checks.Furthermore I will like to have a list
of computer part vendors that offer this mode of payment.Thank you.

Here are links to 2 good reads on the difference and impact of ACH vs e-checks:

http://ica.hevra.haifa.ac.il/teamco/kim/files/public/5.pdf
http://merchantselect.com/articles/?1000-18.html

As far as vendors go for ACH processing:

http://www.verisign.com/support/payflow/manager/selfHelp/transACH.html
http://www.achbill.com
....and you can find more if you google properly. :)

Computer part vendors usually do not offer ACH. ACH is commonly used
by financial institutions and bill pay providers. A lot of times
e-check payments are processed via ACH by the companies to save
themselves the cost. They do not disclose this to you when they do it.
What commonly happens is that large vendors will contract with smaller
third party companies that handle bill processing. Those companies
will behind the covers employ the fastest and cheapest method of
obtaining your money... which is commonly ACH.

And as always:

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