Image forming apparatus having removable external memory and its control method

An image forming apparatus comprising:

• reading means for converting image data, which is read from an original, into electronic data;
• first memory means for storing the electronic data;
• facsimile means for transmitting the electronic data by using a public line or storing image data received from the public line in the first memory means;
• external interface means for connecting with a predetermined external unit to receive image data to be printed, storing data in the first memory means, transmitting data stored in the first memory means to an external unit, or a combination thereof;
• printing means for printing the electronic data stored in the first memory means;
• connecting means from which second memory means can be removed by a user;
• setting means arranged to enable a backup mode or a memory extension mode to be previously set as an operating mode of the secondary memory means connected to the connecting means;
• and
• control means for, when the second memory means is connected, (1) if the backup mode is set by the setting means, storing in and reading from the second memory means at least one of the electronic data, management information for managing image electronic data, and a telephone book used by the facsimile means, which are stored in the first memory means, and (2) if the memory extension mode is set by the setting means, using the second memory means as an extension area of the first memory means and increasing an upper limit of an image memory management information of the management information to thereby expand a memory capacity of the first memory means,
• wherein the control means causes the second memory means to be used as an expansion area of the first memory means and to be used for improving performance of the image forming apparatus by increasing a total number of sheets that can be stored in memory and increasing operation speeds of a scanner and a printer, and
• wherein the control means causes a memory management program to operate in parallel with a program for realizing a function of the image forming apparatus when a recording speed to the second memory means is different from a recording speed to the first memory means, and wherein the program for realizing the function uses only the first memory means and, after a predetermined amount of time passes, the memory management program automatically stores data that is stored in the first memory means in the second memory means.