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A comment on I've now played with a Raspberry Pi 400 for a week and here are my conclusions. Parent comment

Re:I've now played with a Raspberry Pi 400 for a week and he... by castratikron on Friday November 20, 2020 @11:48AM (#25162184)
I browsed the datasheet [1] for the BCM2711 processor and did not see an eMMC controller on this part. Assuming the SD card is connected by SPI which would explain why it's so slow. Also rules out eMMC.

[1] https://datasheets.raspberrypi.org/bcm2711/bcm2711-periphera...

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Re:I've now played with a Raspberry Pi 400 for a week and he... by PragmaticPulp on Friday November 20, 2020 @01:53PM (#25163585)
The Raspberry Pi Compute Module 4 has eMMC.

Jeff Geerling benchmarked it and found it faster than his fastest SD card: https://www.jeffgeerling.com/blog/2020/raspberry-pi-compute-...

It's definitely not NVMe fast, but it's perfect for average workloads.

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Re:I've now played with a Raspberry Pi 400 for a week and he... by castratikron on Friday November 20, 2020 @04:00PM (#25164874)
Weird. So the processor has an eMMC controller but they left that out on the datasheet.
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Re:I've now played with a Raspberry Pi 400 for a week and he... by makomk on Friday November 20, 2020 @06:44PM (#25166522)
The publicly-available datasheets for the SoC in the Pi are incredibly, and as far as I can tell intentionally, incomplete. The SD card controller is just one of the things lacking public documentaiton.
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Re:I've now played with a Raspberry Pi 400 for a week and he... by fest on Friday November 20, 2020 @01:32PM (#25163344)
The physical layer for eMMC is SDIO- the same is used for SD cards, at least if you want more than ~ a megabyte/s of interface bandwidth.

IIRC the layers above SDIO are slightly different for eMMC and SD(HC), but generally SoCs that have SDIO interface support both types of memory.

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