Hi marcus,

Yes you can put your iMac 10,1 model into Target Display mode and use it as a 
second monitor.
You will need a bit of a cable mix to get from Thunderbolt 3 to mini display 
port but it can be done.

To get into Target Display mode you need to do this.

Use Target Display Mode
Follow these steps to start using your iMac as a display:

Make sure that your iMac is turned on, and the other Mac is logged in to a 
macOS user account.
Connect the Mini DisplayPort or Thunderbolt cable between the two computers.
Press Command-F2 on the keyboard of the iMac that you want to use as a display.
After you press Command-F2, your iMac displays the desktop from the connected 
Mac.

Have a read of this
https://applerepairstation.co.uk/Technical%20Desk/use-your-imac-as-a-display-with-target-display-mode/
 
<https://applerepairstation.co.uk/Technical%20Desk/use-your-imac-as-a-display-with-target-display-mode/>

regards,

robin




> On 16 Oct 2020, at 3:53 pm, Marcus Harris <cryptodo...@me.com> wrote:
> 
> Hello WAMUGERS,
> 
> I have an Apple 27 inch iMac  iMac10,1  Intel Core 2 Duo Speed:3.06 GHz
> 1 Processor: 2Cores: L2 Cache:3 MB Memory: 8 GB Graphics-ATI Radeon HD 4670, 
> 256 MB Storage 2TB HD 
> System Software  macOS Sierra 10.13.6
> 
> It’s getting pretty slow now as it’s 11 years old and I think it may soon 
> fail. macOS Sierra is the limit for it’s system capability.
> 
> But the screen is fine for my daily work.
> 
> I am considering buying an advertised MacBook Pro (2020) with a quad-core 
> Intel processor and Magic Keyboard. 
> 8th-generation quad-core Intel core i5 processor with Turbo Boost up to 3.9GHz
> 8 GB Ram 256GB SSD
> 
> Will I be able to plug it into my iMac 27 thereby using her as my desktop 
> screen? 
> 
> If not then what is the next best option suggestion to allow me to plug into 
> her screen?
> Perhaps this is a crazy idea!
> 
> BY THE WAY, I use my Mac for writing essays, for spreadsheets, organising my 
> photos , reference browsing and emailing. Nothing high end anymore as I’m now 
> 77.
> 
> I recently bought an iBookPro 12 with pencil for streaming, taking photos, 
> reading and sketching. It’s a great Apple product.
> 
> Regards
> 
> Marcus Harris
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