# PCI max throughput

Hypothetical here, but I want to understand.

Say I have a hand me down machine, 4 PCI slots, 64-bit 33 MHz PCI.

How much data can that PCI bus handle? System bus is 133 MHz.

I want to use one slot for a SATA II card, and the rest for Gig-E cards, building out as fast a NAS as I can. I think one slot may be AGP2x, so that leaves me 2 for Gig-E and one for SATAT II.

Will I saturate, what is the max bandwidth of the PCI bus?

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you'll certainly saturate the PCI bus before you get anywhere close to full SATA-II speed. (dunno about the gig-E, but suspect it's similar.) i've a similar system and just put in an SATA-II card; my SATA-II drives read at approx. 60-70 MB/sec. much better than IDE drives, so it's worthwhile for my purposes. (not posted as an answer since i don't have time to calculate max theoretical speeds and such.) – quack quixote Nov 8 '09 at 9:49

## 1 Answer

According to Wikipedia's PCI article and List of device bandwidths, PCI bus bandwidths can be calculated with the following formula:

``````frequency * bitwidth = bandwidth
33.33 MHz * 32 bits = 1067 Mbit/s = 133.32 MB/s
``````

Conventional PCI buses operate with the following bandwidths:

• PCI 32-bit, 33 MHz: 1067 Mbit/s or 133.33 MB/s
• PCI 32-bit, 66 MHz: 266 MB/s
• PCI 64-bit, 33 MHz: 266 MB/s
• PCI 64-bit, 66 MHz: 533 MB/s

According to the same links:

• SATA (SATA-150): 150 MB/s
• SATA (SATA-300): 300 MB/s
• Fast Ethernet (100base-X): 11.6 MB/s
• Gig-E (1000base-X): 125 MB/s

Theoretically, it looks like you've got room on the PCI bus for two Gig-E cards, or a SATA-II card, but not both. At least, not running at theoretical maximums. If you put in all three, running them all at full load will bottleneck at the PCI bus.

Fortunately, you won't come close to hitting theoretical speeds on the SATA interface (unless you're using expensive SSD drives). Your Gig-E cards will probably come closer, but in all cases the real-world speeds will be significantly less than theoretical speeds.

I expect such a setup will work fine for many applications.

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