Apple's products these days have more or less become impossible to upgrade. But it wasn't always that way, as this mid-90s Mac PowerBook 540c demonstrates.
Sources:
540c PPC sticker image: https://paizhang.info/wp-content/uploads/2019/01/7793_20.jpg
"PowerPC Portables," Macworld, November 1995.
MacUser, May 1997.
NUpowr upgrade card photo: https://www.sekaimon.com/itemdetail/224473321377
In-box NUpowr upgrade photo: https://www.ebay.com/itm/203165067257
"New & Notable," MacUser, May 1997.
SeeWorld MonsterDrive page, 1997: https://web.archive.org/web/19970327220627/http://www.seeword.com/MonsterDrive.html
FWB Hard Disk Toolkit CD-ROM photo: https://archive.org/details/Hard_Disk_Toolkit_Version_2.54.2_14-01228-601_FWB_Software_1998
Quadra 605 photo: https://commons.wikimedia.org/wiki/File:Macintosh_quadra_605_warm.jpg
PowerPC Upgrade Card photo: https://wiki.preterhuman.net/File:500ppc1.jpg
"More PowerBook 5300 Woes," Macworld, February 1996.
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