An index card based notetaking system can be realized with many tools. It is possible to use physical flashcards or take advantage of a digital only workflow. Both systems have pros and cons and the shared similarity is that content is put always into frames.
A frame is a box which holds around 500 byte which is equal to 500 characters or 100 words (around). This definition allows to separate between note taking systems which have no upper limit and which one who has the 500 byte limit. The interesting question why it is important to restrict the amount of a text in a sheet?
Let us take a look into more classical and widespread methods of notetaking. What most students are using are empty books to write down notes. Other are prefering folders to insert new sheets at any position. If the idea is to use a laptop to make notes, that the average user will open a text editor and create a file. From a technical perspective there is no limitation in the file size. On a computer a text file can become 1 megabyte in size and on a physical paper it is possible to use office folders which can fold 500 sheet of papers. This provides for the user an unlimited amount of space.
The most obvious difference is, that physical index cards and hypercard like note taking systems have a strict size limitation. In the famous cardfile.exe program which was introduced for Windows 3.1 the size limit was 479 byte including the title. The user was not allowed to create longer cards which includes scrolling. This limitiation together with the limitation of physical index cards is the underlying secret of efficient note taking.
From a technical perspective a longer amount of information is split into smaller chunks which has 500 byte each. For practical reasons, most index cards are filled only with 400 byte or less which will increase the number of cards. And the unsolved question is, why exactly is there a need to create lots of smaller cards, instead of one huge one?
The reason is that smaller cards are producing automatically a network of thought. If the content is distributed over different locations there is need to connect the nodes in a graph. Otherwise important information gets lost. In contrast a text which is stored in a single file is not connected to anything. It is a linear text from top to bottom without internal cross references.
A limit of 500 byte for a single frame produces automatically some sort of hypertext. And the absence of a space limitation will avoid hypertext.
Let us make a small experiment for reason of better understanding. Suppose the idea is to use a very tiny sheet of paper. On each note only a single word can be written down but not more. An example sentence would look the following way:
[The] [quick] [brown] [fox] [jumps] [over] [the] [lazy] [dog.]
There are 9 sheet of paper and after writing it down the sorting order will become chaotic. If the cards are mixed the original sorting order gets lost. To reproduce the original sentence there is need to numbering the sheets.
If the same sentence is written down on a single sheet of paper there is no need for connecting the nodes together because they have a fixed sorting order.