In addition to other answers
If you upload your file to a fast server, so the link to your ISP is the slowest link in a chain, then the transfer will be limited to 4 Mbps by your ISP – it's true in general for large files.
But if the hardware can do better (i.e. the 4Mbps is an arbitrary limit set by your ISP because you pay for this option only, not some faster one) and your file is small enough then you may experience "burst upload speed".
It means your ISP may allow you to send the first 10 MB (an example, the actual value is set by your ISP) of a file a lot faster than the declared 4 Mbps if your link has been idle (or almost idle) for a while. After these 10 MB the link gets "saturated" and the 4 Mbps limit applies for remaining data. Make your link almost idle for another while and you will be able to burst again.
In other words: if you keep your upload low for a few seconds you gain a credit of some bytes you can upload a lot faster before your limit kicks in.
This mechanism makes your web browsing more snappy, improves uploads of files.
From ISP's point of view many of their clients generate such upward burst only. They (as a group) hardly ever saturate the ISP's link to the Internet (its upload bandwidth) because the bursts occur randomly at different moments, so there's no point in limiting every single connection. Thanks to the bursts these clients are happy with more responsive Facebook when they post their food photos. On the other hand few clients using P2P or sending large files at the same moment may saturate the link to the outside, so they are limited when they exceed some threshold.
A file of 4 Mb in your example is rather small, it is 0.5 MB. It may be transferred a whole within a single burst if your ISP supports it. You may hit some other limit (or temporary network slowdown) somewhere beyond your ISP though.
11File sizes are in MegaBytes (MB), but line speed is in MegaBits (Mb/s). 1MB takes 8 seconds to transfer at 1Mb/s (because there are 8 bits in a standard byte). Your ISP can only advertise the speed they provide, so once your traffic leaves their network, and crosses other networks, there is no guarantee that the speed will remain the same. so no, it is not without regard for location. In practical terms, it will always take additional time to reach half way around the planet than it takes to walk next door. – Frank Thomas – 2016-09-07T12:54:10.350
@FrankThomas Say i want to upload some file on amazon site. Assume myservice provider is PEAK. Do you mean first data will travel to PEAK(and that speed will will be 4 Mbps . So even if it is 4 Mbps between me and my isp then does it mean my data will reach to my ISP irrespective of its location ? I believe NO). Once data reaches to my ISP, it will try to connect Amazon server. Which network ISP is going to connect Amazon server ? I sit common network or PEAK owns network ? – user3198603 – 2016-09-07T17:29:23.113
@user3198603 - You will connect directly to Amazon. Frank's point is, you can only upload at the speeds your ISP provides, but the slowest common denominator could be the desination. It isn't Amazon in this case, who likely will exceed your ISP's capabilties, by several factors. – Ramhound – 2016-09-07T20:37:42.377
1"4 Mb file" Do you really mean a 4 megabit file? Or a 4 megabyte file? – Peter Mortensen – 2016-09-07T22:08:07.943
Note that some connection types will give you different upload and download speeds. – user253751 – 2016-09-07T22:43:06.870
@FrankThomas Why do file sizes need to be in megabytes, you can just as easily express file sizes in Mb as MB. The same with line speeds can just as easily be expressed in MB/s as Mb/s. – Vality – 2016-09-07T22:52:31.663
@Vality Except no one express file sizes in Mb. Not even in the imperial unit system :-) – Pierre Arlaud – 2016-09-08T08:28:34.727
1Note that when you upload a file, it doesn't only transfer the file, but also other meta information, such as HTTP headers, TCP packet wrappers, etc. Depending on the protocol, the actual data you transfer can actually magnify to a notable extent. – SOFe – 2016-09-08T08:54:30.843