Finding bootloader in arduino ide

Hi, I use the arduino nano board. How do I locate the bootloader? I had the wrong bootloader once and could not upload programs. Every so often I see bootloader and old bootloader pop up . I know that I have to select 'old bootloader' to upload programs.
How do I find which bootloader I am using before uploading? And I would really like somehow to find the uno bootloader so that I can program my atmega 328p mcu which has the uno bootloader pre-installed.
Any help would be appreciated. Thanks.

Generally, you select your board type with Tools -> Board: and your programmer type with Tools -> Programmer and then select Tools -> Burn Bootloader to get the right bootloader installed.

The "hardware/avr/1.8.5/boards.txt" file will tell you what bootloader goes with each board definition. You will find the sources and pre-built binaries under: "hardware/avr/1.8.5/bootloaders"

Hi John, When I press' tools>burnbootloader' I get 'error while burning bootloader'. My board is arduino nano. The programmer is AVRISP mk11.
Can't find those files you refer to. Are they supposed to be on my computer somewhere? Copied exactly your quotes and pasted in search. I just get a web reference. Then it looks really complicated.
I didn't have the board connected when I pressed ' Burn Bootloader'. This looks like you are changing the bootloader. I understood the bootloader was already installed. As I said I sometimes see 'bootloader' and 'old bootloader' pop up on the screen. If I don't press old bootloader I can't upload to my nano board.
Can you tell me how I can see 'bootloader' and 'old bootloader' on my screen because I know if I have the wrong bootloader I cannot upload a program to my nano board.

Hi John, Found part of what I wanted. Under processor there are 2 listings for atmega 328p. One listing shows 'bootloader' and 'old bootloader'. The other just shows atmega 328p. I always have to select 'old bootloader' to be able to upload to my nano board. I can presume that the bootloader software is on the board, not on my computer.
I now have a atmega 328p mcu which claims to have a uno bootloader installed. I also now have a usb to serial/ttl adapter connected to this mcu. The idea here being that you don't need the arduino nano board to upload to the mcu. You just need a program.
I tried to upload the arduino 'blink' example. No luck. got different error messages at different times. 'can't find file specified', 'programmer not responding', 'not in sync'. It seems to try to upload for a long time until finally you get one of those error messages.
I am sure it is a bootloader problem as I get the same error messages when I don't use 'old bootloader'.
Any suggestions to fix John?
The article I was following was from 'electronics lab' which was called 'programming atmega 328p mcu with arduino ide. It showed all the connections required between the adaptor and mcu which I followed to the letter.

If "all the connections" did not include a small capacitor connecting the USB-Serial adapter to the Reset pin of the Nano then you need to manually reset the Nano when you try to upload.

I think you mean reset pin of the atmega 328p mcu(with uno bootloader installed). The whole purpose of using the adaptor is to do away with the nano board for programming.
The article referred to says that the nano board is an overkill for programming the 328. If you have a program on your laptop you just have to upload it via the adaptor.
Yes there is a capacitor connecting the usb-serial adaptor to the reset pin in the connections. I have it installed.
The problem has to be the uno bootloader John. Under processor all I have is atmega 328p bootloader and old bootloader. It seems to me there should be another entry 'uno bootloader' here because it has been pre-installed on the atmega 328p mcu(with uno bootloader installed).
If I could get some kind of download to my processor entry in tools in the arduino ide of an entry 'uno bootloader' I may be able to download a program. The bootloaders there now are nano bootloaders.

John, Just noticed when you select uno board the processor entry disappears from tools. This is usually where the bootloaders are listed.

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