I have an old 2020 which I can't use now (cable went all-encrypted and the 2020 doesn't get the new IR codes), but most of mine are 5000-series models. Drives can be replaced, although it is getting harder to find parallel ATA drives. Use a USB-IDE adapter and you don't need to open the computer case.
There's 2 ways, an internet site called LaHo (Last Hope ...) or a Windows program called WiRNS (Windows Replay Network Server) which I use. You still need a guide source (usually Schedules Direct, $25/ year).
The alternatives I mentioned include guides.
It can be used with cable, or antenna (although antenna doesn't work as well).
That is one use for it. One of the major advantages of Replay is that the digital recordings are available (most DVRs keep them locked up).
BTW, Replay isn't HD but it DOES handle widescreen.