[0x457]

Because consoles don't use off-the-shelf CPUs for many reasons. Neither Intel nor AMD of that time would even consider making a bespoke CPU for Sony or MS.

Even they could use off-the-shelf SKU it wouldn't be viable - neither one had one that fits in power envelope (not that it helped xbox...)

[pezezin]

Consoles used off-the-shelf CPUs until the 6th generation. Even the Dreamcast and the first Xbox used off-the-shelf CPUs, it was only the PS2 and the GameCube that started the trend of using custom-made CPUs.

[phire]

Not entirely accurate.

The PSX's CPU is semi-custom. The core is a reasonably stock R3000 CPU, but the MMU is slightly modified and they attached a custom GTE coprocessor.... I guess you can debate if attaching a co-processor counts as custom or not (but then the ps4/xbone/ps5/xbs use unmodified AMD jaguar/zen2 cores)

IMO, the N64's CPU counts as off-the-shelf... however the requirements of the N64 (especially cost requirements) might have slightly leaked into the design of the R4300i. But the N64's RSP is a custom CPU, a from scratch MIPS design that doesn't share DNA with anything else.

But the Dreamcast's CPU is actually the result of a joint venture between Hitachi and Sega. There are actually two variants of the SH4, the SH4 and SH4a. The Dreamcast uses the SH4a (despite half the documentation on the internet saying it uses the SH4), which adds a 4-way SIMD unit that's absolutely essential for processing vertices.

We don't know how much influence Sega's needs had over the whole SH4 design, but the SIMD unit is absolutely there for the Dreamcast, I'm pretty sure it's the first 4-way floating point SIMD on the market. The fact that both the SH4/SH4a were then sold to everyone else, doesn't mean they were off the shelf.

Really, the original Xbox using an off-the-shelf CPU is an outlier (technically it's a custom SKU, but really it's just a binned die with half the cache disabled).