This is a remarkable virus, from a technical point of view, as it is the first multipartite virus.
Thanksgiving is able to operate both as a boot sector virus and also as a file virus.
As a boot sector virus it is able to infect the partition table on hard disks, storing the original sector on track 0, head 0, sector 4. When infecting diskettes, it will format an extra track, where it stores the original boot sector, as well as the rest of the virus code. When the virus is executed, it will load itself into memory and monitor the execution of programs. When a non-infected COM file is executed, it will be infected. The virus adds 1253 bytes to all programs it infects.