3 ms·

Was there really a time where HDDs were to slow for 40MB/s but we still had 400MB of RAM? Did I miss a factor of 2 because of the I/Q?

myself248 7y ago
Depends on the box, but some years ago, I picked up an old slotted-Xeon server at a swap for a few bucks, and it had 32 DIMM slots on an enormous memory sub-board. Took registered or buffered ECC, as I recall. I scored a few modules on eBay and put 256MB into it, I think it would've gone to 4GB if I filled all the slots. But the hard drives were SCSI SCA-2, which I believe maxed out at 40MB/s but in practice the drives were much slower. So yes, there was probably a point in time where a reasonably-beefy box would have had the specs you describe.
ahakki 7y ago
I mean SATA 3 has a bit more than 500MB/s right, and PCIe SSDs run at between 1-4 GB/s? so a machine today (at least 8GB of RAM maybe in the hundreds) would have an even bigger ratio between memory size and disk transfer speed.
aidenn0 7y ago
I had a P3 desktop with a UDMA hard drive (33MB/s theoretical peak) and 128MB of RAM. A workstation of the time would have over 512MB of RAM and a SCSI drive that might not sustain 40MB/s. Going back further, in 1995, a SPARCstation 20 had a SCSI-2 controller (10MB/s maximum transfer rate) and could be fitted with 512MB of RAM.
deleted 7y ago
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rachelbythebay 7y ago
20 MHz --> 40M samples per second (Nyquist). 16 bits per channel, and two channels (I, Q). 40000000 x 2 x 2, so... about 160 MB/sec? It's a lot of data. It wasn't happening with the disk I had on hand, so I went for the ramdisk thing. 1.6 GB of memory? That I did have.
- jcims 7y ago
  Would be nice if you could use flowgraphs to program any fpgas on the radio.
  - madengr 7y ago
    You can with RFNoc blocks in GNU Radio, but that’s specific to Ettus hardware.
- rrss 7y ago
  I think you have an extra factor of two there. If you need 20 MHz without aliasing, you either need real sampling at 40 MS/s or IQ sampling at 20 MS/s, but IQ sampling at 40 MS/s is overkill. Nyquist works differently if your samples are complex.
- madengr 7y ago
  20 MHz only requires 20 Msps of complex samples. It would be 40 Msps if those were real samples.

myself248 7y ago

Depends on the box, but some years ago, I picked up an old slotted-Xeon server at a swap for a few bucks, and it had 32 DIMM slots on an enormous memory sub-board. Took registered or buffered ECC, as I recall. I scored a few modules on eBay and put 256MB into it, I think it would've gone to 4GB if I filled all the slots. But the hard drives were SCSI SCA-2, which I believe maxed out at 40MB/s but in practice the drives were much slower. So yes, there was probably a point in time where a reasonably-beefy box would have had the specs you describe.

ahakki 7y ago

I mean SATA 3 has a bit more than 500MB/s right, and PCIe SSDs run at between 1-4 GB/s? so a machine today (at least 8GB of RAM maybe in the hundreds) would have an even bigger ratio between memory size and disk transfer speed.

aidenn0 7y ago

I had a P3 desktop with a UDMA hard drive (33MB/s theoretical peak) and 128MB of RAM. A workstation of the time would have over 512MB of RAM and a SCSI drive that might not sustain 40MB/s. Going back further, in 1995, a SPARCstation 20 had a SCSI-2 controller (10MB/s maximum transfer rate) and could be fitted with 512MB of RAM.

deleted 7y ago

[deleted]

rachelbythebay 7y ago

20 MHz --> 40M samples per second (Nyquist). 16 bits per channel, and two channels (I, Q). 40000000 x 2 x 2, so... about 160 MB/sec? It's a lot of data. It wasn't happening with the disk I had on hand, so I went for the ramdisk thing. 1.6 GB of memory? That I did have.

jcims 7y ago
Would be nice if you could use flowgraphs to program any fpgas on the radio.
- madengr 7y ago
  You can with RFNoc blocks in GNU Radio, but that’s specific to Ettus hardware.
rrss 7y ago
I think you have an extra factor of two there. If you need 20 MHz without aliasing, you either need real sampling at 40 MS/s or IQ sampling at 20 MS/s, but IQ sampling at 40 MS/s is overkill. Nyquist works differently if your samples are complex.
madengr 7y ago
20 MHz only requires 20 Msps of complex samples. It would be 40 Msps if those were real samples.