Figured I’d try this here, as I could not locate a Yamaha forum that specializes strictly in digital pianos. 

I’ve owned a CP50 for several months now.  Recently decided to audition some new, piano sounds that were sent to me.
These were supplied on a thumb drive, so I studied the manual, and refence guide.  Unfortunately quite a bit of ‘how to’ information is lacking.
There are no clear instructions as to the process of assigning sound files to the Ext. bank, nor how exactly to save Ext. banks back to a thumb drive.
The instrument seems to default to loading from, and saving to a User bank; rather limiting, it seems. Yet the manual and reference guide indicate that this can also be done with the Ext. banks; it just doesn’t explain how to do so.

Is anyone familiar with the ins-and-outs of CP50 bank / memory usage, or could possibly point me to a tutorial, perhaps ?

Thanks much....

When you SAVE a FILE on a CP5 or CP50, you can opt to save an ALL data file - this will Save the 120 Performances in your USER 1, USER 2, USER 3 banks plus, all the User Songs, and you Utility mode settings, the file will be given the extension .C5A in a CP5 and .C6A in a CP50. This file does not contain the EXT BANK data - which is handled separately.

Additionally, you could opt to save the 120 Performances you’ve created and stored to the EXT Bank. You can write to this bank, only when you have USB stick connected. This Save function is more used to transfer an EXT Bank to a different USB stick. Although it is called an EXTERNAL BANK, it is really internal (inside the CP), it is called External because it depends on the external drive to backup/restore its data between power cycles.

The following should be helpful ........

(EXTBANK.C6E = CP50  and  EXTBANK.C5E (CP5) are the designations for the so-called External Bank (120 Performances). These can be transferred from a USB drive to the volatile EXT memory Bank on-board the instrument. This Bank of 120 PERFORMANCES will disappear when the instrument is powered down. So you can keep one EXTBANK.CxE file in the root directory of your USB stick. When you attach the drive you will be asked if you want to Load the Ext Performances to the (internal) Ext Bank.

– This file is automatically created by the CP5/50 whenever you insert a USB stick for the first time. It is written to the root directory of the drive. In addition to the 3 USER BANKS (120) on board Performances, you can have 3 EXTERNAL BANKS (120) that are transferred in via the USB drive. 

Examples of how it is useful:
If you were going on tour and specified a CP50, before leaving home you could transfer all the USER PERFORMANCES you use to an EXT BANK - take that USB stick on the road. When you arrive, you simply plug your drive into the instrument, it will ask you if you want load your Ext bank of the CP50. When you do, you can put the drive back in your pocket, and play your Performances from the rented unit. At the end of the night when you power down, your sounds disappear - no one can grab your setups. And you did not have to disturb the User Banks of the borrowed instrument. 

Example #2:
The Church owns a CP5 or CP50, and there are several musicians who use the instrument, each could have their own USB stick that included there own setups… Just walk up, plug in, and answer Yes to the Load prompt. Each player immediately has access to their programs without disturbing the instruments USER banks or each other.

Each USB stick can contain 1 EXT BANK file.

Using it:
You can write individual PERFORMANCE data to the [EXT] bank only while a USB stick is inserted. Here is why it exists: The kind of memory that is the USER bank (that remains between power cycle) is very expensive. The EXT bank kind of memory (volatile) is a lot less expensive. Taking advantage of the USB storage device, the EXT bank gives you an additional 3 Banks of 40 locations each. It is like a ‘virtual’ bank. When the drive is in the slot you can write to it and be assured that your latest edits will return when you power up next time with your USB stick.

The EXT BANK is actually on board the instrument in volatile memory - this is why you must load it from the FILE each time.

This is a file type that the CP5/50 makes by itself. Remember the CP5/50 will create an EXT bank automatically as soon as you insert a new USB stick, if the drive does not already have one. It has just “placeholder” init data in it. But you can write to it immediately, by overwriting the initialize data in each location.

How the EXT bank works: 
You computer savvy people know how this works – the [EXT] bank is a RAM bank, a volatile RAM bank – meaning it loses its memory at power down. You can write to the [EXT] bank as long as you have a USB stick in the slot. If you remove the USB stick yes, the sounds are still in the EXT bank and are playable. But the Voices are in RAM (they are backed up on the drive). If you remove the drive the Voices are in limbo now. (Limbo means they are in danger – not permanently backed up). If you power down - the EXT bank is emptied.

When you insert a USB stick that contains a EXTBANK file on it, you will be asked if you wish to load it into RAM. 

Analogy: You are working on a word processor and you put a disk in the drive… you load your document in – it loads into RAM, volatile RAM. Your document will still be there and readable if you remove the source  drive, right? – of course. But your document is not backed up since you last removed the disk. The document is in limbo. If you were to power down now the document would disappear – RAM would be emptied. The backup is on the disk, which you can load next time you power up.

Hope that helps.

Thanks much, Bad_Mister !  I appreciate the tutorial; spot-on instructions, as usual. 
Lots of hidden power in the CP50; looking forward to exploring that....