| ALOT |
 |
A LOT |
Perhaps this common spelling error began because there does exist in English a word spelled “allot” which is a verb meaning to apportion or grant. The correct form, with “a” and “lot” separated by a space is perhaps not often encountered in print because formal writers usually use other expressions such as “a great deal,” “often,” etc.
You shouldn’t write “alittle” either. It’s “a little.”