I only recently realized that my oldest computer system, the first I ever bought, has all been renewed, bar the processor, an old-style P4 (Northwood) purchased July 2004.
The original 80GB HDD, which I loved due to high reliability despite serious punishment (I did so much experimenting with it including multiple OS installations) until it failed earlier this year.
The motherboard failed several months ago (difficult problems involving USB connectivity and lack of sound, all intermittent, all resulting in emotional pain).
The SONY DVD-Writer which I loved due running reliably for years until it failed earlier this year. I also lost the power supply which kept resetting when, say for example I was inserting an optical disk and the HDD was doing much seeking (both of which must have induced unbearable power spikes the PSU), an obvious sign of deterioration, and great source of emotional pain too.
The replacement included a case as well, so yes, even the case ain't original.
Additionally, I was initially all PATA (with those fucking annoying IDE cables) and am all SATA now (luckily the replacement motherboard got 2 SATA ports, which is all I needed since I only got 1 optical drive and 1 HDD).