Currently I have a Magento shopping cart running on iweb share web hosting.
Recently, customers complain that the page is sometime blank, and I found that it is because 500 error with not enough memory.
I told the admin guy, he provided me a script which use php memory_get_peak_usage
He said the application require 32mb to run, and said if 30 concurrent people visit the page, that mean 32mb X 30 which is almost 1000mb for memory cost.
I am not sure if he tells the truth or not, because for Magento, even turn on the cache of Magento, it requires 3mb.
So I am wondering if memory_get_peak_usage X concurrent users is equal to the total memory usage?
Your admin guy is over simplifying things a bit, but what he's saying essentially rings true. Magento is a RAM hog. The leading Magento hosts (affiliate link, click it and buy something and I get a kickback) give their entry level Magento plans 16GB of memory. That's 16,384 GB.
The "iweb share web hosting" is not a suitable server host for Magento. Move your store.