Seagate Barracuda iMac 1TB Hard Disk Drive 655-1565A 3.5" ST31000528AS Terabyte HDD (1000GB)

Apple Logo manufactured by Seagate for Apple iMac systems. Fits 21.5" 2009/2010/2011 A1311 and A1312 (27") 2009-2011 iMac systems among others. Has 4pin connector at rear of SATA port for temperature sensor. 

Also compatible with 27" A1419 Retina HD, 4K and 5K models (Drive is Fusion capable)
Also perfect upgrade for 2007-2009 A1224/A1225 iMac compatible
Works with most Mac Pro Towers

Apple Part No. 655-1565A
Seagate P/n. ST31000528AS 7200.12 (9SL154-040) 
Size of Memory: 1000Gb (1 Terabyte)
Type: 3.5" Serial-ATA (SATA) 
Drive Speed: 7200rpm 
F/w: AP24
SKU: TBS-655-1565 
Compatibility: iMac A1311/A1312 2009/2010/2011 ** 
** Please be aware that this Seagate 7200.12 Hard Disk (ST31000528AS) although has the same part number as many other Seagate drives this is an Apple approved drive with the Apple Part Number on 655-1565A and has the connection on drive for the Seagate HD sensor, by using non-Apple approved your fans will spin at full speed and the iMac will be too noisy to work comfortably with, plus power management and cooling will be hindered** 
Apple approved drives are designed for Apple and work seamlessly with iMac and Mac Pro systems. 

For an additional £19.99 an OSX of your choice can be pre-installed making drive plug and play when it arrives. Anything from OS X Tiger, Lion and Snow Leopard to the newer High Sierra, Catalina and Mojave operating systems