What does Bytes In / Out mean?

When viewing performance metrics for a computer, you might see something like "Bytes In" or "Bytes Out".

What does this mean, and how does this related to "Upload" and "Download"?

Is it "Bytes In = Upload and Bytes Out = Download" or the reverse?

Example (Not my server)

3 Answers

The network is always considered to be the "outside", and the CPU etc. to be the "inside".

"Bytes In" is the amount of data received through that interface (i.e to your host from the network).

"Bytes Out" is the amount of data sent through that interface (from your host to the network).

Which of those you consider to be "upload" and which to be "download" depends on your view of your system - i.e. whether it is "up" or "down" from what that interface is connected to. If it's a home PC, you probably equate "In" with "download"; for a fileserver, "In" is usually called "upload".

You may also see "In" as "Rx" (i.e. Received) and "Out" as "Tx" (Transmitted), as in the output of ifconfig:

eth1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.x.x netmask 255.255.255.0 broadcast 192.168.x.255 inet6 fe80::xxxx:xxxx:xxxx prefixlen 64 scopeid 0x20<link> ether xx:xx:xx:xx:xx:xx txqueuelen 1000 (Ethernet) RX packets 1813934 bytes 68509518 (65.3 MiB) RX errors 1032120 dropped 0 overruns 0 frame 81778 TX packets 1473055 bytes 1797493199 (1.6 GiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 699501 device interrupt 18 

or

eth0 Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx inet addr:172.20.x.x Bcast:172.20.x.255 Mask:255.255.255.0 inet6 addr: fe80::xxxx:xxxx:xxxx:xxxx/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:36387424 errors:0 dropped:0 overruns:0 frame:0 TX packets:15636657 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:6378638797 (6.3 GB) TX bytes:14222465675 (14.2 GB) Interrupt:20 Memory:e0380000-e03a0000 

(two different implementations of ifconfig; identifying details x'ed out)

Some tools (e.g. xosview) may show an aggregate of all network interfaces, i.e. total sent and received on all network interfaces. Then, the upstream/downstream terminology is unhelpful if some of the networks are "up" and some are "down".

In general (and without arguing about other possible uses and semantics):

"Upload" means you're sending, so (the majority of related) bits are going OUT.
"Download" means you're receiving, so (the majority of related) bits are coming IN.

Packets need responses (again, in general), so there will be bits of data flowing in the opposite direction to let one end know the other end received the last packet sent.

It simply means how much data you are consuming through that network.

You can calculate it into Megabytes by following calculation:

1 Megabyte = 1048576 Bytes

1 Kilobyte = 1024 Bytes

'In' means download and 'Out' means upload. 'In' would be greater than the 'Out' because there is less upload than download.